SYSTEMD-PCRLOCK(8) systemd-pcrlock SYSTEMD-PCRLOCK(8)
NAME
systemd-pcrlock, systemd-pcrlock-file-system.service, systemd-pcrlock-
firmware-code.service, systemd-pcrlock-firmware-config.service,
systemd-pcrlock-machine-id.service, systemd-pcrlock-make-
policy.service, systemd-pcrlock-secureboot-authority.service, systemd-
pcrlock-secureboot-policy.service - Analyze and predict TPM2 PCR states
and generate an access policy from the prediction
SYNOPSIS
/usr/lib/systemd/systemd-pcrlock [OPTIONS...]
DESCRIPTION
Note: this command is experimental for now. While it is likely to
become a regular component of systemd, it might still change in
behaviour and interface.
systemd-pcrlock is a tool that may be used to analyze and predict TPM2
PCR measurements, and generate TPM2 access policies from the prediction
which it stores in a TPM2 NV index (i.e. in the TPM2 non-volatile
memory). This may then be used to restrict access to TPM2 objects (such
as disk encryption keys) to system boot-ups in which only specific,
trusted components are used.
systemd-pcrlock uses as input for its analysis and prediction:
• The UEFI firmware TPM2 event log (i.e.
/sys/kernel/security/tpm0/binary_bios_measurements) of the current
boot.
• The userspace TPM2 event log (i.e.
/run/log/systemd/tpm2-measure.log) of the current boot.
• The current PCR state of the TPM2 chip.
• Boot component definition files (*.pcrlock and
*.pcrlock.d/*.pcrlock, see systemd.pcrlock(5)) that each define
expected measurements for one component of the boot process,
permitting alternative variants for each. (Variants may be used
used to bless multiple kernel versions or boot loader versions at
the same time.)
It uses these inputs to generate a combined event log, validating it
against the PCR states. It then attempts to recognize event log records
and matches them against the defined components. For each PCR where
this can be done comprehensively (i.e. where all listed records and all
defined components have been matched) this may then be used to predict
future PCR measurements, taking the alternative variants defined for
each component into account. This prediction may then be converted into
a TPM2 access policy (consisting of TPM2 PolicyPCR and PolicyOR items),
which is then stored in an NV index in the TPM2. This may be used to
then lock secrets (such as disk encryption keys) to these policies (via
a TPM2 PolicyAuthorizeNV policy).
Use tools such as systemd-cryptenroll(1) or systemd-repart(8) to bind
disk encryption to such a systemd-pcrlock TPM2 policy. Specifically,
see the --tpm2-pcrlock= switches of these tools.
The access policy logic requires a TPM2 device that implements the
"PolicyAuthorizeNV" command, i.e. implements TPM 2.0 version 1.38 or
newer.
COMMANDS
The following commands are understood:
log
This reads the combined TPM2 event log, validates it, matches it
against the current PCR values, and outputs both in tabular form.
Combine with --json= to generate output in JSON format.
Added in version 255.
cel
This reads the combined TPM2 event log and writes it to STDOUT in
TCG Common Event Log Format (CEL-JSON)[1] format.
Added in version 255.
list-components
Shows a list of component definitions and their variants, i.e. the
*.pcrlock files discovered in /var/lib/pcrlock.d/,
/usr/lib/pcrlock.d/, and the other supported directories. See
systemd.pcrlock(5) for details on these files and the full list of
directories searched.
Added in version 255.
predict
Predicts the PCR state on future boots. This will analyze the TPM2
event log as described above, recognize components, and then
generate all possible resulting PCR values for all combinations of
component variants. Note that no prediction is made for PCRs whose
value does not match the event log records, for which unrecognized
measurements are discovered or for which components are defined
that cannot be found in the event log. This is a safety measure to
ensure that any generated access policy can be fulfilled correctly
on current and future boots.
Added in version 255.
make-policy
This predicts the PCR state for future boots, much like the predict
command above. It then uses this data to generate a TPM2 access
policy which it stores in a TPM2 NV index. The prediction and
information about the used TPM2 and its NV index are written to
/var/lib/systemd/pcrlock.json.
