BPF-HELPERS(7) Miscellaneous Information Manual BPF-HELPERS(7)
NAME
BPF-HELPERS - list of eBPF helper functions
DESCRIPTION
The extended Berkeley Packet Filter (eBPF) subsystem consists in pro-
grams written in a pseudo-assembly language, then attached to one of
the several kernel hooks and run in reaction of specific events. This
framework differs from the older, "classic" BPF (or "cBPF") in several
aspects, one of them being the ability to call special functions (or
"helpers") from within a program. These functions are restricted to a
white-list of helpers defined in the kernel.
These helpers are used by eBPF programs to interact with the system, or
with the context in which they work. For instance, they can be used to
print debugging messages, to get the time since the system was booted,
to interact with eBPF maps, or to manipulate network packets. Since
there are several eBPF program types, and that they do not run in the
same context, each program type can only call a subset of those
helpers.
Due to eBPF conventions, a helper can not have more than five argu-
ments.
Internally, eBPF programs call directly into the compiled helper func-
tions without requiring any foreign-function interface. As a result,
calling helpers introduces no overhead, thus offering excellent perfor-
mance.
This document is an attempt to list and document the helpers available
to eBPF developers. They are sorted by chronological order (the oldest
helpers in the kernel at the top).
HELPERS
void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)
Description
Perform a lookup in map for an entry associated to key.
Return Map value associated to key, or NULL if no entry was
found.
long bpf_map_update_elem(struct bpf_map *map, const void *key, const
void *value, u64 flags)
Description
Add or update the value of the entry associated to key in
map with value. flags is one of:
BPF_NOEXIST
The entry for key must not exist in the map.
BPF_EXIST
The entry for key must already exist in the map.
BPF_ANY
No condition on the existence of the entry for
key.
Flag value BPF_NOEXIST cannot be used for maps of types
BPF_MAP_TYPE_ARRAY or BPF_MAP_TYPE_PERCPU_ARRAY (all el-
ements always exist), the helper would return an error.
Return 0 on success, or a negative error in case of failure.
long bpf_map_delete_elem(struct bpf_map *map, const void *key)
Description
Delete entry with key from map.
Return 0 on success, or a negative error in case of failure.
long bpf_probe_read(void *dst, u32 size, const void *unsafe_ptr)
Description
For tracing programs, safely attempt to read size bytes
from kernel space address unsafe_ptr and store the data
in dst.
Generally, use bpf_probe_read_user() or
bpf_probe_read_kernel() instead.
Return 0 on success, or a negative error in case of failure.
u64 bpf_ktime_get_ns(void)
Description
Return the time elapsed since system boot, in nanosec-
onds. Does not include time the system was suspended.
See: clock_gettime(CLOCK_MONOTONIC)
Return Current ktime.
long bpf_trace_printk(const char *fmt, u32 fmt_size, ...)
Description
This helper is a "printk()-like" facility for debugging.
It prints a message defined by format fmt (of size
fmt_size) to file /sys/kernel/tracing/trace from TraceFS,
if available. It can take up to three additional u64 ar-
guments (as an eBPF helpers, the total number of argu-
ments is limited to five).
Each time the helper is called, it appends a line to the
trace. Lines are discarded while /sys/kernel/trac-
ing/trace is open, use /sys/kernel/tracing/trace_pipe to
avoid this. The format of the trace is customizable, and
the exact output one will get depends on the options set
in /sys/kernel/tracing/trace_options (see also the README
file under the same directory). However, it usually de-
faults to something like:
telnet-470 [001] .N.. 419421.045894: 0x00000001: <formatted msg>
In the above:
• telnet is the name of the current task.
• 470 is the PID of the current task.
• 001 is the CPU number on which the task is running.
• In .N.., each character refers to a set of options
(whether irqs are enabled, scheduling options,
whether hard/softirqs are running, level of pre-
empt_disabled respectively). N means that
TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED are set.
• 419421.045894 is a timestamp.
• 0x00000001 is a fake value used by BPF for the in-
struction pointer register.
• <formatted msg> is the message formatted with fmt.
The conversion specifiers supported by fmt are similar,
but more limited than for printk(). They are %d, %i, %u,
%x, %ld, %li, %lu, %lx, %lld, %lli, %llu, %llx, %p, %s.
No modifier (size of field, padding with zeroes, etc.) is
available, and the helper will return -EINVAL (but print
nothing) if it encounters an unknown specifier.
Also, note that bpf_trace_printk() is slow, and should
only be used for debugging purposes. For this reason, a
notice block (spanning several lines) is printed to ker-
nel logs and states that the helper should not be used
"for production use" the first time this helper is used
(or more precisely, when trace_printk() buffers are allo-
cated). For passing values to user space, perf events
should be preferred.
Return The number of bytes written to the buffer, or a negative
error in case of failure.
u32 bpf_get_prandom_u32(void)
Description
Get a pseudo-random number.
From a security point of view, this helper uses its own
pseudo-random internal state, and cannot be used to infer
the seed of other random functions in the kernel. How-
ever, it is essential to note that the generator used by
the helper is not cryptographically secure.
Return A random 32-bit unsigned value.
u32 bpf_get_smp_processor_id(void)
Description
Get the SMP (symmetric multiprocessing) processor id.
Note that all programs run with migration disabled, which
means that the SMP processor id is stable during all the
execution of the program.
Return The SMP id of the processor running the program.
long bpf_skb_store_bytes(struct sk_buff *skb, u32 offset, const void
*from, u32 len, u64 flags)
Description
Store len bytes from address from into the packet associ-
ated to skb, at offset. flags are a combination of
BPF_F_RECOMPUTE_CSUM (automatically recompute the check-
sum for the packet after storing the bytes) and BPF_F_IN-
VALIDATE_HASH (set skb->hash, skb->swhash and skb->l4hash
to 0).
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_l3_csum_replace(struct sk_buff *skb, u32 offset, u64 from, u64
to, u64 size)
Description
Recompute the layer 3 (e.g. IP) checksum for the packet
associated to skb. Computation is incremental, so the
helper must know the former value of the header field
that was modified (from), the new value of this field
(to), and the number of bytes (2 or 4) for this field,
stored in size. Alternatively, it is possible to store
the difference between the previous and the new values of
the header field in to, by setting from and size to 0.
For both methods, offset indicates the location of the IP
checksum within the packet.
This helper works in combination with bpf_csum_diff(),
which does not update the checksum in-place, but offers
more flexibility and can handle sizes larger than 2 or 4
for the checksum to update.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_l4_csum_replace(struct sk_buff *skb, u32 offset, u64 from, u64
to, u64 flags)
Description
Recompute the layer 4 (e.g. TCP, UDP or ICMP) checksum
for the packet associated to skb. Computation is incre-
mental, so the helper must know the former value of the
header field that was modified (from), the new value of
this field (to), and the number of bytes (2 or 4) for
this field, stored on the lowest four bits of flags. Al-
ternatively, it is possible to store the difference be-
tween the previous and the new values of the header field
in to, by setting from and the four lowest bits of flags
to 0. For both methods, offset indicates the location of
the IP checksum within the packet. In addition to the
size of the field, flags can be added (bitwise OR) actual
flags. With BPF_F_MARK_MANGLED_0, a null checksum is left
untouched (unless BPF_F_MARK_ENFORCE is added as well),
and for updates resulting in a null checksum the value is
set to CSUM_MANGLED_0 instead. Flag BPF_F_PSEUDO_HDR in-
dicates the checksum is to be computed against a
pseudo-header.
This helper works in combination with bpf_csum_diff(),
which does not update the checksum in-place, but offers
more flexibility and can handle sizes larger than 2 or 4
for the checksum to update.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_tail_call(void *ctx, struct bpf_map *prog_array_map, u32 in-
dex)
Description
This special helper is used to trigger a "tail call", or
in other words, to jump into another eBPF program. The
same stack frame is used (but values on stack and in reg-
isters for the caller are not accessible to the callee).
This mechanism allows for program chaining, either for
raising the maximum number of available eBPF instruc-
tions, or to execute given programs in conditional
blocks. For security reasons, there is an upper limit to
the number of successive tail calls that can be per-
formed.
Upon call of this helper, the program attempts to jump
into a program referenced at index index in prog_ar-
ray_map, a special map of type BPF_MAP_TYPE_PROG_ARRAY,
and passes ctx, a pointer to the context.
If the call succeeds, the kernel immediately runs the
first instruction of the new program. This is not a func-
tion call, and it never returns to the previous program.
If the call fails, then the helper has no effect, and the
caller continues to run its subsequent instructions. A
call can fail if the destination program for the jump
does not exist (i.e. index is superior to the number of
entries in prog_array_map), or if the maximum number of
tail calls has been reached for this chain of programs.
This limit is defined in the kernel by the macro
MAX_TAIL_CALL_CNT (not accessible to user space), which
is currently set to 33.
Return 0 on success, or a negative error in case of failure.
long bpf_clone_redirect(struct sk_buff *skb, u32 ifindex, u64 flags)
Description
Clone and redirect the packet associated to skb to an-
other net device of index ifindex. Both ingress and
egress interfaces can be used for redirection. The
BPF_F_INGRESS value in flags is used to make the distinc-
tion (ingress path is selected if the flag is present,
egress path otherwise). This is the only flag supported
for now.
In comparison with bpf_redirect() helper, bpf_clone_redi-
rect() has the associated cost of duplicating the packet
buffer, but this can be executed out of the eBPF program.
Conversely, bpf_redirect() is more efficient, but it is
handled through an action code where the redirection hap-
pens only after the eBPF program has returned.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
Positive error indicates a potential drop or congestion
in the target device. The particular positive error codes
are not defined.
u64 bpf_get_current_pid_tgid(void)
Description
Get the current pid and tgid.
Return A 64-bit integer containing the current tgid and pid, and
created as such: current_task->tgid << 32 | cur-
rent_task->pid.
u64 bpf_get_current_uid_gid(void)
Description
Get the current uid and gid.
Return A 64-bit integer containing the current GID and UID, and
created as such: current_gid << 32 | current_uid.
long bpf_get_current_comm(void *buf, u32 size_of_buf)
Description
Copy the comm attribute of the current task into buf of
size_of_buf. The comm attribute contains the name of the
executable (excluding the path) for the current task. The
size_of_buf must be strictly positive. On success, the
helper makes sure that the buf is NUL-terminated. On
failure, it is filled with zeroes.
Return 0 on success, or a negative error in case of failure.
u32 bpf_get_cgroup_classid(struct sk_buff *skb)
Description
Retrieve the classid for the current task, i.e. for the
net_cls cgroup to which skb belongs.
This helper can be used on TC egress path, but not on
ingress.
The net_cls cgroup provides an interface to tag network
packets based on a user-provided identifier for all traf-
fic coming from the tasks belonging to the related
cgroup. See also the related kernel documentation, avail-
able from the Linux sources in file Documentation/ad-
min-guide/cgroup-v1/net_cls.rst.
The Linux kernel has two versions for cgroups: there are
cgroups v1 and cgroups v2. Both are available to users,
who can use a mixture of them, but note that the net_cls
cgroup is for cgroup v1 only. This makes it incompatible
with BPF programs run on cgroups, which is a
cgroup-v2-only feature (a socket can only hold data for
one version of cgroups at a time).
This helper is only available is the kernel was compiled
with the CONFIG_CGROUP_NET_CLASSID configuration option
set to "y" or to "m".
Return The classid, or 0 for the default unconfigured classid.
long bpf_skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16
vlan_tci)
Description
Push a vlan_tci (VLAN tag control information) of proto-
col vlan_proto to the packet associated to skb, then up-
date the checksum. Note that if vlan_proto is different
from ETH_P_8021Q and ETH_P_8021AD, it is considered to be
ETH_P_8021Q.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_vlan_pop(struct sk_buff *skb)
Description
Pop a VLAN header from the packet associated to skb.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_get_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key
*key, u32 size, u64 flags)
Description
Get tunnel metadata. This helper takes a pointer key to
an empty struct bpf_tunnel_key of size, that will be
filled with tunnel metadata for the packet associated to
skb. The flags can be set to BPF_F_TUNINFO_IPV6, which
indicates that the tunnel is based on IPv6 protocol in-
stead of IPv4.
The struct bpf_tunnel_key is an object that generalizes
the principal parameters used by various tunneling proto-
cols into a single struct. This way, it can be used to
easily make a decision based on the contents of the en-
capsulation header, "summarized" in this struct. In par-
ticular, it holds the IP address of the remote end (IPv4
or IPv6, depending on the case) in key->remote_ipv4 or
key->remote_ipv6. Also, this struct exposes the key->tun-
nel_id, which is generally mapped to a VNI (Virtual Net-
work Identifier), making it programmable together with
the bpf_skb_set_tunnel_key() helper.
Let's imagine that the following code is part of a pro-
gram attached to the TC ingress interface, on one end of
a GRE tunnel, and is supposed to filter out all messages
coming from remote ends with IPv4 address other than
10.0.0.1:
int ret;
struct bpf_tunnel_key key = {};
ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0);
if (ret < 0)
return TC_ACT_SHOT; // drop packet
if (key.remote_ipv4 != 0x0a000001)
return TC_ACT_SHOT; // drop packet
return TC_ACT_OK; // accept packet
This interface can also be used with all encapsulation
devices that can operate in "collect metadata" mode: in-
stead of having one network device per specific configu-
ration, the "collect metadata" mode only requires a sin-
gle device where the configuration can be extracted from
this helper.
This can be used together with various tunnels such as
VXLan, Geneve, GRE or IP in IP (IPIP).
Return 0 on success, or a negative error in case of failure.
long bpf_skb_set_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key
*key, u32 size, u64 flags)
Description
Populate tunnel metadata for packet associated to skb.
The tunnel metadata is set to the contents of key, of
size. The flags can be set to a combination of the fol-
lowing values:
BPF_F_TUNINFO_IPV6
Indicate that the tunnel is based on IPv6 protocol
instead of IPv4.
BPF_F_ZERO_CSUM_TX
For IPv4 packets, add a flag to tunnel metadata
indicating that checksum computation should be
skipped and checksum set to zeroes.
BPF_F_DONT_FRAGMENT
Add a flag to tunnel metadata indicating that the
packet should not be fragmented.
BPF_F_SEQ_NUMBER
Add a flag to tunnel metadata indicating that a
sequence number should be added to tunnel header
before sending the packet. This flag was added for
GRE encapsulation, but might be used with other
protocols as well in the future.
BPF_F_NO_TUNNEL_KEY
Add a flag to tunnel metadata indicating that no
tunnel key should be set in the resulting tunnel
header.
Here is a typical usage on the transmit path:
struct bpf_tunnel_key key;
populate key ...
bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0);
bpf_clone_redirect(skb, vxlan_dev_ifindex, 0);
See also the description of the bpf_skb_get_tunnel_key()
helper for additional information.
Return 0 on success, or a negative error in case of failure.
u64 bpf_perf_event_read(struct bpf_map *map, u64 flags)
Description
Read the value of a perf event counter. This helper re-
lies on a map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY. The
nature of the perf event counter is selected when map is
updated with perf event file descriptors. The map is an
array whose size is the number of available CPUs, and
each cell contains a value relative to one CPU. The value
to retrieve is indicated by flags, that contains the in-
dex of the CPU to look up, masked with BPF_F_INDEX_MASK.
Alternatively, flags can be set to BPF_F_CURRENT_CPU to
indicate that the value for the current CPU should be re-
trieved.
Note that before Linux 4.13, only hardware perf event can
be retrieved.
Also, be aware that the newer helper
bpf_perf_event_read_value() is recommended over
bpf_perf_event_read() in general. The latter has some ABI
quirks where error and counter value are used as a return
code (which is wrong to do since ranges may overlap).
This issue is fixed with bpf_perf_event_read_value(),
which at the same time provides more features over the
bpf_perf_event_read() interface. Please refer to the de-
scription of bpf_perf_event_read_value() for details.
Return The value of the perf event counter read from the map, or
a negative error code in case of failure.
long bpf_redirect(u32 ifindex, u64 flags)
Description
Redirect the packet to another net device of index
ifindex. This helper is somewhat similar to
bpf_clone_redirect(), except that the packet is not
cloned, which provides increased performance.
Except for XDP, both ingress and egress interfaces can be
used for redirection. The BPF_F_INGRESS value in flags is
used to make the distinction (ingress path is selected if
the flag is present, egress path otherwise). Currently,
XDP only supports redirection to the egress interface,
and accepts no flag at all.
The same effect can also be attained with the more
generic bpf_redirect_map(), which uses a BPF map to store
the redirect target instead of providing it directly to
the helper.
Return For XDP, the helper returns XDP_REDIRECT on success or
XDP_ABORTED on error. For other program types, the values
are TC_ACT_REDIRECT on success or TC_ACT_SHOT on error.
u32 bpf_get_route_realm(struct sk_buff *skb)
Description
Retrieve the realm or the route, that is to say the
tclassid field of the destination for the skb. The iden-
tifier retrieved is a user-provided tag, similar to the
one used with the net_cls cgroup (see description for
bpf_get_cgroup_classid() helper), but here this tag is
held by a route (a destination entry), not by a task.
Retrieving this identifier works with the clsact TC
egress hook (see also tc-bpf(8)), or alternatively on
conventional classful egress qdiscs, but not on TC
ingress path. In case of clsact TC egress hook, this has
the advantage that, internally, the destination entry has
not been dropped yet in the transmit path. Therefore, the
destination entry does not need to be artificially held
via netif_keep_dst() for a classful qdisc until the skb
is freed.
This helper is available only if the kernel was compiled
with CONFIG_IP_ROUTE_CLASSID configuration option.
Return The realm of the route for the packet associated to skb,
or 0 if none was found.
long bpf_perf_event_output(void *ctx, struct bpf_map *map, u64 flags,
void *data, u64 size)
Description
Write raw data blob into a special BPF perf event held by
map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY. This perf
event must have the following attributes: PERF_SAMPLE_RAW
as sample_type, PERF_TYPE_SOFTWARE as type, and
PERF_COUNT_SW_BPF_OUTPUT as config.
The flags are used to indicate the index in map for which
the value must be put, masked with BPF_F_INDEX_MASK. Al-
ternatively, flags can be set to BPF_F_CURRENT_CPU to in-
dicate that the index of the current CPU core should be
used.
The value to write, of size, is passed through eBPF stack
and pointed by data.
The context of the program ctx needs also be passed to
the helper.
On user space, a program willing to read the values needs
to call perf_event_open() on the perf event (either for
one or for all CPUs) and to store the file descriptor
into the map. This must be done before the eBPF program
can send data into it. An example is available in file
samples/bpf/trace_output_user.c in the Linux kernel
source tree (the eBPF program counterpart is in sam-
ples/bpf/trace_output_kern.c).
bpf_perf_event_output() achieves better performance than
bpf_trace_printk() for sharing data with user space, and
is much better suitable for streaming data from eBPF pro-
grams.
Note that this helper is not restricted to tracing use
cases and can be used with programs attached to TC or XDP
as well, where it allows for passing data to user space
listeners. Data can be:
• Only custom structs,
• Only the packet payload, or
• A combination of both.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_load_bytes(const void *skb, u32 offset, void *to, u32 len)
Description
This helper was provided as an easy way to load data from
a packet. It can be used to load len bytes from offset
from the packet associated to skb, into the buffer
pointed by to.
Since Linux 4.7, usage of this helper has mostly been re-
placed by "direct packet access", enabling packet data to
be manipulated with skb->data and skb->data_end pointing
respectively to the first byte of packet data and to the
byte after the last byte of packet data. However, it re-
mains useful if one wishes to read large quantities of
data at once from a packet into the eBPF stack.
Return 0 on success, or a negative error in case of failure.
long bpf_get_stackid(void *ctx, struct bpf_map *map, u64 flags)
Description
Walk a user or a kernel stack and return its id. To
achieve this, the helper needs ctx, which is a pointer to
the context on which the tracing program is executed, and
a pointer to a map of type BPF_MAP_TYPE_STACK_TRACE.
The last argument, flags, holds the number of stack
frames to skip (from 0 to 255), masked with
BPF_F_SKIP_FIELD_MASK. The next bits can be used to set a
combination of the following flags:
BPF_F_USER_STACK
Collect a user space stack instead of a kernel
stack.
BPF_F_FAST_STACK_CMP
Compare stacks by hash only.
BPF_F_REUSE_STACKID
If two different stacks hash into the same
stackid, discard the old one.
The stack id retrieved is a 32 bit long integer handle
which can be further combined with other data (including
other stack ids) and used as a key into maps. This can be
useful for generating a variety of graphs (such as flame
graphs or off-cpu graphs).
For walking a stack, this helper is an improvement over
bpf_probe_read(), which can be used with unrolled loops
but is not efficient and consumes a lot of eBPF instruc-
tions. Instead, bpf_get_stackid() can collect up to
PERF_MAX_STACK_DEPTH both kernel and user frames. Note
that this limit can be controlled with the sysctl pro-
gram, and that it should be manually increased in order
to profile long user stacks (such as stacks for Java pro-
grams). To do so, use:
# sysctl kernel.perf_event_max_stack=<new value>
Return The positive or null stack id on success, or a negative
error in case of failure.
s64 bpf_csum_diff(__be32 *from, u32 from_size, __be32 *to, u32 to_size,
__wsum seed)
Description
Compute a checksum difference, from the raw buffer
pointed by from, of length from_size (that must be a mul-
tiple of 4), towards the raw buffer pointed by to, of
size to_size (same remark). An optional seed can be added
to the value (this can be cascaded, the seed may come
from a previous call to the helper).
This is flexible enough to be used in several ways:
• With from_size == 0, to_size > 0 and seed set to check-
sum, it can be used when pushing new data.
• With from_size > 0, to_size == 0 and seed set to check-
sum, it can be used when removing data from a packet.
• With from_size > 0, to_size > 0 and seed set to 0, it
can be used to compute a diff. Note that from_size and
to_size do not need to be equal.
This helper can be used in combination with
bpf_l3_csum_replace() and bpf_l4_csum_replace(), to which
one can feed in the difference computed with
bpf_csum_diff().
Return The checksum result, or a negative error code in case of
failure.
long bpf_skb_get_tunnel_opt(struct sk_buff *skb, void *opt, u32 size)
Description
Retrieve tunnel options metadata for the packet associ-
ated to skb, and store the raw tunnel option data to the
buffer opt of size.
This helper can be used with encapsulation devices that
can operate in "collect metadata" mode (please refer to
the related note in the description of bpf_skb_get_tun-
nel_key() for more details). A particular example where
this can be used is in combination with the Geneve encap-
sulation protocol, where it allows for pushing (with
bpf_skb_get_tunnel_opt() helper) and retrieving arbitrary
TLVs (Type-Length-Value headers) from the eBPF program.
This allows for full customization of these headers.
Return The size of the option data retrieved.
long bpf_skb_set_tunnel_opt(struct sk_buff *skb, void *opt, u32 size)
Description
Set tunnel options metadata for the packet associated to
skb to the option data contained in the raw buffer opt of
size.
See also the description of the bpf_skb_get_tunnel_opt()
helper for additional information.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_change_proto(struct sk_buff *skb, __be16 proto, u64 flags)
Description
Change the protocol of the skb to proto. Currently sup-
ported are transition from IPv4 to IPv6, and from IPv6 to
IPv4. The helper takes care of the groundwork for the
transition, including resizing the socket buffer. The
eBPF program is expected to fill the new headers, if any,
via skb_store_bytes() and to recompute the checksums with
bpf_l3_csum_replace() and bpf_l4_csum_replace(). The main
case for this helper is to perform NAT64 operations out
of an eBPF program.
Internally, the GSO type is marked as dodgy so that head-
ers are checked and segments are recalculated by the
GSO/GRO engine. The size for GSO target is adapted as
well.
All values for flags are reserved for future usage, and
must be left at zero.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_change_type(struct sk_buff *skb, u32 type)
Description
Change the packet type for the packet associated to skb.
This comes down to setting skb->pkt_type to type, except
the eBPF program does not have a write access to
skb->pkt_type beside this helper. Using a helper here al-
lows for graceful handling of errors.
The major use case is to change incoming skb*s to
**PACKET_HOST* in a programmatic way instead of having to
recirculate via redirect(..., BPF_F_INGRESS), for exam-
ple.
Note that type only allows certain values. At this time,
they are:
PACKET_HOST
Packet is for us.
PACKET_BROADCAST
Send packet to all.
PACKET_MULTICAST
Send packet to group.
PACKET_OTHERHOST
Send packet to someone else.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_under_cgroup(struct sk_buff *skb, struct bpf_map *map, u32
index)
Description
Check whether skb is a descendant of the cgroup2 held by
map of type BPF_MAP_TYPE_CGROUP_ARRAY, at index.
Return The return value depends on the result of the test, and
can be:
• 0, if the skb failed the cgroup2 descendant test.
• 1, if the skb succeeded the cgroup2 descendant test.
• A negative error code, if an error occurred.
u32 bpf_get_hash_recalc(struct sk_buff *skb)
Description
Retrieve the hash of the packet, skb->hash. If it is not
set, in particular if the hash was cleared due to man-
gling, recompute this hash. Later accesses to the hash
can be done directly with skb->hash.
Calling bpf_set_hash_invalid(), changing a packet proto-
type with bpf_skb_change_proto(), or calling
bpf_skb_store_bytes() with the BPF_F_INVALIDATE_HASH are
actions susceptible to clear the hash and to trigger a
new computation for the next call to bpf_get_hash_re-
calc().
Return The 32-bit hash.
u64 bpf_get_current_task(void)
Description
Get the current task.
Return A pointer to the current task struct.
long bpf_probe_write_user(void *dst, const void *src, u32 len)
Description
Attempt in a safe way to write len bytes from the buffer
src to dst in memory. It only works for threads that are
in user context, and dst must be a valid user space ad-
dress.
This helper should not be used to implement any kind of
security mechanism because of TOC-TOU attacks, but rather
to debug, divert, and manipulate execution of semi-coop-
erative processes.
Keep in mind that this feature is meant for experiments,
and it has a risk of crashing the system and running pro-
grams. Therefore, when an eBPF program using this helper
is attached, a warning including PID and process name is
printed to kernel logs.
Return 0 on success, or a negative error in case of failure.
long bpf_current_task_under_cgroup(struct bpf_map *map, u32 index)
Description
Check whether the probe is being run is the context of a
given subset of the cgroup2 hierarchy. The cgroup2 to
test is held by map of type BPF_MAP_TYPE_CGROUP_ARRAY, at
index.
Return The return value depends on the result of the test, and
can be:
• 1, if current task belongs to the cgroup2.
• 0, if current task does not belong to the cgroup2.
• A negative error code, if an error occurred.
long bpf_skb_change_tail(struct sk_buff *skb, u32 len, u64 flags)
Description
Resize (trim or grow) the packet associated to skb to the
new len. The flags are reserved for future usage, and
must be left at zero.
The basic idea is that the helper performs the needed
work to change the size of the packet, then the eBPF pro-
gram rewrites the rest via helpers like
bpf_skb_store_bytes(), bpf_l3_csum_replace(),
bpf_l3_csum_replace() and others. This helper is a slow
path utility intended for replies with control messages.
And because it is targeted for slow path, the helper it-
self can afford to be slow: it implicitly linearizes, un-
clones and drops offloads from the skb.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_pull_data(struct sk_buff *skb, u32 len)
Description
Pull in non-linear data in case the skb is non-linear and
not all of len are part of the linear section. Make len
bytes from skb readable and writable. If a zero value is
passed for len, then all bytes in the linear part of skb
will be made readable and writable.
This helper is only needed for reading and writing with
direct packet access.
For direct packet access, testing that offsets to access
are within packet boundaries (test on skb->data_end) is
susceptible to fail if offsets are invalid, or if the re-
quested data is in non-linear parts of the skb. On fail-
ure the program can just bail out, or in the case of a
non-linear buffer, use a helper to make the data avail-
able. The bpf_skb_load_bytes() helper is a first solution
to access the data. Another one consists in using
bpf_skb_pull_data to pull in once the non-linear parts,
then retesting and eventually access the data.
At the same time, this also makes sure the skb is un-
cloned, which is a necessary condition for direct write.
As this needs to be an invariant for the write part only,
the verifier detects writes and adds a prologue that is
calling bpf_skb_pull_data() to effectively unclone the
skb from the very beginning in case it is indeed cloned.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
s64 bpf_csum_update(struct sk_buff *skb, __wsum csum)
Description
Add the checksum csum into skb->csum in case the driver
has supplied a checksum for the entire packet into that
field. Return an error otherwise. This helper is intended
to be used in combination with bpf_csum_diff(), in par-
ticular when the checksum needs to be updated after data
has been written into the packet through direct packet
access.
Return The checksum on success, or a negative error code in case
of failure.
void bpf_set_hash_invalid(struct sk_buff *skb)
Description
Invalidate the current skb->hash. It can be used after
mangling on headers through direct packet access, in or-
der to indicate that the hash is outdated and to trigger
a recalculation the next time the kernel tries to access
this hash or when the bpf_get_hash_recalc() helper is
called.
Return void.
long bpf_get_numa_node_id(void)
Description
Return the id of the current NUMA node. The primary use
case for this helper is the selection of sockets for the
local NUMA node, when the program is attached to sockets
using the SO_ATTACH_REUSEPORT_EBPF option (see also
socket(7)), but the helper is also available to other
eBPF program types, similarly to bpf_get_smp_proces-
sor_id().
Return The id of current NUMA node.
long bpf_skb_change_head(struct sk_buff *skb, u32 len, u64 flags)
Description
Grows headroom of packet associated to skb and adjusts
the offset of the MAC header accordingly, adding len
bytes of space. It automatically extends and reallocates
memory as required.
This helper can be used on a layer 3 skb to push a MAC
header for redirection into a layer 2 device.
All values for flags are reserved for future usage, and
must be left at zero.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_xdp_adjust_head(struct xdp_buff *xdp_md, int delta)
Description
Adjust (move) xdp_md->data by delta bytes. Note that it
is possible to use a negative value for delta. This
helper can be used to prepare the packet for pushing or
popping headers.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_probe_read_str(void *dst, u32 size, const void *unsafe_ptr)
Description
Copy a NUL terminated string from an unsafe kernel ad-
dress unsafe_ptr to dst. See bpf_probe_read_kernel_str()
for more details.
Generally, use bpf_probe_read_user_str() or
bpf_probe_read_kernel_str() instead.
Return On success, the strictly positive length of the string,
including the trailing NUL character. On error, a nega-
tive value.
u64 bpf_get_socket_cookie(struct sk_buff *skb)
Description
If the struct sk_buff pointed by skb has a known socket,
retrieve the cookie (generated by the kernel) of this
socket. If no cookie has been set yet, generate a new
cookie. Once generated, the socket cookie remains stable
for the life of the socket. This helper can be useful for
monitoring per socket networking traffic statistics as it
provides a global socket identifier that can be assumed
unique.
Return A 8-byte long unique number on success, or 0 if the
socket field is missing inside skb.
u64 bpf_get_socket_cookie(struct bpf_sock_addr *ctx)
Description
Equivalent to bpf_get_socket_cookie() helper that accepts
skb, but gets socket from struct bpf_sock_addr context.
Return A 8-byte long unique number.
u64 bpf_get_socket_cookie(struct bpf_sock_ops *ctx)
Description
Equivalent to bpf_get_socket_cookie() helper that accepts
skb, but gets socket from struct bpf_sock_ops context.
Return A 8-byte long unique number.
u64 bpf_get_socket_cookie(struct sock *sk)
Description
Equivalent to bpf_get_socket_cookie() helper that accepts
sk, but gets socket from a BTF struct sock. This helper
also works for sleepable programs.
Return A 8-byte long unique number or 0 if sk is NULL.
u32 bpf_get_socket_uid(struct sk_buff *skb)
Description
Get the owner UID of the socked associated to skb.
Return The owner UID of the socket associated to skb. If the
socket is NULL, or if it is not a full socket (i.e. if it
is a time-wait or a request socket instead), overflowuid
value is returned (note that overflowuid might also be
the actual UID value for the socket).
long bpf_set_hash(struct sk_buff *skb, u32 hash)
Description
Set the full hash for skb (set the field skb->hash) to
value hash.
Return 0
long bpf_setsockopt(void *bpf_socket, int level, int optname, void
*optval, int optlen)
Description
Emulate a call to setsockopt() on the socket associated
to bpf_socket, which must be a full socket. The level at
which the option resides and the name optname of the op-
tion must be specified, see setsockopt(2) for more infor-
mation. The option value of length optlen is pointed by
optval.
bpf_socket should be one of the following:
• struct bpf_sock_ops for BPF_PROG_TYPE_SOCK_OPS.
• struct bpf_sock_addr for BPF_CGROUP_INET4_CONNECT,
BPF_CGROUP_INET6_CONNECT and BPF_CGROUP_UNIX_CONNECT.
This helper actually implements a subset of setsockopt().
It supports the following levels:
• SOL_SOCKET, which supports the following optnames:
SO_RCVBUF, SO_SNDBUF, SO_MAX_PACING_RATE, SO_PRIORITY,
SO_RCVLOWAT, SO_MARK, SO_BINDTODEVICE, SO_KEEPALIVE,
SO_REUSEADDR, SO_REUSEPORT, SO_BINDTOIFINDEX, SO_TXRE-
HASH.
• IPPROTO_TCP, which supports the following optnames:
TCP_CONGESTION, TCP_BPF_IW, TCP_BPF_SNDCWND_CLAMP,
TCP_SAVE_SYN, TCP_KEEPIDLE, TCP_KEEPINTVL, TCP_KEEPCNT,
TCP_SYNCNT, TCP_USER_TIMEOUT, TCP_NOTSENT_LOWAT,
TCP_NODELAY, TCP_MAXSEG, TCP_WINDOW_CLAMP,
TCP_THIN_LINEAR_TIMEOUTS, TCP_BPF_DELACK_MAX,
TCP_BPF_RTO_MIN.
• IPPROTO_IP, which supports optname IP_TOS.
• IPPROTO_IPV6, which supports the following optnames:
IPV6_TCLASS, IPV6_AUTOFLOWLABEL.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_adjust_room(struct sk_buff *skb, s32 len_diff, u32 mode,
u64 flags)
Description
Grow or shrink the room for data in the packet associated
to skb by len_diff, and according to the selected mode.
By default, the helper will reset any offloaded checksum
indicator of the skb to CHECKSUM_NONE. This can be
avoided by the following flag:
• BPF_F_ADJ_ROOM_NO_CSUM_RESET: Do not reset offloaded
checksum data of the skb to CHECKSUM_NONE.