The NV index is allocated on first invocation, and updated on
subsequent invocations.
The NV index contents may be changed (and thus the policy stored in
it updated) by providing an access PIN. This PIN is normally
generated automatically and stored in encrypted form (with an
access policy binding it to the NV index itself) in the
aforementioned JSON policy file. This PIN may be chosen by the
user, via the --recovery-pin= switch. If specified it may be used
as alternative path of access to update the policy.
If the new prediction matches the old this command terminates
quickly and executes no further operation. (Unless --force is
specified, see below.)
Added in version 255.
remove-policy
Removes a previously generated policy. Deletes the
/var/lib/systemd/pcrlock.json file, and deallocates the NV index.
Added in version 255.
lock-firmware-code, unlock-firmware-code
Generates/removes .pcrlock files based on the TPM2 event log of the
current boot covering all records for PCRs 0 ("platform-code") and
2 ("external-code").
This operation allows locking the boot process to the current
version of the firmware of the system and its extension cards. This
operation should only be used if the system vendor does not provide
suitable pcrlock data ahead of time.
Note that this data only matches the current version of the
firmware. If a firmware update is applied this data will be
out-of-date and any access policy generated from it will no longer
pass. It is thus recommended to invoke unlock-firmware-code before
doing a firmware update, followed by make-policy to refresh the
policy.
systemd-pcrlock lock-firmware-code is invoked automatically at boot
via the systemd-pcrlock-firmware-code.service unit, if enabled.
This ensures that an access policy managed by systemd-pcrlock is
automatically locked to the new firmware version whenever the
policy has been relaxed temporarily, in order to cover for firmware
updates, as described above.
The files are only generated from the event log if the event log
matches the current TPM2 PCR state.
This writes/removes the files
/var/lib/pcrlock.d/250-firmware-code-early.pcrlock.d/generated.pcrlock
and
/var/lib/pcrlock.d/550-firmware-code-late.pcrlock.d/generated.pcrlock.
Added in version 255.
lock-firmware-config, unlock-firmware-config
This is similar to lock-firmware-code/unlock-firmware-code but
locks down the firmware configuration, i.e. PCRs 1
("platform-config") and 3 ("external-config").
This functionality should be used with care as in most scenarios a
minor firmware configuration change should not invalidate access
policies to TPM2 objects. Also note that some systems measure
unstable and unpredictable information (e.g. current CPU voltages,
temperatures, as part of SMBIOS data) to these PCRs, which means
this form of lockdown cannot be used reliably on such systems. Use
this functionality only if the system and hardware is well known
and does not suffer by these limitations, for example in
virtualized environments.
Use unlock-firmware-config before making firmware configuration
changes. If the systemd-pcrlock-firmware-config.service unit is
enabled it will automatically generate a pcrlock file from the new
measurements.
This writes/removes the files
/var/lib/pcrlock.d/250-firmware-config-early.pcrlock.d/generated.pcrlock
and
/var/lib/pcrlock.d/550-firmware-config-late.pcrlock.d/generated.pcrlock.
Added in version 255.
lock-secureboot-policy, unlock-secureboot-policy
Generates/removes a .pcrlock file based on the SecureBoot policy
currently enforced. This looks at the SecureBoot, PK, KEK, db, dbx,
dbt, dbr EFI variables and predicts their measurements to PCR 7
("secure-boot-policy") on the next boot.
Use unlock-firmware-config before applying SecureBoot policy
updates. If the systemd-pcrlock-secureboot-policy.service unit is
enabled it will automatically generate a pcrlock file from the
policy discovered.
This writes/removes the file
/var/lib/pcrlock.d/230-secureboot-policy.pcrlock.d/generated.pcrlock.
Added in version 255.
lock-secureboot-authority, unlock-secureboot-authority
Generates/removes a .pcrlock file based on the SecureBoot
authorities used to validate the boot path. SecureBoot authorities
are the specific SecureBoot database entries that where used to
validate the UEFI PE binaries executed at boot. This looks at the
event log of the current boot, and uses relevant measurements on
PCR 7 ("secure-boot-policy").