There are two supported modes at this time:
• BPF_ADJ_ROOM_MAC: Adjust room at the mac layer (room
space is added or removed between the layer 2 and layer
3 headers).
• BPF_ADJ_ROOM_NET: Adjust room at the network layer
(room space is added or removed between the layer 3 and
layer 4 headers).
The following flags are supported at this time:
• BPF_F_ADJ_ROOM_FIXED_GSO: Do not adjust gso_size. Ad-
justing mss in this way is not allowed for datagrams.
• BPF_F_ADJ_ROOM_ENCAP_L3_IPV4, BPF_F_ADJ_ROOM_EN-
CAP_L3_IPV6: Any new space is reserved to hold a tunnel
header. Configure skb offsets and other fields accord-
ingly.
• BPF_F_ADJ_ROOM_ENCAP_L4_GRE, BPF_F_ADJ_ROOM_EN-
CAP_L4_UDP: Use with ENCAP_L3 flags to further specify
the tunnel type.
• BPF_F_ADJ_ROOM_ENCAP_L2(len): Use with ENCAP_L3/L4
flags to further specify the tunnel type; len is the
length of the inner MAC header.
• BPF_F_ADJ_ROOM_ENCAP_L2_ETH: Use with
BPF_F_ADJ_ROOM_ENCAP_L2 flag to further specify the L2
type as Ethernet.
• BPF_F_ADJ_ROOM_DECAP_L3_IPV4, BPF_F_ADJ_ROOM_DE-
CAP_L3_IPV6: Indicate the new IP header version after
decapsulating the outer IP header. Used when the inner
and outer IP versions are different.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_redirect_map(struct bpf_map *map, u64 key, u64 flags)
Description
Redirect the packet to the endpoint referenced by map at
index key. Depending on its type, this map can contain
references to net devices (for forwarding packets through
other ports), or to CPUs (for redirecting XDP frames to
another CPU; but this is only implemented for native XDP
(with driver support) as of this writing).
The lower two bits of flags are used as the return code
if the map lookup fails. This is so that the return value
can be one of the XDP program return codes up to XDP_TX,
as chosen by the caller. The higher bits of flags can be
set to BPF_F_BROADCAST or BPF_F_EXCLUDE_INGRESS as de-
fined below.
With BPF_F_BROADCAST the packet will be broadcasted to
all the interfaces in the map, with BPF_F_EXCLUDE_INGRESS
the ingress interface will be excluded when do broadcast-
ing.
See also bpf_redirect(), which only supports redirecting
to an ifindex, but doesn't require a map to do so.
Return XDP_REDIRECT on success, or the value of the two lower
bits of the flags argument on error.
long bpf_sk_redirect_map(struct sk_buff *skb, struct bpf_map *map, u32
key, u64 flags)
Description
Redirect the packet to the socket referenced by map (of
type BPF_MAP_TYPE_SOCKMAP) at index key. Both ingress and
egress interfaces can be used for redirection. The
BPF_F_INGRESS value in flags is used to make the distinc-
tion (ingress path is selected if the flag is present,
egress path otherwise). This is the only flag supported
for now.
Return SK_PASS on success, or SK_DROP on error.
long bpf_sock_map_update(struct bpf_sock_ops *skops, struct bpf_map
*map, void *key, u64 flags)
Description
Add an entry to, or update a map referencing sockets. The
skops is used as a new value for the entry associated to
key. flags is one of:
BPF_NOEXIST
The entry for key must not exist in the map.
BPF_EXIST
The entry for key must already exist in the map.
BPF_ANY
No condition on the existence of the entry for
key.
If the map has eBPF programs (parser and verdict), those
will be inherited by the socket being added. If the
socket is already attached to eBPF programs, this results
in an error.
Return 0 on success, or a negative error in case of failure.
long bpf_xdp_adjust_meta(struct xdp_buff *xdp_md, int delta)
Description
Adjust the address pointed by xdp_md->data_meta by delta
(which can be positive or negative). Note that this oper-
ation modifies the address stored in xdp_md->data, so the
latter must be loaded only after the helper has been
called.
The use of xdp_md->data_meta is optional and programs are
not required to use it. The rationale is that when the
packet is processed with XDP (e.g. as DoS filter), it is
possible to push further meta data along with it before
passing to the stack, and to give the guarantee that an
ingress eBPF program attached as a TC classifier on the
same device can pick this up for further post-processing.
Since TC works with socket buffers, it remains possible
to set from XDP the mark or priority pointers, or other
pointers for the socket buffer. Having this scratch
space generic and programmable allows for more flexibil-
ity as the user is free to store whatever meta data they
need.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_perf_event_read_value(struct bpf_map *map, u64 flags, struct
bpf_perf_event_value *buf, u32 buf_size)
Description
Read the value of a perf event counter, and store it into
buf of size buf_size. This helper relies on a map of type
BPF_MAP_TYPE_PERF_EVENT_ARRAY. The nature of the perf
event counter is selected when map is updated with perf
event file descriptors. The map is an array whose size is
the number of available CPUs, and each cell contains a
value relative to one CPU. The value to retrieve is indi-
cated by flags, that contains the index of the CPU to
look up, masked with BPF_F_INDEX_MASK. Alternatively,
flags can be set to BPF_F_CURRENT_CPU to indicate that
the value for the current CPU should be retrieved.
This helper behaves in a way close to
bpf_perf_event_read() helper, save that instead of just
returning the value observed, it fills the buf structure.
This allows for additional data to be retrieved: in par-
ticular, the enabled and running times (in buf->enabled
and buf->running, respectively) are copied. In general,
bpf_perf_event_read_value() is recommended over
bpf_perf_event_read(), which has some ABI issues and pro-
vides fewer functionalities.
These values are interesting, because hardware PMU (Per-
formance Monitoring Unit) counters are limited resources.
When there are more PMU based perf events opened than
available counters, kernel will multiplex these events so
each event gets certain percentage (but not all) of the
PMU time. In case that multiplexing happens, the number
of samples or counter value will not reflect the case
compared to when no multiplexing occurs. This makes com-
parison between different runs difficult. Typically, the
counter value should be normalized before comparing to
other experiments. The usual normalization is done as
follows.
normalized_counter = counter * t_enabled / t_running
Where t_enabled is the time enabled for event and t_run-
ning is the time running for event since last normaliza-
tion. The enabled and running times are accumulated since
the perf event open. To achieve scaling factor between
two invocations of an eBPF program, users can use CPU id
as the key (which is typical for perf array usage model)
to remember the previous value and do the calculation in-
side the eBPF program.
Return 0 on success, or a negative error in case of failure.
long bpf_perf_prog_read_value(struct bpf_perf_event_data *ctx, struct
bpf_perf_event_value *buf, u32 buf_size)
Description
For an eBPF program attached to a perf event, retrieve
the value of the event counter associated to ctx and
store it in the structure pointed by buf and of size
buf_size. Enabled and running times are also stored in
the structure (see description of helper
bpf_perf_event_read_value() for more details).
Return 0 on success, or a negative error in case of failure.
long bpf_getsockopt(void *bpf_socket, int level, int optname, void
*optval, int optlen)
Description
Emulate a call to getsockopt() on the socket associated
to bpf_socket, which must be a full socket. The level at
which the option resides and the name optname of the op-
tion must be specified, see getsockopt(2) for more infor-
mation. The retrieved value is stored in the structure
pointed by opval and of length optlen.
bpf_socket should be one of the following:
• struct bpf_sock_ops for BPF_PROG_TYPE_SOCK_OPS.
• struct bpf_sock_addr for BPF_CGROUP_INET4_CONNECT,
BPF_CGROUP_INET6_CONNECT and BPF_CGROUP_UNIX_CONNECT.
This helper actually implements a subset of getsockopt().
It supports the same set of optnames that is supported by
the bpf_setsockopt() helper. The exceptions are
TCP_BPF_* is bpf_setsockopt() only and TCP_SAVED_SYN is
bpf_getsockopt() only.
Return 0 on success, or a negative error in case of failure.
long bpf_override_return(struct pt_regs *regs, u64 rc)
Description
Used for error injection, this helper uses kprobes to
override the return value of the probed function, and to
set it to rc. The first argument is the context regs on
which the kprobe works.
This helper works by setting the PC (program counter) to
an override function which is run in place of the origi-
nal probed function. This means the probed function is
not run at all. The replacement function just returns
with the required value.
This helper has security implications, and thus is sub-
ject to restrictions. It is only available if the kernel
was compiled with the CONFIG_BPF_KPROBE_OVERRIDE configu-
ration option, and in this case it only works on func-
tions tagged with ALLOW_ERROR_INJECTION in the kernel
code.
Also, the helper is only available for the architectures
having the CONFIG_FUNCTION_ERROR_INJECTION option. As of
this writing, x86 architecture is the only one to support
this feature.
Return 0
long bpf_sock_ops_cb_flags_set(struct bpf_sock_ops *bpf_sock, int
argval)
Description
Attempt to set the value of the bpf_sock_ops_cb_flags
field for the full TCP socket associated to bpf_sock_ops
to argval.
The primary use of this field is to determine if there
should be calls to eBPF programs of type
BPF_PROG_TYPE_SOCK_OPS at various points in the TCP code.
A program of the same type can change its value, per con-
nection and as necessary, when the connection is estab-
lished. This field is directly accessible for reading,
but this helper must be used for updates in order to re-
turn an error if an eBPF program tries to set a callback
that is not supported in the current kernel.
argval is a flag array which can combine these flags:
• BPF_SOCK_OPS_RTO_CB_FLAG (retransmission time out)
• BPF_SOCK_OPS_RETRANS_CB_FLAG (retransmission)
• BPF_SOCK_OPS_STATE_CB_FLAG (TCP state change)
• BPF_SOCK_OPS_RTT_CB_FLAG (every RTT)
Therefore, this function can be used to clear a callback
flag by setting the appropriate bit to zero. e.g. to dis-
able the RTO callback:
bpf_sock_ops_cb_flags_set(bpf_sock,
bpf_sock->bpf_sock_ops_cb_flags &
~BPF_SOCK_OPS_RTO_CB_FLAG)
Here are some examples of where one could call such eBPF
program:
• When RTO fires.
• When a packet is retransmitted.
• When the connection terminates.
• When a packet is sent.
• When a packet is received.
Return Code -EINVAL if the socket is not a full TCP socket; oth-
erwise, a positive number containing the bits that could
not be set is returned (which comes down to 0 if all bits
were set as required).
long bpf_msg_redirect_map(struct sk_msg_buff *msg, struct bpf_map *map,
u32 key, u64 flags)
Description
This helper is used in programs implementing policies at
the socket level. If the message msg is allowed to pass
(i.e. if the verdict eBPF program returns SK_PASS), redi-
rect it to the socket referenced by map (of type
BPF_MAP_TYPE_SOCKMAP) at index key. Both ingress and
egress interfaces can be used for redirection. The
BPF_F_INGRESS value in flags is used to make the distinc-
tion (ingress path is selected if the flag is present,
egress path otherwise). This is the only flag supported
for now.
Return SK_PASS on success, or SK_DROP on error.
long bpf_msg_apply_bytes(struct sk_msg_buff *msg, u32 bytes)
Description
For socket policies, apply the verdict of the eBPF pro-
gram to the next bytes (number of bytes) of message msg.
For example, this helper can be used in the following
cases:
• A single sendmsg() or sendfile() system call contains
multiple logical messages that the eBPF program is sup-
posed to read and for which it should apply a verdict.
• An eBPF program only cares to read the first bytes of a
msg. If the message has a large payload, then setting
up and calling the eBPF program repeatedly for all
bytes, even though the verdict is already known, would
create unnecessary overhead.
When called from within an eBPF program, the helper sets
a counter internal to the BPF infrastructure, that is
used to apply the last verdict to the next bytes. If
bytes is smaller than the current data being processed
from a sendmsg() or sendfile() system call, the first
bytes will be sent and the eBPF program will be re-run
with the pointer for start of data pointing to byte num-
ber bytes + 1. If bytes is larger than the current data
being processed, then the eBPF verdict will be applied to
multiple sendmsg() or sendfile() calls until bytes are
consumed.
Note that if a socket closes with the internal counter
holding a non-zero value, this is not a problem because
data is not being buffered for bytes and is sent as it is
received.
Return 0
long bpf_msg_cork_bytes(struct sk_msg_buff *msg, u32 bytes)
Description
For socket policies, prevent the execution of the verdict
eBPF program for message msg until bytes (byte number)
have been accumulated.
This can be used when one needs a specific number of
bytes before a verdict can be assigned, even if the data
spans multiple sendmsg() or sendfile() calls. The extreme
case would be a user calling sendmsg() repeatedly with
1-byte long message segments. Obviously, this is bad for
performance, but it is still valid. If the eBPF program
needs bytes bytes to validate a header, this helper can
be used to prevent the eBPF program to be called again
until bytes have been accumulated.
Return 0
long bpf_msg_pull_data(struct sk_msg_buff *msg, u32 start, u32 end, u64
flags)
Description
For socket policies, pull in non-linear data from user
space for msg and set pointers msg->data and
msg->data_end to start and end bytes offsets into msg,
respectively.
If a program of type BPF_PROG_TYPE_SK_MSG is run on a msg
it can only parse data that the (data, data_end) pointers
have already consumed. For sendmsg() hooks this is likely
the first scatterlist element. But for calls relying on
the sendpage handler (e.g. sendfile()) this will be the
range (0, 0) because the data is shared with user space
and by default the objective is to avoid allowing user
space to modify data while (or after) eBPF verdict is be-
ing decided. This helper can be used to pull in data and
to set the start and end pointer to given values. Data
will be copied if necessary (i.e. if data was not linear
and if start and end pointers do not point to the same
chunk).
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
All values for flags are reserved for future usage, and
must be left at zero.
Return 0 on success, or a negative error in case of failure.
long bpf_bind(struct bpf_sock_addr *ctx, struct sockaddr *addr, int
addr_len)
Description
Bind the socket associated to ctx to the address pointed
by addr, of length addr_len. This allows for making out-
going connection from the desired IP address, which can
be useful for example when all processes inside a cgroup
should use one single IP address on a host that has mul-
tiple IP configured.
This helper works for IPv4 and IPv6, TCP and UDP sockets.
The domain (addr->sa_family) must be AF_INET (or
AF_INET6). It's advised to pass zero port (sin_port or
sin6_port) which triggers IP_BIND_ADDRESS_NO_PORT-like
behavior and lets the kernel efficiently pick up an un-
used port as long as 4-tuple is unique. Passing non-zero
port might lead to degraded performance.
Return 0 on success, or a negative error in case of failure.
long bpf_xdp_adjust_tail(struct xdp_buff *xdp_md, int delta)
Description
Adjust (move) xdp_md->data_end by delta bytes. It is pos-
sible to both shrink and grow the packet tail. Shrink
done via delta being a negative integer.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_skb_get_xfrm_state(struct sk_buff *skb, u32 index, struct
bpf_xfrm_state *xfrm_state, u32 size, u64 flags)
Description
Retrieve the XFRM state (IP transform framework, see also
ip-xfrm(8)) at index in XFRM "security path" for skb.
The retrieved value is stored in the struct
bpf_xfrm_state pointed by xfrm_state and of length size.
All values for flags are reserved for future usage, and
must be left at zero.
This helper is available only if the kernel was compiled
with CONFIG_XFRM configuration option.
Return 0 on success, or a negative error in case of failure.
long bpf_get_stack(void *ctx, void *buf, u32 size, u64 flags)
Description
Return a user or a kernel stack in bpf program provided
buffer. To achieve this, the helper needs ctx, which is
a pointer to the context on which the tracing program is
executed. To store the stacktrace, the bpf program pro-
vides buf with a nonnegative size.
The last argument, flags, holds the number of stack
frames to skip (from 0 to 255), masked with
BPF_F_SKIP_FIELD_MASK. The next bits can be used to set
the following flags:
BPF_F_USER_STACK
Collect a user space stack instead of a kernel
stack.
BPF_F_USER_BUILD_ID
Collect (build_id, file_offset) instead of ips for
user stack, only valid if BPF_F_USER_STACK is also
specified.
file_offset is an offset relative to the beginning
of the executable or shared object file backing
the vma which the ip falls in. It is not an offset
relative to that object's base address. Accord-
ingly, it must be adjusted by adding (sh_addr -
sh_offset), where sh_{addr,offset} correspond to
the executable section containing file_offset in
the object, for comparisons to symbols' st_value
to be valid.
bpf_get_stack() can collect up to PERF_MAX_STACK_DEPTH
both kernel and user frames, subject to sufficient large
buffer size. Note that this limit can be controlled with
the sysctl program, and that it should be manually in-
creased in order to profile long user stacks (such as
stacks for Java programs). To do so, use:
# sysctl kernel.perf_event_max_stack=<new value>
Return The non-negative copied buf length equal to or less than
size on success, or a negative error in case of failure.
long bpf_skb_load_bytes_relative(const void *skb, u32 offset, void *to,
u32 len, u32 start_header)
Description
This helper is similar to bpf_skb_load_bytes() in that it
provides an easy way to load len bytes from offset from
the packet associated to skb, into the buffer pointed by
to. The difference to bpf_skb_load_bytes() is that a
fifth argument start_header exists in order to select a
base offset to start from. start_header can be one of:
BPF_HDR_START_MAC
Base offset to load data from is skb's mac header.
BPF_HDR_START_NET
Base offset to load data from is skb's network
header.
In general, "direct packet access" is the preferred
method to access packet data, however, this helper is in
particular useful in socket filters where skb->data does
not always point to the start of the mac header and where
"direct packet access" is not available.
Return 0 on success, or a negative error in case of failure.
long bpf_fib_lookup(void *ctx, struct bpf_fib_lookup *params, int plen,
u32 flags)
Description
Do FIB lookup in kernel tables using parameters in
params. If lookup is successful and result shows packet
is to be forwarded, the neighbor tables are searched for
the nexthop. If successful (ie., FIB lookup shows for-
warding and nexthop is resolved), the nexthop address is
returned in ipv4_dst or ipv6_dst based on family, smac is
set to mac address of egress device, dmac is set to nex-
thop mac address, rt_metric is set to metric from route
(IPv4/IPv6 only), and ifindex is set to the device index
of the nexthop from the FIB lookup.
plen argument is the size of the passed in struct. flags
argument can be a combination of one or more of the fol-
lowing values:
BPF_FIB_LOOKUP_DIRECT
Do a direct table lookup vs full lookup using FIB
rules.
BPF_FIB_LOOKUP_TBID
Used with BPF_FIB_LOOKUP_DIRECT. Use the routing
table ID present in params->tbid for the fib
lookup.
BPF_FIB_LOOKUP_OUTPUT
Perform lookup from an egress perspective (default
is ingress).
BPF_FIB_LOOKUP_SKIP_NEIGH
Skip the neighbour table lookup. params->dmac and
params->smac will not be set as output. A common
use case is to call bpf_redirect_neigh() after do-
ing bpf_fib_lookup().
BPF_FIB_LOOKUP_SRC
Derive and set source IP addr in
params->ipv{4,6}_src for the nexthop. If the src
addr cannot be derived,
BPF_FIB_LKUP_RET_NO_SRC_ADDR is returned. In this
case, params->dmac and params->smac are not set
either.
ctx is either struct xdp_md for XDP programs or struct
sk_buff tc cls_act programs.
Return
• < 0 if any input argument is invalid
• 0 on success (packet is forwarded, nexthop neighbor ex-
ists)
• > 0 one of BPF_FIB_LKUP_RET_ codes explaining why the
packet is not forwarded or needs assist from full stack
If lookup fails with BPF_FIB_LKUP_RET_FRAG_NEEDED, then
the MTU was exceeded and output params->mtu_result con-
tains the MTU.
long bpf_sock_hash_update(struct bpf_sock_ops *skops, struct bpf_map
*map, void *key, u64 flags)
Description
Add an entry to, or update a sockhash map referencing
sockets. The skops is used as a new value for the entry
associated to key. flags is one of:
BPF_NOEXIST
The entry for key must not exist in the map.
BPF_EXIST
The entry for key must already exist in the map.
BPF_ANY
No condition on the existence of the entry for
key.
If the map has eBPF programs (parser and verdict), those
will be inherited by the socket being added. If the
socket is already attached to eBPF programs, this results
in an error.
Return 0 on success, or a negative error in case of failure.
long bpf_msg_redirect_hash(struct sk_msg_buff *msg, struct bpf_map
*map, void *key, u64 flags)
Description
This helper is used in programs implementing policies at
the socket level. If the message msg is allowed to pass
(i.e. if the verdict eBPF program returns SK_PASS), redi-
rect it to the socket referenced by map (of type
BPF_MAP_TYPE_SOCKHASH) using hash key. Both ingress and
egress interfaces can be used for redirection. The
BPF_F_INGRESS value in flags is used to make the distinc-
tion (ingress path is selected if the flag is present,
egress path otherwise). This is the only flag supported
for now.
Return SK_PASS on success, or SK_DROP on error.
long bpf_sk_redirect_hash(struct sk_buff *skb, struct bpf_map *map,
void *key, u64 flags)
Description
This helper is used in programs implementing policies at
the skb socket level. If the sk_buff skb is allowed to
pass (i.e. if the verdict eBPF program returns SK_PASS),
redirect it to the socket referenced by map (of type
BPF_MAP_TYPE_SOCKHASH) using hash key. Both ingress and
egress interfaces can be used for redirection. The
BPF_F_INGRESS value in flags is used to make the distinc-
tion (ingress path is selected if the flag is present,
egress otherwise). This is the only flag supported for
now.
Return SK_PASS on success, or SK_DROP on error.
long bpf_lwt_push_encap(struct sk_buff *skb, u32 type, void *hdr, u32
len)
Description
Encapsulate the packet associated to skb within a Layer 3
protocol header. This header is provided in the buffer at
address hdr, with len its size in bytes. type indicates
the protocol of the header and can be one of:
BPF_LWT_ENCAP_SEG6
IPv6 encapsulation with Segment Routing Header
(struct ipv6_sr_hdr). hdr only contains the SRH,
the IPv6 header is computed by the kernel.
BPF_LWT_ENCAP_SEG6_INLINE
Only works if skb contains an IPv6 packet. Insert
a Segment Routing Header (struct ipv6_sr_hdr) in-
side the IPv6 header.
BPF_LWT_ENCAP_IP
IP encapsulation (GRE/GUE/IPIP/etc). The outer
header must be IPv4 or IPv6, followed by zero or
more additional headers, up to LWT_BPF_MAX_HEAD-
ROOM total bytes in all prepended headers. Please
note that if skb_is_gso(skb) is true, no more than
two headers can be prepended, and the inner
header, if present, should be either GRE or
UDP/GUE.
BPF_LWT_ENCAP_SEG6* types can be called by BPF programs
of type BPF_PROG_TYPE_LWT_IN; BPF_LWT_ENCAP_IP type can
be called by bpf programs of types BPF_PROG_TYPE_LWT_IN
and BPF_PROG_TYPE_LWT_XMIT.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_lwt_seg6_store_bytes(struct sk_buff *skb, u32 offset, const
void *from, u32 len)
Description
Store len bytes from address from into the packet associ-
ated to skb, at offset. Only the flags, tag and TLVs in-
side the outermost IPv6 Segment Routing Header can be
modified through this helper.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_lwt_seg6_adjust_srh(struct sk_buff *skb, u32 offset, s32
delta)
Description
Adjust the size allocated to TLVs in the outermost IPv6
Segment Routing Header contained in the packet associated
to skb, at position offset by delta bytes. Only offsets
after the segments are accepted. delta can be as well
positive (growing) as negative (shrinking).
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_lwt_seg6_action(struct sk_buff *skb, u32 action, void *param,
u32 param_len)
Description
Apply an IPv6 Segment Routing action of type action to
the packet associated to skb. Each action takes a parame-
ter contained at address param, and of length param_len
bytes. action can be one of:
SEG6_LOCAL_ACTION_END_X
End.X action: Endpoint with Layer-3 cross-connect.
Type of param: struct in6_addr.
SEG6_LOCAL_ACTION_END_T
End.T action: Endpoint with specific IPv6 table
lookup. Type of param: int.
SEG6_LOCAL_ACTION_END_B6
End.B6 action: Endpoint bound to an SRv6 policy.
Type of param: struct ipv6_sr_hdr.
SEG6_LOCAL_ACTION_END_B6_ENCAP
End.B6.Encap action: Endpoint bound to an SRv6 en-
capsulation policy. Type of param: struct
ipv6_sr_hdr.
A call to this helper is susceptible to change the under-
lying packet buffer. Therefore, at load time, all checks
on pointers previously done by the verifier are invali-
dated and must be performed again, if the helper is used
in combination with direct packet access.
Return 0 on success, or a negative error in case of failure.
long bpf_rc_repeat(void *ctx)
Description
This helper is used in programs implementing IR decoding,
to report a successfully decoded repeat key message. This
delays the generation of a key up event for previously
generated key down event.
Some IR protocols like NEC have a special IR message for
repeating last button, for when a button is held down.
The ctx should point to the lirc sample as passed into
the program.
This helper is only available is the kernel was compiled
with the CONFIG_BPF_LIRC_MODE2 configuration option set
to "y".
Return 0
long bpf_rc_keydown(void *ctx, u32 protocol, u64 scancode, u32 toggle)
Description
This helper is used in programs implementing IR decoding,
to report a successfully decoded key press with scancode,
toggle value in the given protocol. The scancode will be
translated to a keycode using the rc keymap, and reported
as an input key down event. After a period a key up event
is generated. This period can be extended by calling ei-
ther bpf_rc_keydown() again with the same values, or
calling bpf_rc_repeat().
Some protocols include a toggle bit, in case the button
was released and pressed again between consecutive scan-
codes.
The ctx should point to the lirc sample as passed into
the program.
The protocol is the decoded protocol number (see enum
rc_proto for some predefined values).
This helper is only available is the kernel was compiled
with the CONFIG_BPF_LIRC_MODE2 configuration option set
to "y".
Return 0
u64 bpf_skb_cgroup_id(struct sk_buff *skb)
Description
Return the cgroup v2 id of the socket associated with the
skb. This is roughly similar to the bpf_get_cgroup_clas-
sid() helper for cgroup v1 by providing a tag resp. iden-
tifier that can be matched on or used for map lookups
e.g. to implement policy. The cgroup v2 id of a given
path in the hierarchy is exposed in user space through
the f_handle API in order to get to the same 64-bit id.
This helper can be used on TC egress path, but not on
ingress, and is available only if the kernel was compiled
with the CONFIG_SOCK_CGROUP_DATA configuration option.
Return The id is returned or 0 in case the id could not be re-
trieved.
u64 bpf_get_current_cgroup_id(void)
Description
Get the current cgroup id based on the cgroup within
which the current task is running.
Return A 64-bit integer containing the current cgroup id based
on the cgroup within which the current task is running.
void *bpf_get_local_storage(void *map, u64 flags)
Description
Get the pointer to the local storage area. The type and
the size of the local storage is defined by the map argu-
ment. The flags meaning is specific for each map type,
and has to be 0 for cgroup local storage.
Depending on the BPF program type, a local storage area
can be shared between multiple instances of the BPF pro-
gram, running simultaneously.
A user should care about the synchronization by himself.
For example, by using the BPF_ATOMIC instructions to al-
ter the shared data.
Return A pointer to the local storage area.
long bpf_sk_select_reuseport(struct sk_reuseport_md *reuse, struct
bpf_map *map, void *key, u64 flags)
Description
Select a SO_REUSEPORT socket from a BPF_MAP_TYPE_REUSE-
PORT_SOCKARRAY map. It checks the selected socket is
matching the incoming request in the socket buffer.
Return 0 on success, or a negative error in case of failure.
u64 bpf_skb_ancestor_cgroup_id(struct sk_buff *skb, int ancestor_level)
Description
Return id of cgroup v2 that is ancestor of cgroup associ-
ated with the skb at the ancestor_level. The root cgroup
is at ancestor_level zero and each step down the hierar-
chy increments the level. If ancestor_level == level of
cgroup associated with skb, then return value will be
same as that of bpf_skb_cgroup_id().
The helper is useful to implement policies based on
cgroups that are upper in hierarchy than immediate cgroup
associated with skb.
The format of returned id and helper limitations are same
as in bpf_skb_cgroup_id().
Return The id is returned or 0 in case the id could not be re-
trieved.
struct bpf_sock *bpf_sk_lookup_tcp(void *ctx, struct bpf_sock_tuple
*tuple, u32 tuple_size, u64 netns, u64 flags)
Description
Look for TCP socket matching tuple, optionally in a child
network namespace netns. The return value must be
checked, and if non-NULL, released via bpf_sk_release().
The ctx should point to the context of the program, such
as the skb or socket (depending on the hook in use). This
is used to determine the base network namespace for the
lookup.
tuple_size must be one of:
sizeof(tuple->ipv4)
Look for an IPv4 socket.
sizeof(tuple->ipv6)
Look for an IPv6 socket.
If the netns is a negative signed 32-bit integer, then
the socket lookup table in the netns associated with the
ctx will be used. For the TC hooks, this is the netns of
the device in the skb. For socket hooks, this is the
netns of the socket. If netns is any other signed 32-bit
value greater than or equal to zero then it specifies the
ID of the netns relative to the netns associated with the
ctx. netns values beyond the range of 32-bit integers are
reserved for future use.
All values for flags are reserved for future usage, and
must be left at zero.
This helper is available only if the kernel was compiled
with CONFIG_NET configuration option.
Return Pointer to struct bpf_sock, or NULL in case of failure.
For sockets with reuseport option, the struct bpf_sock
result is from reuse->socks[] using the hash of the tu-
ple.
struct bpf_sock *bpf_sk_lookup_udp(void *ctx, struct bpf_sock_tuple
*tuple, u32 tuple_size, u64 netns, u64 flags)
Description
Look for UDP socket matching tuple, optionally in a child
network namespace netns. The return value must be
checked, and if non-NULL, released via bpf_sk_release().
The ctx should point to the context of the program, such
as the skb or socket (depending on the hook in use). This
is used to determine the base network namespace for the
lookup.
tuple_size must be one of:
sizeof(tuple->ipv4)
Look for an IPv4 socket.
sizeof(tuple->ipv6)
Look for an IPv6 socket.
If the netns is a negative signed 32-bit integer, then
the socket lookup table in the netns associated with the
ctx will be used. For the TC hooks, this is the netns of
the device in the skb. For socket hooks, this is the
netns of the socket. If netns is any other signed 32-bit
value greater than or equal to zero then it specifies the
ID of the netns relative to the netns associated with the
ctx. netns values beyond the range of 32-bit integers are
reserved for future use.
All values for flags are reserved for future usage, and
must be left at zero.
This helper is available only if the kernel was compiled
with CONFIG_NET configuration option.
Return Pointer to struct bpf_sock, or NULL in case of failure.
For sockets with reuseport option, the struct bpf_sock
result is from reuse->socks[] using the hash of the tu-
ple.
long bpf_sk_release(void *sock)
Description
Release the reference held by sock. sock must be a
non-NULL pointer that was returned from
bpf_sk_lookup_xxx().
Return 0 on success, or a negative error in case of failure.
long bpf_map_push_elem(struct bpf_map *map, const void *value, u64
flags)
Description
Push an element value in map. flags is one of:
BPF_EXIST
If the queue/stack is full, the oldest element is
removed to make room for this.
Return 0 on success, or a negative error in case of failure.
long bpf_map_pop_elem(struct bpf_map *map, void *value)
Description
Pop an element from map.
Return 0 on success, or a negative error in case of failure.
long bpf_map_peek_elem(struct bpf_map *map, void *value)
Description
Get an element from map without removing it.
Return 0 on success, or a negative error in case of failure.
long bpf_msg_push_data(struct sk_msg_buff *msg, u32 start, u32 len, u64
flags)
Description
For socket policies, insert len bytes into msg at offset
start.
If a program of type BPF_PROG_TYPE_SK_MSG is run on a msg
it may want to insert metadata or options into the msg.
This can later be read and used by any of the lower layer
BPF hooks.
This helper may fail if under memory pressure (a malloc
fails) in these cases BPF programs will get an appropri-
ate error and BPF programs will need to handle them.
Return 0 on success, or a negative error in case of failure.
long bpf_msg_pop_data(struct sk_msg_buff *msg, u32 start, u32 len, u64
flags)
Description
Will remove len bytes from a msg starting at byte start.
This may result in ENOMEM errors under certain situations
if an allocation and copy are required due to a full ring
buffer. However, the helper will try to avoid doing the
allocation if possible. Other errors can occur if input
parameters are invalid either due to start byte not being
valid part of msg payload and/or pop value being to
large.
Return 0 on success, or a negative error in case of failure.
long bpf_rc_pointer_rel(void *ctx, s32 rel_x, s32 rel_y)
Description
This helper is used in programs implementing IR decoding,
to report a successfully decoded pointer movement.
The ctx should point to the lirc sample as passed into
the program.
This helper is only available is the kernel was compiled
with the CONFIG_BPF_LIRC_MODE2 configuration option set
to "y".
Return 0
long bpf_spin_lock(struct bpf_spin_lock *lock)
Description
Acquire a spinlock represented by the pointer lock, which
is stored as part of a value of a map. Taking the lock
allows to safely update the rest of the fields in that
value. The spinlock can (and must) later be released with
a call to bpf_spin_unlock(lock).
Spinlocks in BPF programs come with a number of restric-
tions and constraints:
• bpf_spin_lock objects are only allowed inside maps of
types BPF_MAP_TYPE_HASH and BPF_MAP_TYPE_ARRAY (this
list could be extended in the future).
• BTF description of the map is mandatory.
• The BPF program can take ONE lock at a time, since tak-
ing two or more could cause dead locks.
• Only one struct bpf_spin_lock is allowed per map ele-
ment.
• When the lock is taken, calls (either BPF to BPF or
helpers) are not allowed.
• The BPF_LD_ABS and BPF_LD_IND instructions are not al-
lowed inside a spinlock-ed region.
• The BPF program MUST call bpf_spin_unlock() to release
the lock, on all execution paths, before it returns.
• The BPF program can access struct bpf_spin_lock only
via the bpf_spin_lock() and bpf_spin_unlock() helpers.
Loading or storing data into the struct bpf_spin_lock
lock; field of a map is not allowed.
• To use the bpf_spin_lock() helper, the BTF description
of the map value must be a struct and have struct
bpf_spin_lock anyname; field at the top level. Nested
lock inside another struct is not allowed.
• The struct bpf_spin_lock lock field in a map value must
be aligned on a multiple of 4 bytes in that value.
• Syscall with command BPF_MAP_LOOKUP_ELEM does not copy
the bpf_spin_lock field to user space.