This writes/removes the file
/var/lib/pcrlock.d/620-secureboot-authority.pcrlock.d/generated.pcrlock.
Added in version 255.
lock-gpt [DEVICE], unlock-gpt
Generates/removes a .pcrlock file based on the GPT partition table
of the specified disk. If no disk is specified automatically
determines the block device backing the root file system. This
locks the state of the disk partitioning of the booted medium,
which firmware measures to PCR 5 ("boot-loader-config").
This writes/removes the file
/var/lib/pcrlock.d/600-gpt.pcrlock.d/generated.pcrlock.
Added in version 255.
lock-pe [BINARY], unlock-pe
Generates/removes a .pcrlock file based on the specified PE binary.
This is useful for predicting measurements the firmware makes to
PCR 4 ("boot-loader-code") if the specified binary is part of the
UEFI boot process. Use this on boot loader binaries and suchlike.
Use lock-uki (see below) for PE binaries that are unified kernel
images (UKIs).
Expects a path to the PE binary as argument. If not specified,
reads the binary from STDIN instead.
The pcrlock file to write must be specified via the --pcrlock=
switch.
Added in version 255.
lock-uki [UKI], unlock-uki
Generates/removes a .pcrlock file based on the specified UKI PE
binary. This is useful for predicting measurements the firmware
makes to PCR 4 ("boot-loader-code"), and systemd-stub(7) makes to
PCR 11 ("kernel-boot"), if the specified UKI is booted. This is a
superset of lock-pe.
Expects a path to the UKI PE binary as argument. If not specified,
reads the binary from STDIN instead.
The pcrlock file to write must be specified via the --pcrlock=
switch.
Added in version 255.
lock-machine-id, unlock-machine-id
Generates/removes a .pcrlock file based on /etc/machine-id. This is
useful for predicting measurements systemd-pcrmachine.service(8)
makes to PCR 15 ("system-identity").
This writes/removes the file
/var/lib/pcrlock.d/820-machine-id.pcrlock.
Added in version 255.
lock-file-system [PATH], unlock-file-system [PATH]
Generates/removes a .pcrlock file based on file system identity.
This is useful for predicting measurements systemd-
pcrfs@.service(8) makes to PCR 15 ("system-identity") for the root
and /var/ file systems.
This writes/removes the files
/var/lib/pcrlock.d/830-root-file-system.pcrlock and
/var/lib/pcrlock.d/840-file-system-path.pcrlock.
Added in version 255.
lock-kernel-cmdline [FILE], unlock-kernel-cmdline
Generates/removes a .pcrlock file based on /proc/cmdline (or the
specified file if given). This is useful for predicting
measurements the Linux kernel makes to PCR 9 ("kernel-initrd").
This writes/removes the file
/var/lib/pcrlock.d/710-kernel-cmdline.pcrlock/generated.pcrlock.
Added in version 255.
lock-kernel-initrd FILE, unlock-kernel-initrd
Generates/removes a .pcrlock file based on a kernel initrd cpio
archive. This is useful for predicting measurements the Linux
kernel makes to PCR 9 ("kernel-initrd"). Do not use for
systemd-stub UKIs, as the initrd is combined dynamically from
various sources and hence does not take a single input, like this
command.
This writes/removes the file
/var/lib/pcrlock.d/720-kernel-initrd.pcrlock/generated.pcrlock.
Added in version 255.
lock-raw [FILE], unlock-raw
Generates/removes a .pcrlock file based on raw binary data. The
data is either read from the specified file or from STDIN (if none
is specified). This requires that --pcrs= is specified. The
generated pcrlock file is written to the file specified via
--pcrlock= or to STDOUT (if none is specified).
Added in version 255.
OPTIONS
The following options are understood:
--raw-description
When displaying the TPM2 event log do not attempt to decode the
records to provide a friendly event log description string.
Instead, show the binary payload data in escaped form.
Added in version 255.
--pcr=
Specifies the PCR number to use. May be specified more than once to
select multiple PCRs.
This is used by lock-raw and lock-pe to select the PCR to lock
against.