• Syscall with command BPF_MAP_UPDATE_ELEM, or update
from a BPF program, do not update the bpf_spin_lock
field.
• bpf_spin_lock cannot be on the stack or inside a net-
working packet (it can only be inside of a map values).
• bpf_spin_lock is available to root only.
• Tracing programs and socket filter programs cannot use
bpf_spin_lock() due to insufficient preemption checks
(but this may change in the future).
• bpf_spin_lock is not allowed in inner maps of
map-in-map.
Return 0
long bpf_spin_unlock(struct bpf_spin_lock *lock)
Description
Release the lock previously locked by a call to
bpf_spin_lock(lock).
Return 0
struct bpf_sock *bpf_sk_fullsock(struct bpf_sock *sk)
Description
This helper gets a struct bpf_sock pointer such that all
the fields in this bpf_sock can be accessed.
Return A struct bpf_sock pointer on success, or NULL in case of
failure.
struct bpf_tcp_sock *bpf_tcp_sock(struct bpf_sock *sk)
Description
This helper gets a struct bpf_tcp_sock pointer from a
struct bpf_sock pointer.
Return A struct bpf_tcp_sock pointer on success, or NULL in case
of failure.
long bpf_skb_ecn_set_ce(struct sk_buff *skb)
Description
Set ECN (Explicit Congestion Notification) field of IP
header to CE (Congestion Encountered) if current value is
ECT (ECN Capable Transport). Otherwise, do nothing. Works
with IPv6 and IPv4.
Return 1 if the CE flag is set (either by the current helper
call or because it was already present), 0 if it is not
set.
struct bpf_sock *bpf_get_listener_sock(struct bpf_sock *sk)
Description
Return a struct bpf_sock pointer in TCP_LISTEN state.
bpf_sk_release() is unnecessary and not allowed.
Return A struct bpf_sock pointer on success, or NULL in case of
failure.
struct bpf_sock *bpf_skc_lookup_tcp(void *ctx, struct bpf_sock_tuple
*tuple, u32 tuple_size, u64 netns, u64 flags)
Description
Look for TCP socket matching tuple, optionally in a child
network namespace netns. The return value must be
checked, and if non-NULL, released via bpf_sk_release().
This function is identical to bpf_sk_lookup_tcp(), except
that it also returns timewait or request sockets. Use
bpf_sk_fullsock() or bpf_tcp_sock() to access the full
structure.
This helper is available only if the kernel was compiled
with CONFIG_NET configuration option.
Return Pointer to struct bpf_sock, or NULL in case of failure.
For sockets with reuseport option, the struct bpf_sock
result is from reuse->socks[] using the hash of the tu-
ple.
long bpf_tcp_check_syncookie(void *sk, void *iph, u32 iph_len, struct
tcphdr *th, u32 th_len)
Description
Check whether iph and th contain a valid SYN cookie ACK
for the listening socket in sk.
iph points to the start of the IPv4 or IPv6 header, while
iph_len contains sizeof(struct iphdr) or sizeof(struct
ipv6hdr).
th points to the start of the TCP header, while th_len
contains the length of the TCP header (at least
sizeof(struct tcphdr)).
Return 0 if iph and th are a valid SYN cookie ACK, or a negative
error otherwise.
long bpf_sysctl_get_name(struct bpf_sysctl *ctx, char *buf, size_t
buf_len, u64 flags)
Description
Get name of sysctl in /proc/sys/ and copy it into pro-
vided by program buffer buf of size buf_len.
The buffer is always NUL terminated, unless it's
zero-sized.
If flags is zero, full name (e.g. "net/ipv4/tcp_mem") is
copied. Use BPF_F_SYSCTL_BASE_NAME flag to copy base name
only (e.g. "tcp_mem").
Return Number of character copied (not including the trailing
NUL).
-E2BIG if the buffer wasn't big enough (buf will contain
truncated name in this case).
long bpf_sysctl_get_current_value(struct bpf_sysctl *ctx, char *buf,
size_t buf_len)
Description
Get current value of sysctl as it is presented in
/proc/sys (incl. newline, etc), and copy it as a string
into provided by program buffer buf of size buf_len.
The whole value is copied, no matter what file position
user space issued e.g. sys_read at.
The buffer is always NUL terminated, unless it's
zero-sized.
Return Number of character copied (not including the trailing
NUL).
-E2BIG if the buffer wasn't big enough (buf will contain
truncated name in this case).
-EINVAL if current value was unavailable, e.g. because
sysctl is uninitialized and read returns -EIO for it.
long bpf_sysctl_get_new_value(struct bpf_sysctl *ctx, char *buf, size_t
buf_len)
Description
Get new value being written by user space to sysctl (be-
fore the actual write happens) and copy it as a string
into provided by program buffer buf of size buf_len.
User space may write new value at file position > 0.
The buffer is always NUL terminated, unless it's
zero-sized.
Return Number of character copied (not including the trailing
NUL).
-E2BIG if the buffer wasn't big enough (buf will contain
truncated name in this case).
-EINVAL if sysctl is being read.
long bpf_sysctl_set_new_value(struct bpf_sysctl *ctx, const char *buf,
size_t buf_len)
Description
Override new value being written by user space to sysctl
with value provided by program in buffer buf of size
buf_len.
buf should contain a string in same form as provided by
user space on sysctl write.
User space may write new value at file position > 0. To
override the whole sysctl value file position should be
set to zero.
Return 0 on success.
-E2BIG if the buf_len is too big.
-EINVAL if sysctl is being read.
long bpf_strtol(const char *buf, size_t buf_len, u64 flags, long *res)
Description
Convert the initial part of the string from buffer buf of
size buf_len to a long integer according to the given
base and save the result in res.
The string may begin with an arbitrary amount of white
space (as determined by isspace(3)) followed by a single
optional '-' sign.
Five least significant bits of flags encode base, other
bits are currently unused.
Base must be either 8, 10, 16 or 0 to detect it automati-
cally similar to user space strtol(3).
Return Number of characters consumed on success. Must be posi-
tive but no more than buf_len.
-EINVAL if no valid digits were found or unsupported base
was provided.
-ERANGE if resulting value was out of range.
long bpf_strtoul(const char *buf, size_t buf_len, u64 flags, unsigned
long *res)
Description
Convert the initial part of the string from buffer buf of
size buf_len to an unsigned long integer according to the
given base and save the result in res.
The string may begin with an arbitrary amount of white
space (as determined by isspace(3)).
Five least significant bits of flags encode base, other
bits are currently unused.
Base must be either 8, 10, 16 or 0 to detect it automati-
cally similar to user space strtoul(3).
Return Number of characters consumed on success. Must be posi-
tive but no more than buf_len.
-EINVAL if no valid digits were found or unsupported base
was provided.
-ERANGE if resulting value was out of range.
void *bpf_sk_storage_get(struct bpf_map *map, void *sk, void *value,
u64 flags)
Description
Get a bpf-local-storage from a sk.
Logically, it could be thought of getting the value from
a map with sk as the key. From this perspective, the
usage is not much different from bpf_map_lookup_elem(map,
&sk) except this helper enforces the key must be a full
socket and the map must be a BPF_MAP_TYPE_SK_STORAGE
also.
Underneath, the value is stored locally at sk instead of
the map. The map is used as the bpf-local-storage
"type". The bpf-local-storage "type" (i.e. the map) is
searched against all bpf-local-storages residing at sk.
sk is a kernel struct sock pointer for LSM program. sk
is a struct bpf_sock pointer for other program types.
An optional flags (BPF_SK_STORAGE_GET_F_CREATE) can be
used such that a new bpf-local-storage will be created if
one does not exist. value can be used together with
BPF_SK_STORAGE_GET_F_CREATE to specify the initial value
of a bpf-local-storage. If value is NULL, the new
bpf-local-storage will be zero initialized.
Return A bpf-local-storage pointer is returned on success.
NULL if not found or there was an error in adding a new
bpf-local-storage.
long bpf_sk_storage_delete(struct bpf_map *map, void *sk)
Description
Delete a bpf-local-storage from a sk.
Return 0 on success.
-ENOENT if the bpf-local-storage cannot be found. -EIN-
VAL if sk is not a fullsock (e.g. a request_sock).
long bpf_send_signal(u32 sig)
Description
Send signal sig to the process of the current task. The
signal may be delivered to any of this process's threads.
Return 0 on success or successfully queued.
-EBUSY if work queue under nmi is full.
-EINVAL if sig is invalid.
-EPERM if no permission to send the sig.
-EAGAIN if bpf program can try again.
s64 bpf_tcp_gen_syncookie(void *sk, void *iph, u32 iph_len, struct
tcphdr *th, u32 th_len)
Description
Try to issue a SYN cookie for the packet with correspond-
ing IP/TCP headers, iph and th, on the listening socket
in sk.
iph points to the start of the IPv4 or IPv6 header, while
iph_len contains sizeof(struct iphdr) or sizeof(struct
ipv6hdr).
th points to the start of the TCP header, while th_len
contains the length of the TCP header with options (at
least sizeof(struct tcphdr)).
Return On success, lower 32 bits hold the generated SYN cookie
in followed by 16 bits which hold the MSS value for that
cookie, and the top 16 bits are unused.
On failure, the returned value is one of the following:
-EINVAL SYN cookie cannot be issued due to error
-ENOENT SYN cookie should not be issued (no SYN flood)
-EOPNOTSUPP kernel configuration does not enable SYN
cookies
-EPROTONOSUPPORT IP packet version is not 4 or 6
long bpf_skb_output(void *ctx, struct bpf_map *map, u64 flags, void
*data, u64 size)
Description
Write raw data blob into a special BPF perf event held by
map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY. This perf
event must have the following attributes: PERF_SAMPLE_RAW
as sample_type, PERF_TYPE_SOFTWARE as type, and
PERF_COUNT_SW_BPF_OUTPUT as config.
The flags are used to indicate the index in map for which
the value must be put, masked with BPF_F_INDEX_MASK. Al-
ternatively, flags can be set to BPF_F_CURRENT_CPU to in-
dicate that the index of the current CPU core should be
used.
The value to write, of size, is passed through eBPF stack
and pointed by data.
ctx is a pointer to in-kernel struct sk_buff.
This helper is similar to bpf_perf_event_output() but re-
stricted to raw_tracepoint bpf programs.
Return 0 on success, or a negative error in case of failure.
long bpf_probe_read_user(void *dst, u32 size, const void *unsafe_ptr)
Description
Safely attempt to read size bytes from user space address
unsafe_ptr and store the data in dst.
Return 0 on success, or a negative error in case of failure.
long bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)
Description
Safely attempt to read size bytes from kernel space ad-
dress unsafe_ptr and store the data in dst.
Return 0 on success, or a negative error in case of failure.
long bpf_probe_read_user_str(void *dst, u32 size, const void *un-
safe_ptr)
Description
Copy a NUL terminated string from an unsafe user address
unsafe_ptr to dst. The size should include the terminat-
ing NUL byte. In case the string length is smaller than
size, the target is not padded with further NUL bytes. If
the string length is larger than size, just size-1 bytes
are copied and the last byte is set to NUL.
On success, returns the number of bytes that were writ-
ten, including the terminal NUL. This makes this helper
useful in tracing programs for reading strings, and more
importantly to get its length at runtime. See the follow-
ing snippet:
SEC("kprobe/sys_open")
void bpf_sys_open(struct pt_regs *ctx)
{
char buf[PATHLEN]; // PATHLEN is defined to 256
int res = bpf_probe_read_user_str(buf, sizeof(buf),
ctx->di);
// Consume buf, for example push it to
// userspace via bpf_perf_event_output(); we
// can use res (the string length) as event
// size, after checking its boundaries.
}
In comparison, using bpf_probe_read_user() helper here
instead to read the string would require to estimate the
length at compile time, and would often result in copying
more memory than necessary.
Another useful use case is when parsing individual
process arguments or individual environment variables
navigating current->mm->arg_start and cur-
rent->mm->env_start: using this helper and the return
value, one can quickly iterate at the right offset of the
memory area.
Return On success, the strictly positive length of the output
string, including the trailing NUL character. On error, a
negative value.
long bpf_probe_read_kernel_str(void *dst, u32 size, const void *un-
safe_ptr)
Description
Copy a NUL terminated string from an unsafe kernel ad-
dress unsafe_ptr to dst. Same semantics as with
bpf_probe_read_user_str() apply.
Return On success, the strictly positive length of the string,
including the trailing NUL character. On error, a nega-
tive value.
long bpf_tcp_send_ack(void *tp, u32 rcv_nxt)
Description
Send out a tcp-ack. tp is the in-kernel struct tcp_sock.
rcv_nxt is the ack_seq to be sent out.
Return 0 on success, or a negative error in case of failure.
long bpf_send_signal_thread(u32 sig)
Description
Send signal sig to the thread corresponding to the cur-
rent task.
Return 0 on success or successfully queued.
-EBUSY if work queue under nmi is full.
-EINVAL if sig is invalid.
-EPERM if no permission to send the sig.
-EAGAIN if bpf program can try again.
u64 bpf_jiffies64(void)
Description
Obtain the 64bit jiffies
Return The 64 bit jiffies
long bpf_read_branch_records(struct bpf_perf_event_data *ctx, void
*buf, u32 size, u64 flags)
Description
For an eBPF program attached to a perf event, retrieve
the branch records (struct perf_branch_entry) associated
to ctx and store it in the buffer pointed by buf up to
size size bytes.
Return On success, number of bytes written to buf. On error, a
negative value.
The flags can be set to BPF_F_GET_BRANCH_RECORDS_SIZE to
instead return the number of bytes required to store all
the branch entries. If this flag is set, buf may be NULL.
-EINVAL if arguments invalid or size not a multiple of
sizeof(struct perf_branch_entry).
-ENOENT if architecture does not support branch records.
long bpf_get_ns_current_pid_tgid(u64 dev, u64 ino, struct
bpf_pidns_info *nsdata, u32 size)
Description
Returns 0 on success, values for pid and tgid as seen
from the current namespace will be returned in nsdata.
Return 0 on success, or one of the following in case of failure:
-EINVAL if dev and inum supplied don't match dev_t and
inode number with nsfs of current task, or if dev conver-
sion to dev_t lost high bits.
-ENOENT if pidns does not exists for the current task.
long bpf_xdp_output(void *ctx, struct bpf_map *map, u64 flags, void
*data, u64 size)
Description
Write raw data blob into a special BPF perf event held by
map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY. This perf
event must have the following attributes: PERF_SAMPLE_RAW
as sample_type, PERF_TYPE_SOFTWARE as type, and
PERF_COUNT_SW_BPF_OUTPUT as config.
The flags are used to indicate the index in map for which
the value must be put, masked with BPF_F_INDEX_MASK. Al-
ternatively, flags can be set to BPF_F_CURRENT_CPU to in-
dicate that the index of the current CPU core should be
used.
The value to write, of size, is passed through eBPF stack
and pointed by data.
ctx is a pointer to in-kernel struct xdp_buff.
This helper is similar to bpf_perf_eventoutput() but re-
stricted to raw_tracepoint bpf programs.
Return 0 on success, or a negative error in case of failure.
u64 bpf_get_netns_cookie(void *ctx)
Description
Retrieve the cookie (generated by the kernel) of the net-
work namespace the input ctx is associated with. The net-
work namespace cookie remains stable for its lifetime and
provides a global identifier that can be assumed unique.
If ctx is NULL, then the helper returns the cookie for
the initial network namespace. The cookie itself is very
similar to that of bpf_get_socket_cookie() helper, but
for network namespaces instead of sockets.
Return A 8-byte long opaque number.
u64 bpf_get_current_ancestor_cgroup_id(int ancestor_level)
Description
Return id of cgroup v2 that is ancestor of the cgroup as-
sociated with the current task at the ancestor_level. The
root cgroup is at ancestor_level zero and each step down
the hierarchy increments the level. If ancestor_level ==
level of cgroup associated with the current task, then
return value will be the same as that of bpf_get_cur-
rent_cgroup_id().
The helper is useful to implement policies based on
cgroups that are upper in hierarchy than immediate cgroup
associated with the current task.
The format of returned id and helper limitations are same
as in bpf_get_current_cgroup_id().
Return The id is returned or 0 in case the id could not be re-
trieved.
long bpf_sk_assign(struct sk_buff *skb, void *sk, u64 flags)
Description
Helper is overloaded depending on BPF program type. This
description applies to BPF_PROG_TYPE_SCHED_CLS and
BPF_PROG_TYPE_SCHED_ACT programs.
Assign the sk to the skb. When combined with appropriate
routing configuration to receive the packet towards the
socket, will cause skb to be delivered to the specified
socket. Subsequent redirection of skb via bpf_redi-
rect(), bpf_clone_redirect() or other methods outside of
BPF may interfere with successful delivery to the socket.
This operation is only valid from TC ingress path.
The flags argument must be zero.
Return 0 on success, or a negative error in case of failure:
-EINVAL if specified flags are not supported.
-ENOENT if the socket is unavailable for assignment.
-ENETUNREACH if the socket is unreachable (wrong netns).
-EOPNOTSUPP if the operation is not supported, for exam-
ple a call from outside of TC ingress.
long bpf_sk_assign(struct bpf_sk_lookup *ctx, struct bpf_sock *sk, u64
flags)
Description
Helper is overloaded depending on BPF program type. This
description applies to BPF_PROG_TYPE_SK_LOOKUP programs.
Select the sk as a result of a socket lookup.
For the operation to succeed passed socket must be com-
patible with the packet description provided by the ctx
object.