If used with predict and make-policy this will override which PCRs
to include in the prediction and policy. If unspecified this
defaults to PCRs 0-5, 7, 11-15. Note that these commands will not
include any PCRs in the prediction/policy (even if specified
explicitly) if there are measurements in the event log that do not
match the current PCR value, or there are unrecognized measurements
in the event log, or components define measurements not seen in the
event log.
Added in version 255.
--nv-index=
Specifies to NV index to store the policy in. Honoured by
make-policy. If not specified the command will automatically pick a
free NV index.
Added in version 255.
--components=
Takes a path to read *.pcrlock and *.pcrlock.d/*.pcrlock files
from. May be used more than once to specify multiple such
directories. If not specified defaults to /etc/pcrlock.d/,
/run/pcrlock.d/, /var/lib/pcrlock.d/, /usr/local/pcrlock.d/,
/usr/lib/pcrlock.d/.
Added in version 255.
--location=
Takes either a string or a colon-separated pair of strings.
Configures up to which point in the sorted list of defined
components to analyze/predict PCRs to. Typically, the
systemd-pcrlock tool is invoked from a fully booted system after
boot-up and before shutdown. This means various components that are
defined for shutdown have not been measured yet, and should not be
searched for. This option allows one to restrict which components
are considered for analysis (taking only components before some
point into account, ignoring components after them). The expected
string is ordered against the filenames of the components defined.
Any components with a lexicographically later name are ignored.
This logic applies to the log, predict, and make-policy verbs. If a
colon-separated pair of strings are specified then they select
which phases of the boot to include in the prediction/policy. The
first string defines where the first prediction shall be made, and
the second string defines where the last prediction shall be made.
All such predictions are then combined into one set.
If used with list-components the selected location range will be
highlighted in the component list.
Defaults to "760-:940-", which means the policies generated by
default will basically cover the whole runtime of the OS userspace,
from the initrd (as "760-" closely follows
750-enter-initrd.pcrlock) until (and including) the main runtime of
the system (as "940-" is closely followed by 950-shutdown.pcrlock).
See systemd.pcrlock(5) for a full list of well-known components,
that illustrate where this range is placed by default.
Added in version 255.
--recovery-pin=
Takes a boolean. Defaults to false. Honoured by make-policy. If
true, will query the user for a PIN to unlock the TPM2 NV index
with. If no policy was created before this PIN is used to protect
the newly allocated NV index. If a policy has been created before
the PIN is used to unlock write access to the NV index. If this
option is not used a PIN is automatically generated. Regardless if
user supplied or automatically generated, it is stored in encrypted
form in the policy metadata file. The recovery PIN may be used to
regain write access to an NV index in case the access policy became
out of date.
Added in version 255.
--pcrlock=
Takes a file system path as argument. If specified overrides where
to write the generated pcrlock data to. Honoured by the various
lock-* commands. If not specified, a default path is generally
used, as documented above.
Added in version 255.
--policy=
Takes a file system path as argument. If specified overrides where
to write pcrlock policy metadata to. If not specified defaults to
/var/lib/systemd/pcrlock.json.
Added in version 255.
--force
If specified with make-policy, the predicted policy will be written
to the NV index even if it is detected to be the same as the
previously stored one.
Added in version 255.
--json=MODE
Shows output formatted as JSON. Expects one of "short" (for the
shortest possible output without any redundant whitespace or line
breaks), "pretty" (for a pretty version of the same, with
indentation and line breaks) or "off" (to turn off JSON output, the
default).
--no-pager
Do not pipe output into a pager.
-h, --help
Print a short help text and exit.
--version
Print a short version string and exit.
EXIT STATUS
On success, 0 is returned, a non-zero failure code otherwise.
SEE ALSO
systemd(1), systemd.pcrlock(5), systemd-cryptenroll(1), systemd-
cryptsetup@.service(8), systemd-repart(8), systemd-
pcrmachine.service(8)
NOTES
1. TCG Common Event Log Format (CEL-JSON)
https://trustedcomputinggroup.org/resource/canonical-event-log-format/
systemd 255 SYSTEMD-PCRLOCK(8)
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