L4 protocol (IPPROTO_TCP or IPPROTO_UDP) must be an exact
match. While IP family (AF_INET or AF_INET6) must be com-
patible, that is IPv6 sockets that are not v6-only can be
selected for IPv4 packets.
Only TCP listeners and UDP unconnected sockets can be se-
lected. sk can also be NULL to reset any previous selec-
tion.
flags argument can combination of following values:
• BPF_SK_LOOKUP_F_REPLACE to override the previous socket
selection, potentially done by a BPF program that ran
before us.
• BPF_SK_LOOKUP_F_NO_REUSEPORT to skip load-balancing
within reuseport group for the socket being selected.
On success ctx->sk will point to the selected socket.
Return 0 on success, or a negative errno in case of failure.
• -EAFNOSUPPORT if socket family (sk->family) is not com-
patible with packet family (ctx->family).
• -EEXIST if socket has been already selected, poten-
tially by another program, and BPF_SK_LOOKUP_F_REPLACE
flag was not specified.
• -EINVAL if unsupported flags were specified.
• -EPROTOTYPE if socket L4 protocol (sk->protocol)
doesn't match packet protocol (ctx->protocol).
• -ESOCKTNOSUPPORT if socket is not in allowed state (TCP
listening or UDP unconnected).
u64 bpf_ktime_get_boot_ns(void)
Description
Return the time elapsed since system boot, in nanosec-
onds. Does include the time the system was suspended.
See: clock_gettime(CLOCK_BOOTTIME)
Return Current ktime.
long bpf_seq_printf(struct seq_file *m, const char *fmt, u32 fmt_size,
const void *data, u32 data_len)
Description
bpf_seq_printf() uses seq_file seq_printf() to print out
the format string. The m represents the seq_file. The
fmt and fmt_size are for the format string itself. The
data and data_len are format string arguments. The data
are a u64 array and corresponding format string values
are stored in the array. For strings and pointers where
pointees are accessed, only the pointer values are stored
in the data array. The data_len is the size of data in
bytes - must be a multiple of 8.
Formats %s, %p{i,I}{4,6} requires to read kernel memory.
Reading kernel memory may fail due to either invalid ad-
dress or valid address but requiring a major memory
fault. If reading kernel memory fails, the string for %s
will be an empty string, and the ip address for
%p{i,I}{4,6} will be 0. Not returning error to bpf pro-
gram is consistent with what bpf_trace_printk() does for
now.
Return 0 on success, or a negative error in case of failure:
-EBUSY if per-CPU memory copy buffer is busy, can try
again by returning 1 from bpf program.
-EINVAL if arguments are invalid, or if fmt is in-
valid/unsupported.
-E2BIG if fmt contains too many format specifiers.
-EOVERFLOW if an overflow happened: The same object will
be tried again.
long bpf_seq_write(struct seq_file *m, const void *data, u32 len)
Description
bpf_seq_write() uses seq_file seq_write() to write the
data. The m represents the seq_file. The data and len
represent the data to write in bytes.
Return 0 on success, or a negative error in case of failure:
-EOVERFLOW if an overflow happened: The same object will
be tried again.
u64 bpf_sk_cgroup_id(void *sk)
Description
Return the cgroup v2 id of the socket sk.
sk must be a non-NULL pointer to a socket, e.g. one re-
turned from bpf_sk_lookup_xxx(), bpf_sk_fullsock(), etc.
The format of returned id is same as in
bpf_skb_cgroup_id().
This helper is available only if the kernel was compiled
with the CONFIG_SOCK_CGROUP_DATA configuration option.
Return The id is returned or 0 in case the id could not be re-
trieved.
u64 bpf_sk_ancestor_cgroup_id(void *sk, int ancestor_level)
Description
Return id of cgroup v2 that is ancestor of cgroup associ-
ated with the sk at the ancestor_level. The root cgroup
is at ancestor_level zero and each step down the hierar-
chy increments the level. If ancestor_level == level of
cgroup associated with sk, then return value will be same
as that of bpf_sk_cgroup_id().
The helper is useful to implement policies based on
cgroups that are upper in hierarchy than immediate cgroup
associated with sk.
The format of returned id and helper limitations are same
as in bpf_sk_cgroup_id().
Return The id is returned or 0 in case the id could not be re-
trieved.
long bpf_ringbuf_output(void *ringbuf, void *data, u64 size, u64 flags)
Description
Copy size bytes from data into a ring buffer ringbuf. If
BPF_RB_NO_WAKEUP is specified in flags, no notification
of new data availability is sent. If BPF_RB_FORCE_WAKEUP
is specified in flags, notification of new data avail-
ability is sent unconditionally. If 0 is specified in
flags, an adaptive notification of new data availability
is sent.
An adaptive notification is a notification sent whenever
the user-space process has caught up and consumed all
available payloads. In case the user-space process is
still processing a previous payload, then no notification
is needed as it will process the newly added payload au-
tomatically.
Return 0 on success, or a negative error in case of failure.
void *bpf_ringbuf_reserve(void *ringbuf, u64 size, u64 flags)
Description
Reserve size bytes of payload in a ring buffer ringbuf.
flags must be 0.
Return Valid pointer with size bytes of memory available; NULL,
otherwise.
void bpf_ringbuf_submit(void *data, u64 flags)
Description
Submit reserved ring buffer sample, pointed to by data.
If BPF_RB_NO_WAKEUP is specified in flags, no notifica-
tion of new data availability is sent. If
BPF_RB_FORCE_WAKEUP is specified in flags, notification
of new data availability is sent unconditionally. If 0
is specified in flags, an adaptive notification of new
data availability is sent.
See 'bpf_ringbuf_output()' for the definition of adaptive
notification.
Return Nothing. Always succeeds.
void bpf_ringbuf_discard(void *data, u64 flags)
Description
Discard reserved ring buffer sample, pointed to by data.
If BPF_RB_NO_WAKEUP is specified in flags, no notifica-
tion of new data availability is sent. If
BPF_RB_FORCE_WAKEUP is specified in flags, notification
of new data availability is sent unconditionally. If 0
is specified in flags, an adaptive notification of new
data availability is sent.
See 'bpf_ringbuf_output()' for the definition of adaptive
notification.
Return Nothing. Always succeeds.
u64 bpf_ringbuf_query(void *ringbuf, u64 flags)
Description
Query various characteristics of provided ring buffer.
What exactly is queries is determined by flags:
• BPF_RB_AVAIL_DATA: Amount of data not yet consumed.
• BPF_RB_RING_SIZE: The size of ring buffer.
• BPF_RB_CONS_POS: Consumer position (can wrap around).
• BPF_RB_PROD_POS: Producer(s) position (can wrap
around).
Data returned is just a momentary snapshot of actual val-
ues and could be inaccurate, so this facility should be
used to power heuristics and for reporting, not to make
100% correct calculation.
Return Requested value, or 0, if flags are not recognized.
long bpf_csum_level(struct sk_buff *skb, u64 level)
Description
Change the skbs checksum level by one layer up or down,
or reset it entirely to none in order to have the stack
perform checksum validation. The level is applicable to
the following protocols: TCP, UDP, GRE, SCTP, FCOE. For
example, a decap of | ETH | IP | UDP | GUE | IP | TCP |
into | ETH | IP | TCP | through bpf_skb_adjust_room()
helper with passing in BPF_F_ADJ_ROOM_NO_CSUM_RESET flag
would require one call to bpf_csum_level() with
BPF_CSUM_LEVEL_DEC since the UDP header is removed. Simi-
larly, an encap of the latter into the former could be
accompanied by a helper call to bpf_csum_level() with
BPF_CSUM_LEVEL_INC if the skb is still intended to be
processed in higher layers of the stack instead of just
egressing at tc.
There are three supported level settings at this time:
• BPF_CSUM_LEVEL_INC: Increases skb->csum_level for skbs
with CHECKSUM_UNNECESSARY.
• BPF_CSUM_LEVEL_DEC: Decreases skb->csum_level for skbs
with CHECKSUM_UNNECESSARY.
• BPF_CSUM_LEVEL_RESET: Resets skb->csum_level to 0 and
sets CHECKSUM_NONE to force checksum validation by the
stack.
• BPF_CSUM_LEVEL_QUERY: No-op, returns the current
skb->csum_level.
Return 0 on success, or a negative error in case of failure. In
the case of BPF_CSUM_LEVEL_QUERY, the current
skb->csum_level is returned or the error code -EACCES in
case the skb is not subject to CHECKSUM_UNNECESSARY.
struct tcp6_sock *bpf_skc_to_tcp6_sock(void *sk)
Description
Dynamically cast a sk pointer to a tcp6_sock pointer.
Return sk if casting is valid, or NULL otherwise.
struct tcp_sock *bpf_skc_to_tcp_sock(void *sk)
Description
Dynamically cast a sk pointer to a tcp_sock pointer.
Return sk if casting is valid, or NULL otherwise.
struct tcp_timewait_sock *bpf_skc_to_tcp_timewait_sock(void *sk)
Description
Dynamically cast a sk pointer to a tcp_timewait_sock
pointer.
Return sk if casting is valid, or NULL otherwise.
struct tcp_request_sock *bpf_skc_to_tcp_request_sock(void *sk)
Description
Dynamically cast a sk pointer to a tcp_request_sock
pointer.
Return sk if casting is valid, or NULL otherwise.
struct udp6_sock *bpf_skc_to_udp6_sock(void *sk)
Description
Dynamically cast a sk pointer to a udp6_sock pointer.
Return sk if casting is valid, or NULL otherwise.
long bpf_get_task_stack(struct task_struct *task, void *buf, u32 size,
u64 flags)
Description
Return a user or a kernel stack in bpf program provided
buffer. Note: the user stack will only be populated if
the task is the current task; all other tasks will return
-EOPNOTSUPP. To achieve this, the helper needs task,
which is a valid pointer to struct task_struct. To store
the stacktrace, the bpf program provides buf with a non-
negative size.
The last argument, flags, holds the number of stack
frames to skip (from 0 to 255), masked with
BPF_F_SKIP_FIELD_MASK. The next bits can be used to set
the following flags:
BPF_F_USER_STACK
Collect a user space stack instead of a kernel
stack. The task must be the current task.
BPF_F_USER_BUILD_ID
Collect buildid+offset instead of ips for user
stack, only valid if BPF_F_USER_STACK is also
specified.
bpf_get_task_stack() can collect up to
PERF_MAX_STACK_DEPTH both kernel and user frames, subject
to sufficient large buffer size. Note that this limit can
be controlled with the sysctl program, and that it should
be manually increased in order to profile long user
stacks (such as stacks for Java programs). To do so, use:
# sysctl kernel.perf_event_max_stack=<new value>
Return The non-negative copied buf length equal to or less than
size on success, or a negative error in case of failure.
long bpf_load_hdr_opt(struct bpf_sock_ops *skops, void *searchby_res,
u32 len, u64 flags)
Description
Load header option. Support reading a particular TCP
header option for bpf program (BPF_PROG_TYPE_SOCK_OPS).
If flags is 0, it will search the option from the
skops->skb_data. The comment in struct bpf_sock_ops has
details on what skb_data contains under different
skops->op.
The first byte of the searchby_res specifies the kind
that it wants to search.
If the searching kind is an experimental kind (i.e. 253
or 254 according to RFC6994). It also needs to specify
the "magic" which is either 2 bytes or 4 bytes. It then
also needs to specify the size of the magic by using the
2nd byte which is "kind-length" of a TCP header option
and the "kind-length" also includes the first 2 bytes
"kind" and "kind-length" itself as a normal TCP header
option also does.
For example, to search experimental kind 254 with 2 byte
magic 0xeB9F, the searchby_res should be [ 254, 4, 0xeB,
0x9F, 0, 0, .... 0 ].
To search for the standard window scale option (3), the
searchby_res should be [ 3, 0, 0, .... 0 ]. Note,
kind-length must be 0 for regular option.
Searching for No-Op (0) and End-of-Option-List (1) are
not supported.
len must be at least 2 bytes which is the minimal size of
a header option.
Supported flags:
• BPF_LOAD_HDR_OPT_TCP_SYN to search from the saved_syn
packet or the just-received syn packet.
Return > 0 when found, the header option is copied to
searchby_res. The return value is the total length
copied. On failure, a negative error code is returned:
-EINVAL if a parameter is invalid.
-ENOMSG if the option is not found.
-ENOENT if no syn packet is available when
BPF_LOAD_HDR_OPT_TCP_SYN is used.
-ENOSPC if there is not enough space. Only len number of
bytes are copied.
-EFAULT on failure to parse the header options in the
packet.
-EPERM if the helper cannot be used under the current
skops->op.
long bpf_store_hdr_opt(struct bpf_sock_ops *skops, const void *from,
u32 len, u64 flags)
Description
Store header option. The data will be copied from buffer
from with length len to the TCP header.
The buffer from should have the whole option that in-
cludes the kind, kind-length, and the actual option data.
The len must be at least kind-length long. The
kind-length does not have to be 4 byte aligned. The ker-
nel will take care of the padding and setting the 4 bytes
aligned value to th->doff.
This helper will check for duplicated option by searching
the same option in the outgoing skb.
This helper can only be called during
BPF_SOCK_OPS_WRITE_HDR_OPT_CB.
Return 0 on success, or negative error in case of failure:
-EINVAL If param is invalid.
-ENOSPC if there is not enough space in the header.
Nothing has been written
-EEXIST if the option already exists.
-EFAULT on failure to parse the existing header options.
-EPERM if the helper cannot be used under the current
skops->op.
long bpf_reserve_hdr_opt(struct bpf_sock_ops *skops, u32 len, u64
flags)
Description
Reserve len bytes for the bpf header option. The space
will be used by bpf_store_hdr_opt() later in
BPF_SOCK_OPS_WRITE_HDR_OPT_CB.
If bpf_reserve_hdr_opt() is called multiple times, the
total number of bytes will be reserved.
This helper can only be called during
BPF_SOCK_OPS_HDR_OPT_LEN_CB.
Return 0 on success, or negative error in case of failure:
-EINVAL if a parameter is invalid.
-ENOSPC if there is not enough space in the header.
-EPERM if the helper cannot be used under the current
skops->op.
void *bpf_inode_storage_get(struct bpf_map *map, void *inode, void
*value, u64 flags)
Description
Get a bpf_local_storage from an inode.
Logically, it could be thought of as getting the value
from a map with inode as the key. From this perspective,
the usage is not much different from
bpf_map_lookup_elem(map, &inode) except this helper en-
forces the key must be an inode and the map must also be
a BPF_MAP_TYPE_INODE_STORAGE.
Underneath, the value is stored locally at inode instead
of the map. The map is used as the bpf-local-storage
"type". The bpf-local-storage "type" (i.e. the map) is
searched against all bpf_local_storage residing at inode.
An optional flags (BPF_LOCAL_STORAGE_GET_F_CREATE) can be
used such that a new bpf_local_storage will be created if
one does not exist. value can be used together with
BPF_LOCAL_STORAGE_GET_F_CREATE to specify the initial
value of a bpf_local_storage. If value is NULL, the new
bpf_local_storage will be zero initialized.
Return A bpf_local_storage pointer is returned on success.
NULL if not found or there was an error in adding a new
bpf_local_storage.
int bpf_inode_storage_delete(struct bpf_map *map, void *inode)
Description
Delete a bpf_local_storage from an inode.
Return 0 on success.
-ENOENT if the bpf_local_storage cannot be found.
long bpf_d_path(struct path *path, char *buf, u32 sz)
Description
Return full path for given struct path object, which
needs to be the kernel BTF path object. The path is re-
turned in the provided buffer buf of size sz and is zero
terminated.
Return On success, the strictly positive length of the string,
including the trailing NUL character. On error, a nega-
tive value.
long bpf_copy_from_user(void *dst, u32 size, const void *user_ptr)
Description
Read size bytes from user space address user_ptr and
store the data in dst. This is a wrapper of
copy_from_user().
Return 0 on success, or a negative error in case of failure.
long bpf_snprintf_btf(char *str, u32 str_size, struct btf_ptr *ptr, u32
btf_ptr_size, u64 flags)
Description
Use BTF to store a string representation of ptr->ptr in
str, using ptr->type_id. This value should specify the
type that ptr->ptr points to. LLVM
__builtin_btf_type_id(type, 1) can be used to look up vm-
linux BTF type ids. Traversing the data structure using
BTF, the type information and values are stored in the
first str_size - 1 bytes of str. Safe copy of the
pointer data is carried out to avoid kernel crashes dur-
ing operation. Smaller types can use string space on the
stack; larger programs can use map data to store the
string representation.
The string can be subsequently shared with userspace via
bpf_perf_event_output() or ring buffer interfaces.
bpf_trace_printk() is to be avoided as it places too
small a limit on string size to be useful.
flags is a combination of
BTF_F_COMPACT
no formatting around type information
BTF_F_NONAME
no struct/union member names/types
BTF_F_PTR_RAW
show raw (unobfuscated) pointer values; equivalent
to printk specifier %px.
BTF_F_ZERO
show zero-valued struct/union members; they are
not displayed by default
Return The number of bytes that were written (or would have been
written if output had to be truncated due to string
size), or a negative error in cases of failure.
long bpf_seq_printf_btf(struct seq_file *m, struct btf_ptr *ptr, u32
ptr_size, u64 flags)
Description
Use BTF to write to seq_write a string representation of
ptr->ptr, using ptr->type_id as per bpf_snprintf_btf().
flags are identical to those used for bpf_snprintf_btf.
Return 0 on success or a negative error in case of failure.
u64 bpf_skb_cgroup_classid(struct sk_buff *skb)
Description
See bpf_get_cgroup_classid() for the main description.
This helper differs from bpf_get_cgroup_classid() in that
the cgroup v1 net_cls class is retrieved only from the
skb's associated socket instead of the current process.
Return The id is returned or 0 in case the id could not be re-
trieved.
long bpf_redirect_neigh(u32 ifindex, struct bpf_redir_neigh *params,
int plen, u64 flags)
Description
Redirect the packet to another net device of index
ifindex and fill in L2 addresses from neighboring subsys-
tem. This helper is somewhat similar to bpf_redirect(),
except that it populates L2 addresses as well, meaning,
internally, the helper relies on the neighbor lookup for
the L2 address of the nexthop.
The helper will perform a FIB lookup based on the skb's
networking header to get the address of the next hop, un-
less this is supplied by the caller in the params argu-
ment. The plen argument indicates the len of params and
should be set to 0 if params is NULL.
The flags argument is reserved and must be 0. The helper
is currently only supported for tc BPF program types, and
enabled for IPv4 and IPv6 protocols.
Return The helper returns TC_ACT_REDIRECT on success or
TC_ACT_SHOT on error.
void *bpf_per_cpu_ptr(const void *percpu_ptr, u32 cpu)
Description
Take a pointer to a percpu ksym, percpu_ptr, and return a
pointer to the percpu kernel variable on cpu. A ksym is
an extern variable decorated with '__ksym'. For ksym,
there is a global var (either static or global) defined
of the same name in the kernel. The ksym is percpu if the
global var is percpu. The returned pointer points to the
global percpu var on cpu.
bpf_per_cpu_ptr() has the same semantic as per_cpu_ptr()
in the kernel, except that bpf_per_cpu_ptr() may return
NULL. This happens if cpu is larger than nr_cpu_ids. The
caller of bpf_per_cpu_ptr() must check the returned
value.
Return A pointer pointing to the kernel percpu variable on cpu,
or NULL, if cpu is invalid.
void *bpf_this_cpu_ptr(const void *percpu_ptr)
Description
Take a pointer to a percpu ksym, percpu_ptr, and return a
pointer to the percpu kernel variable on this cpu. See
the description of 'ksym' in bpf_per_cpu_ptr().
bpf_this_cpu_ptr() has the same semantic as
this_cpu_ptr() in the kernel. Different from
bpf_per_cpu_ptr(), it would never return NULL.
Return A pointer pointing to the kernel percpu variable on this
cpu.
long bpf_redirect_peer(u32 ifindex, u64 flags)
Description
Redirect the packet to another net device of index
ifindex. This helper is somewhat similar to bpf_redi-
rect(), except that the redirection happens to the
ifindex' peer device and the netns switch takes place
from ingress to ingress without going through the CPU's
backlog queue.
The flags argument is reserved and must be 0. The helper
is currently only supported for tc BPF program types at
the ingress hook and for veth device types. The peer de-
vice must reside in a different network namespace.
Return The helper returns TC_ACT_REDIRECT on success or
TC_ACT_SHOT on error.
void *bpf_task_storage_get(struct bpf_map *map, struct task_struct
*task, void *value, u64 flags)
Description
Get a bpf_local_storage from the task.
Logically, it could be thought of as getting the value
from a map with task as the key. From this perspective,
the usage is not much different from
bpf_map_lookup_elem(map, &task) except this helper en-
forces the key must be a task_struct and the map must
also be a BPF_MAP_TYPE_TASK_STORAGE.
Underneath, the value is stored locally at task instead
of the map. The map is used as the bpf-local-storage
"type". The bpf-local-storage "type" (i.e. the map) is
searched against all bpf_local_storage residing at task.
An optional flags (BPF_LOCAL_STORAGE_GET_F_CREATE) can be
used such that a new bpf_local_storage will be created if
one does not exist. value can be used together with
BPF_LOCAL_STORAGE_GET_F_CREATE to specify the initial
value of a bpf_local_storage. If value is NULL, the new
bpf_local_storage will be zero initialized.
Return A bpf_local_storage pointer is returned on success.
NULL if not found or there was an error in adding a new
bpf_local_storage.
long bpf_task_storage_delete(struct bpf_map *map, struct task_struct
*task)
Description
Delete a bpf_local_storage from a task.
Return 0 on success.
-ENOENT if the bpf_local_storage cannot be found.
struct task_struct *bpf_get_current_task_btf(void)
Description
Return a BTF pointer to the "current" task. This pointer
can also be used in helpers that accept an
ARG_PTR_TO_BTF_ID of type task_struct.
Return Pointer to the current task.
long bpf_bprm_opts_set(struct linux_binprm *bprm, u64 flags)
Description
Set or clear certain options on bprm:
BPF_F_BPRM_SECUREEXEC Set the secureexec bit which sets
the AT_SECURE auxv for glibc. The bit is cleared if the
flag is not specified.
Return -EINVAL if invalid flags are passed, zero otherwise.
u64 bpf_ktime_get_coarse_ns(void)
Description
Return a coarse-grained version of the time elapsed since
system boot, in nanoseconds. Does not include time the
system was suspended.
See: clock_gettime(CLOCK_MONOTONIC_COARSE)
Return Current ktime.
long bpf_ima_inode_hash(struct inode *inode, void *dst, u32 size)
Description
Returns the stored IMA hash of the inode (if it's avail-
able). If the hash is larger than size, then only size
bytes will be copied to dst
Return The hash_algo is returned on success, -EOPNOTSUP if IMA
is disabled or -EINVAL if invalid arguments are passed.
struct socket *bpf_sock_from_file(struct file *file)
Description
If the given file represents a socket, returns the asso-
ciated socket.
Return A pointer to a struct socket on success or NULL if the
file is not a socket.
long bpf_check_mtu(void *ctx, u32 ifindex, u32 *mtu_len, s32 len_diff,
u64 flags)
Description
Check packet size against exceeding MTU of net device
(based on ifindex). This helper will likely be used in
combination with helpers that adjust/change the packet
size.
The argument len_diff can be used for querying with a
planned size change. This allows to check MTU prior to
changing packet ctx. Providing a len_diff adjustment that
is larger than the actual packet size (resulting in nega-
tive packet size) will in principle not exceed the MTU,
which is why it is not considered a failure. Other BPF
helpers are needed for performing the planned size
change; therefore the responsibility for catching a nega-
tive packet size belongs in those helpers.
Specifying ifindex zero means the MTU check is performed
against the current net device. This is practical if
this isn't used prior to redirect.
On input mtu_len must be a valid pointer, else verifier
will reject BPF program. If the value mtu_len is ini-
tialized to zero then the ctx packet size is use. When
value mtu_len is provided as input this specify the L3
length that the MTU check is done against. Remember XDP
and TC length operate at L2, but this value is L3 as this
correlate to MTU and IP-header tot_len values which are
L3 (similar behavior as bpf_fib_lookup).
The Linux kernel route table can configure MTUs on a more
specific per route level, which is not provided by this
helper. For route level MTU checks use the
bpf_fib_lookup() helper.
ctx is either struct xdp_md for XDP programs or struct
sk_buff for tc cls_act programs.
The flags argument can be a combination of one or more of
the following values:
BPF_MTU_CHK_SEGS
This flag will only works for ctx struct sk_buff.
If packet context contains extra packet segment
buffers (often knows as GSO skb), then MTU check
is harder to check at this point, because in
transmit path it is possible for the skb packet to
get re-segmented (depending on net device fea-
tures). This could still be a MTU violation, so
this flag enables performing MTU check against
segments, with a different violation return code
to tell it apart. Check cannot use len_diff.
On return mtu_len pointer contains the MTU value of the
net device. Remember the net device configured MTU is
the L3 size, which is returned here and XDP and TC length
operate at L2. Helper take this into account for you,
but remember when using MTU value in your BPF-code.
Return
• 0 on success, and populate MTU value in mtu_len
pointer.
• < 0 if any input argument is invalid (mtu_len not up-
dated)
MTU violations return positive values, but also populate
MTU value in mtu_len pointer, as this can be needed for
implementing PMTU handing:
• BPF_MTU_CHK_RET_FRAG_NEEDED
• BPF_MTU_CHK_RET_SEGS_TOOBIG
long bpf_for_each_map_elem(struct bpf_map *map, void *callback_fn, void
*callback_ctx, u64 flags)
Description
For each element in map, call callback_fn function with
map, callback_ctx and other map-specific parameters. The
callback_fn should be a static function and the call-
back_ctx should be a pointer to the stack. The flags is
used to control certain aspects of the helper. Cur-
rently, the flags must be 0.
The following are a list of supported map types and their
respective expected callback signatures:
BPF_MAP_TYPE_HASH, BPF_MAP_TYPE_PERCPU_HASH,
BPF_MAP_TYPE_LRU_HASH, BPF_MAP_TYPE_LRU_PERCPU_HASH,
BPF_MAP_TYPE_ARRAY, BPF_MAP_TYPE_PERCPU_ARRAY
long (*callback_fn)(struct bpf_map *map, const void *key,
void *value, void *ctx);
For per_cpu maps, the map_value is the value on the cpu
where the bpf_prog is running.
If callback_fn return 0, the helper will continue to the
next element. If return value is 1, the helper will skip
the rest of elements and return. Other return values are
not used now.
Return The number of traversed map elements for success, -EINVAL
for invalid flags.
long bpf_snprintf(char *str, u32 str_size, const char *fmt, u64 *data,
u32 data_len)
Description
Outputs a string into the str buffer of size str_size
based on a format string stored in a read-only map
pointed by fmt.
Each format specifier in fmt corresponds to one u64 ele-
ment in the data array. For strings and pointers where
pointees are accessed, only the pointer values are stored
in the data array. The data_len is the size of data in
bytes - must be a multiple of 8.
Formats %s and %p{i,I}{4,6} require to read kernel mem-
ory. Reading kernel memory may fail due to either invalid
address or valid address but requiring a major memory
fault. If reading kernel memory fails, the string for %s
will be an empty string, and the ip address for
%p{i,I}{4,6} will be 0. Not returning error to bpf pro-
gram is consistent with what bpf_trace_printk() does for
now.
Return The strictly positive length of the formatted string, in-
cluding the trailing zero character. If the return value
is greater than str_size, str contains a truncated
string, guaranteed to be zero-terminated except when
str_size is 0.
Or -EBUSY if the per-CPU memory copy buffer is busy.
long bpf_sys_bpf(u32 cmd, void *attr, u32 attr_size)
Description
Execute bpf syscall with given arguments.
Return A syscall result.
long bpf_btf_find_by_name_kind(char *name, int name_sz, u32 kind, int
flags)
Description
Find BTF type with given name and kind in vmlinux BTF or
in module's BTFs.
Return Returns btf_id and btf_obj_fd in lower and upper 32 bits.
long bpf_sys_close(u32 fd)
Description
Execute close syscall for given FD.
Return A syscall result.
long bpf_timer_init(struct bpf_timer *timer, struct bpf_map *map, u64
flags)
Description
Initialize the timer. First 4 bits of flags specify
clockid. Only CLOCK_MONOTONIC, CLOCK_REALTIME,
CLOCK_BOOTTIME are allowed. All other bits of flags are
reserved. The verifier will reject the program if timer
is not from the same map.
Return 0 on success. -EBUSY if timer is already initialized.
-EINVAL if invalid flags are passed. -EPERM if timer is
in a map that doesn't have any user references. The user
space should either hold a file descriptor to a map with
timers or pin such map in bpffs. When map is unpinned or
file descriptor is closed all timers in the map will be
cancelled and freed.
long bpf_timer_set_callback(struct bpf_timer *timer, void *callback_fn)
Description
Configure the timer to call callback_fn static function.
Return 0 on success. -EINVAL if timer was not initialized with
bpf_timer_init() earlier. -EPERM if timer is in a map
that doesn't have any user references. The user space
should either hold a file descriptor to a map with timers
or pin such map in bpffs. When map is unpinned or file
descriptor is closed all timers in the map will be can-
celled and freed.
long bpf_timer_start(struct bpf_timer *timer, u64 nsecs, u64 flags)
Description
Set timer expiration N nanoseconds from the current time.
The configured callback will be invoked in soft irq con-
text on some cpu and will not repeat unless another
bpf_timer_start() is made. In such case the next invoca-
tion can migrate to a different cpu. Since struct
bpf_timer is a field inside map element the map owns the
timer. The bpf_timer_set_callback() will increment refcnt
of BPF program to make sure that callback_fn code stays
valid. When user space reference to a map reaches zero
all timers in a map are cancelled and corresponding pro-
gram's refcnts are decremented. This is done to make sure
that Ctrl-C of a user process doesn't leave any timers
running. If map is pinned in bpffs the callback_fn can
re-arm itself indefinitely. bpf_map_update/delete_elem()
helpers and user space sys_bpf commands cancel and free
the timer in the given map element. The map can contain
timers that invoke callback_fn-s from different programs.
The same callback_fn can serve different timers from dif-
ferent maps if key/value layout matches across maps.
Every bpf_timer_set_callback() can have different call-
back_fn.
flags can be one of:
BPF_F_TIMER_ABS
Start the timer in absolute expire value instead
of the default relative one.
BPF_F_TIMER_CPU_PIN
Timer will be pinned to the CPU of the caller.
Return 0 on success. -EINVAL if timer was not initialized with
bpf_timer_init() earlier or invalid flags are passed.
long bpf_timer_cancel(struct bpf_timer *timer)
Description
Cancel the timer and wait for callback_fn to finish if it
was running.
Return 0 if the timer was not active. 1 if the timer was ac-
tive. -EINVAL if timer was not initialized with
bpf_timer_init() earlier. -EDEADLK if callback_fn tried
to call bpf_timer_cancel() on its own timer which would
have led to a deadlock otherwise.
u64 bpf_get_func_ip(void *ctx)
Description
Get address of the traced function (for tracing and
kprobe programs).
When called for kprobe program attached as uprobe it re-
turns probe address for both entry and return uprobe.
Return Address of the traced function for kprobe. 0 for kprobes
placed within the function (not at the entry). Address
of the probe for uprobe and return uprobe.
u64 bpf_get_attach_cookie(void *ctx)
Description
Get bpf_cookie value provided (optionally) during the
program attachment. It might be different for each indi-
vidual attachment, even if BPF program itself is the
same. Expects BPF program context ctx as a first argu-
ment.
Supported for the following program types:
• kprobe/uprobe;
• tracepoint;
• perf_event.
Return Value specified by user at BPF link creation/attachment
time or 0, if it was not specified.
long bpf_task_pt_regs(struct task_struct *task)
Description
Get the struct pt_regs associated with task.
Return A pointer to struct pt_regs.
long bpf_get_branch_snapshot(void *entries, u32 size, u64 flags)
Description
Get branch trace from hardware engines like Intel LBR.
The hardware engine is stopped shortly after the helper
is called. Therefore, the user need to filter branch en-
tries based on the actual use case. To capture branch
trace before the trigger point of the BPF program, the
helper should be called at the beginning of the BPF pro-
gram.
The data is stored as struct perf_branch_entry into out-
put buffer entries. size is the size of entries in bytes.
flags is reserved for now and must be zero.
Return On success, number of bytes written to buf. On error, a
negative value.
-EINVAL if flags is not zero.
-ENOENT if architecture does not support branch records.
long bpf_trace_vprintk(const char *fmt, u32 fmt_size, const void *data,
u32 data_len)
Description
Behaves like bpf_trace_printk() helper, but takes an ar-
ray of u64 to format and can handle more format args as a
result.
Arguments are to be used as in bpf_seq_printf() helper.
Return The number of bytes written to the buffer, or a negative
error in case of failure.
struct unix_sock *bpf_skc_to_unix_sock(void *sk)
Description
Dynamically cast a sk pointer to a unix_sock pointer.
Return sk if casting is valid, or NULL otherwise.
long bpf_kallsyms_lookup_name(const char *name, int name_sz, int flags,
u64 *res)
Description
Get the address of a kernel symbol, returned in res. res
is set to 0 if the symbol is not found.
Return On success, zero. On error, a negative value.
-EINVAL if flags is not zero.
-EINVAL if string name is not the same size as name_sz.
-ENOENT if symbol is not found.
-EPERM if caller does not have permission to obtain ker-
nel address.
long bpf_find_vma(struct task_struct *task, u64 addr, void *call-
back_fn, void *callback_ctx, u64 flags)
Description
Find vma of task that contains addr, call callback_fn
function with task, vma, and callback_ctx. The call-
back_fn should be a static function and the callback_ctx
should be a pointer to the stack. The flags is used to
control certain aspects of the helper. Currently, the
flags must be 0.
The expected callback signature is
long (*callback_fn)(struct task_struct *task, struct
vm_area_struct *vma, void *callback_ctx);
Return 0 on success. -ENOENT if task->mm is NULL, or no vma
contains addr. -EBUSY if failed to try lock mmap_lock.
-EINVAL for invalid flags.
long bpf_loop(u32 nr_loops, void *callback_fn, void *callback_ctx, u64
flags)
Description
For nr_loops, call callback_fn function with callback_ctx
as the context parameter. The callback_fn should be a
static function and the callback_ctx should be a pointer
to the stack. The flags is used to control certain as-
pects of the helper. Currently, the flags must be 0.
Currently, nr_loops is limited to 1 << 23 (~8 million)
loops.
long (*callback_fn)(u32 index, void *ctx);
where index is the current index in the loop. The index
is zero-indexed.
If callback_fn returns 0, the helper will continue to the
next loop. If return value is 1, the helper will skip the
rest of the loops and return. Other return values are not
used now, and will be rejected by the verifier.
Return The number of loops performed, -EINVAL for invalid flags,
-E2BIG if nr_loops exceeds the maximum number of loops.
long bpf_strncmp(const char *s1, u32 s1_sz, const char *s2)
Description
Do strncmp() between s1 and s2. s1 doesn't need to be
null-terminated and s1_sz is the maximum storage size of
s1. s2 must be a read-only string.
Return An integer less than, equal to, or greater than zero if
the first s1_sz bytes of s1 is found to be less than, to
match, or be greater than s2.
long bpf_get_func_arg(void *ctx, u32 n, u64 *value)
Description
Get n-th argument register (zero based) of the traced
function (for tracing programs) returned in value.
Return 0 on success. -EINVAL if n >= argument register count of
traced function.
long bpf_get_func_ret(void *ctx, u64 *value)
Description
Get return value of the traced function (for tracing pro-
grams) in value.
Return 0 on success. -EOPNOTSUPP for tracing programs other
than BPF_TRACE_FEXIT or BPF_MODIFY_RETURN.
long bpf_get_func_arg_cnt(void *ctx)
Description
Get number of registers of the traced function (for trac-
ing programs) where function arguments are stored in
these registers.
Return The number of argument registers of the traced function.
int bpf_get_retval(void)
Description
Get the BPF program's return value that will be returned
to the upper layers.
This helper is currently supported by cgroup programs and
only by the hooks where BPF program's return value is re-
turned to the userspace via errno.
Return The BPF program's return value.
int bpf_set_retval(int retval)
Description
Set the BPF program's return value that will be returned
to the upper layers.
This helper is currently supported by cgroup programs and
only by the hooks where BPF program's return value is re-
turned to the userspace via errno.
Note that there is the following corner case where the
program exports an error via bpf_set_retval but signals
success via 'return 1':
bpf_set_retval(-EPERM); return 1;
In this case, the BPF program's return value will use
helper's -EPERM. This still holds true for
cgroup/bind{4,6} which supports extra 'return 3' success
case.
Return 0 on success, or a negative error in case of failure.
u64 bpf_xdp_get_buff_len(struct xdp_buff *xdp_md)
Description
Get the total size of a given xdp buff (linear and paged
area)
Return The total size of a given xdp buffer.
long bpf_xdp_load_bytes(struct xdp_buff *xdp_md, u32 offset, void *buf,
u32 len)
Description
This helper is provided as an easy way to load data from
a xdp buffer. It can be used to load len bytes from off-
set from the frame associated to xdp_md, into the buffer
pointed by buf.
Return 0 on success, or a negative error in case of failure.
long bpf_xdp_store_bytes(struct xdp_buff *xdp_md, u32 offset, void
*buf, u32 len)
Description
Store len bytes from buffer buf into the frame associated
to xdp_md, at offset.
Return 0 on success, or a negative error in case of failure.
long bpf_copy_from_user_task(void *dst, u32 size, const void *user_ptr,
struct task_struct *tsk, u64 flags)
Description
Read size bytes from user space address user_ptr in tsk's
address space, and stores the data in dst. flags is not
used yet and is provided for future extensibility. This
helper can only be used by sleepable programs.
Return 0 on success, or a negative error in case of failure. On
error dst buffer is zeroed out.
long bpf_skb_set_tstamp(struct sk_buff *skb, u64 tstamp, u32
tstamp_type)
Description
Change the __sk_buff->tstamp_type to tstamp_type and set
tstamp to the __sk_buff->tstamp together.
If there is no need to change the __sk_buff->tstamp_type,
the tstamp value can be directly written to
__sk_buff->tstamp instead.
BPF_SKB_TSTAMP_DELIVERY_MONO is the only tstamp that will
be kept during bpf_redirect_*(). A non zero tstamp must
be used with the BPF_SKB_TSTAMP_DELIVERY_MONO
tstamp_type.
A BPF_SKB_TSTAMP_UNSPEC tstamp_type can only be used with
a zero tstamp.
Only IPv4 and IPv6 skb->protocol are supported.
This function is most useful when it needs to set a mono
delivery time to __sk_buff->tstamp and then bpf_redi-
rect_*() to the egress of an iface. For example, chang-
ing the (rcv) timestamp in __sk_buff->tstamp at ingress
to a mono delivery time and then bpf_redirect_*() to
sch_fq@phy-dev.
Return 0 on success. -EINVAL for invalid input -EOPNOTSUPP for
unsupported protocol
long bpf_ima_file_hash(struct file *file, void *dst, u32 size)
Description
Returns a calculated IMA hash of the file. If the hash
is larger than size, then only size bytes will be copied
to dst
Return The hash_algo is returned on success, -EOPNOTSUP if the
hash calculation failed or -EINVAL if invalid arguments
are passed.
void *bpf_kptr_xchg(void *map_value, void *ptr)
Description
Exchange kptr at pointer map_value with ptr, and return
the old value. ptr can be NULL, otherwise it must be a
referenced pointer which will be released when this
helper is called.
Return The old value of kptr (which can be NULL). The returned
pointer if not NULL, is a reference which must be re-
leased using its corresponding release function, or moved
into a BPF map before program exit.
void *bpf_map_lookup_percpu_elem(struct bpf_map *map, const void *key,
u32 cpu)
Description
Perform a lookup in percpu map for an entry associated to
key on cpu.
Return Map value associated to key on cpu, or NULL if no entry
was found or cpu is invalid.
struct mptcp_sock *bpf_skc_to_mptcp_sock(void *sk)
Description
Dynamically cast a sk pointer to a mptcp_sock pointer.
Return sk if casting is valid, or NULL otherwise.
long bpf_dynptr_from_mem(void *data, u32 size, u64 flags, struct
bpf_dynptr *ptr)
Description
Get a dynptr to local memory data.
data must be a ptr to a map value. The maximum size sup-
ported is DYNPTR_MAX_SIZE. flags is currently unused.
Return 0 on success, -E2BIG if the size exceeds DYNPTR_MAX_SIZE,
-EINVAL if flags is not 0.
long bpf_ringbuf_reserve_dynptr(void *ringbuf, u32 size, u64 flags,
struct bpf_dynptr *ptr)
Description
Reserve size bytes of payload in a ring buffer ringbuf
through the dynptr interface. flags must be 0.
Please note that a corresponding bpf_ringbuf_sub-
mit_dynptr or bpf_ringbuf_discard_dynptr must be called
on ptr, even if the reservation fails. This is enforced
by the verifier.
Return 0 on success, or a negative error in case of failure.
void bpf_ringbuf_submit_dynptr(struct bpf_dynptr *ptr, u64 flags)
Description
Submit reserved ring buffer sample, pointed to by data,
through the dynptr interface. This is a no-op if the
dynptr is invalid/null.
For more information on flags, please see 'bpf_ring-
buf_submit'.
Return Nothing. Always succeeds.
void bpf_ringbuf_discard_dynptr(struct bpf_dynptr *ptr, u64 flags)
Description
Discard reserved ring buffer sample through the dynptr
interface. This is a no-op if the dynptr is invalid/null.
For more information on flags, please see 'bpf_ring-
buf_discard'.
Return Nothing. Always succeeds.
long bpf_dynptr_read(void *dst, u32 len, const struct bpf_dynptr *src,
u32 offset, u64 flags)
Description
Read len bytes from src into dst, starting from offset
into src. flags is currently unused.
Return 0 on success, -E2BIG if offset + len exceeds the length
of src's data, -EINVAL if src is an invalid dynptr or if
flags is not 0.
long bpf_dynptr_write(const struct bpf_dynptr *dst, u32 offset, void
*src, u32 len, u64 flags)
Description
Write len bytes from src into dst, starting from offset
into dst.
flags must be 0 except for skb-type dynptrs.
For skb-type dynptrs:
• All data slices of the dynptr are automatically
invalidated after bpf_dynptr_write(). This is
because writing may pull the skb and change the
underlying packet buffer.
• For flags, please see the flags accepted by
bpf_skb_store_bytes().
Return 0 on success, -E2BIG if offset + len exceeds the length
of dst's data, -EINVAL if dst is an invalid dynptr or if
dst is a read-only dynptr or if flags is not correct. For
skb-type dynptrs, other errors correspond to errors re-
turned by bpf_skb_store_bytes().
void *bpf_dynptr_data(const struct bpf_dynptr *ptr, u32 offset, u32
len)
Description
Get a pointer to the underlying dynptr data.
len must be a statically known value. The returned data
slice is invalidated whenever the dynptr is invalidated.
skb and xdp type dynptrs may not use bpf_dynptr_data.
They should instead use bpf_dynptr_slice and
bpf_dynptr_slice_rdwr.
Return Pointer to the underlying dynptr data, NULL if the dynptr
is read-only, if the dynptr is invalid, or if the offset
and length is out of bounds.
s64 bpf_tcp_raw_gen_syncookie_ipv4(struct iphdr *iph, struct tcphdr
*th, u32 th_len)
Description
Try to issue a SYN cookie for the packet with correspond-
ing IPv4/TCP headers, iph and th, without depending on a
listening socket.
iph points to the IPv4 header.
th points to the start of the TCP header, while th_len
contains the length of the TCP header (at least
sizeof(struct tcphdr)).
Return On success, lower 32 bits hold the generated SYN cookie
in followed by 16 bits which hold the MSS value for that
cookie, and the top 16 bits are unused.
On failure, the returned value is one of the following:
-EINVAL if th_len is invalid.
s64 bpf_tcp_raw_gen_syncookie_ipv6(struct ipv6hdr *iph, struct tcphdr
*th, u32 th_len)
Description
Try to issue a SYN cookie for the packet with correspond-
ing IPv6/TCP headers, iph and th, without depending on a
listening socket.
iph points to the IPv6 header.
th points to the start of the TCP header, while th_len
contains the length of the TCP header (at least
sizeof(struct tcphdr)).
Return On success, lower 32 bits hold the generated SYN cookie
in followed by 16 bits which hold the MSS value for that
cookie, and the top 16 bits are unused.
On failure, the returned value is one of the following:
-EINVAL if th_len is invalid.
-EPROTONOSUPPORT if CONFIG_IPV6 is not builtin.
long bpf_tcp_raw_check_syncookie_ipv4(struct iphdr *iph, struct tcphdr
*th)
Description
Check whether iph and th contain a valid SYN cookie ACK
without depending on a listening socket.
iph points to the IPv4 header.
th points to the TCP header.
Return 0 if iph and th are a valid SYN cookie ACK.
On failure, the returned value is one of the following:
-EACCES if the SYN cookie is not valid.
long bpf_tcp_raw_check_syncookie_ipv6(struct ipv6hdr *iph, struct
tcphdr *th)
Description
Check whether iph and th contain a valid SYN cookie ACK
without depending on a listening socket.
iph points to the IPv6 header.
th points to the TCP header.
Return 0 if iph and th are a valid SYN cookie ACK.
On failure, the returned value is one of the following:
-EACCES if the SYN cookie is not valid.
-EPROTONOSUPPORT if CONFIG_IPV6 is not builtin.
u64 bpf_ktime_get_tai_ns(void)
Description
A nonsettable system-wide clock derived from wall-clock
time but ignoring leap seconds. This clock does not ex-
perience discontinuities and backwards jumps caused by
NTP inserting leap seconds as CLOCK_REALTIME does.
See: clock_gettime(CLOCK_TAI)
Return Current ktime.
long bpf_user_ringbuf_drain(struct bpf_map *map, void *callback_fn,
void *ctx, u64 flags)
Description
Drain samples from the specified user ring buffer, and
invoke the provided callback for each such sample:
long (*callback_fn)(const struct bpf_dynptr *dynptr, void
*ctx);
If callback_fn returns 0, the helper will continue to try
and drain the next sample, up to a maximum of
BPF_MAX_USER_RINGBUF_SAMPLES samples. If the return value
is 1, the helper will skip the rest of the samples and
return. Other return values are not used now, and will be
rejected by the verifier.
Return The number of drained samples if no error was encountered
while draining samples, or 0 if no samples were present
in the ring buffer. If a user-space producer was
epoll-waiting on this map, and at least one sample was
drained, they will receive an event notification notify-
ing them of available space in the ring buffer. If the
BPF_RB_NO_WAKEUP flag is passed to this function, no
wakeup notification will be sent. If the
BPF_RB_FORCE_WAKEUP flag is passed, a wakeup notification
will be sent even if no sample was drained.
On failure, the returned value is one of the following:
-EBUSY if the ring buffer is contended, and another call-
ing context was concurrently draining the ring buffer.
-EINVAL if user-space is not properly tracking the ring
buffer due to the producer position not being aligned to
8 bytes, a sample not being aligned to 8 bytes, or the
producer position not matching the advertised length of a
sample.
-E2BIG if user-space has tried to publish a sample which
is larger than the size of the ring buffer, or which can-
not fit within a struct bpf_dynptr.
void *bpf_cgrp_storage_get(struct bpf_map *map, struct cgroup *cgroup,
void *value, u64 flags)
Description
Get a bpf_local_storage from the cgroup.
Logically, it could be thought of as getting the value
from a map with cgroup as the key. From this perspec-
tive, the usage is not much different from
bpf_map_lookup_elem(map, &cgroup) except this helper en-
forces the key must be a cgroup struct and the map must
also be a BPF_MAP_TYPE_CGRP_STORAGE.
In reality, the local-storage value is embedded directly
inside of the cgroup object itself, rather than being lo-
cated in the BPF_MAP_TYPE_CGRP_STORAGE map. When the lo-
cal-storage value is queried for some map on a cgroup ob-
ject, the kernel will perform an O(n) iteration over all
of the live local-storage values for that cgroup object
until the local-storage value for the map is found.
An optional flags (BPF_LOCAL_STORAGE_GET_F_CREATE) can be
used such that a new bpf_local_storage will be created if
one does not exist. value can be used together with
BPF_LOCAL_STORAGE_GET_F_CREATE to specify the initial
value of a bpf_local_storage. If value is NULL, the new
bpf_local_storage will be zero initialized.
Return A bpf_local_storage pointer is returned on success.
NULL if not found or there was an error in adding a new
bpf_local_storage.
long bpf_cgrp_storage_delete(struct bpf_map *map, struct cgroup
*cgroup)
Description
Delete a bpf_local_storage from a cgroup.
Return 0 on success.
-ENOENT if the bpf_local_storage cannot be found.
EXAMPLES
Example usage for most of the eBPF helpers listed in this manual page
are available within the Linux kernel sources, at the following loca-
tions:
• samples/bpf/
• tools/testing/selftests/bpf/
LICENSE
eBPF programs can have an associated license, passed along with the
bytecode instructions to the kernel when the programs are loaded. The
format for that string is identical to the one in use for kernel mod-
ules (Dual licenses, such as "Dual BSD/GPL", may be used). Some helper
functions are only accessible to programs that are compatible with the
GNU General Public License (GNU GPL).
In order to use such helpers, the eBPF program must be loaded with the
correct license string passed (via attr) to the bpf() system call, and
this generally translates into the C source code of the program con-
taining a line similar to the following:
char ____license[] __attribute__((section("license"), used)) = "GPL";
IMPLEMENTATION
This manual page is an effort to document the existing eBPF helper
functions. But as of this writing, the BPF sub-system is under heavy
development. New eBPF program or map types are added, along with new
helper functions. Some helpers are occasionally made available for ad-
ditional program types. So in spite of the efforts of the community,
this page might not be up-to-date. If you want to check by yourself
what helper functions exist in your kernel, or what types of programs
they can support, here are some files among the kernel tree that you
may be interested in:
• include/uapi/linux/bpf.h is the main BPF header. It contains the full
list of all helper functions, as well as many other BPF definitions
including most of the flags, structs or constants used by the
helpers.
• net/core/filter.c contains the definition of most network-related
helper functions, and the list of program types from which they can
be used.
• kernel/trace/bpf_trace.c is the equivalent for most tracing pro-
gram-related helpers.
• kernel/bpf/verifier.c contains the functions used to check that valid
types of eBPF maps are used with a given helper function.
• kernel/bpf/ directory contains other files in which additional
helpers are defined (for cgroups, sockmaps, etc.).
• The bpftool utility can be used to probe the availability of helper
functions on the system (as well as supported program and map types,
and a number of other parameters). To do so, run bpftool feature
probe (see bpftool-feature(8) for details). Add the unprivileged key-
word to list features available to unprivileged users.
Compatibility between helper functions and program types can generally
be found in the files where helper functions are defined. Look for the
struct bpf_func_proto objects and for functions returning them: these
functions contain a list of helpers that a given program type can call.
Note that the default: label of the switch ... case used to filter
helpers can call other functions, themselves allowing access to addi-
tional helpers. The requirement for GPL license is also in those struct
bpf_func_proto.
Compatibility between helper functions and map types can be found in
the check_map_func_compatibility() function in file kernel/bpf/veri-
fier.c.
Helper functions that invalidate the checks on data and data_end point-
ers for network processing are listed in function
bpf_helper_changes_pkt_data() in file net/core/filter.c.
SEE ALSO
bpf(2), bpftool(8), cgroups(7), ip(8), perf_event_open(2), sendmsg(2),
socket(7), tc-bpf(8)
Linux v6.8 2023-11-10 BPF-HELPERS(7)
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