SYSTEMD-PCRPHASE.SERVICE(8)systemd-pcrphase.serviceSYSTEMD-PCRPHASE.SERVICE(8)
NAME
systemd-pcrphase.service, systemd-pcrphase-sysinit.service, systemd-
pcrphase-initrd.service, systemd-pcrphase - Measure boot phase into
TPM2 PCR 11
SYNOPSIS
systemd-pcrphase.service
systemd-pcrphase-sysinit.service
systemd-pcrphase-initrd.service
/lib/systemd/system-pcrphase STRING
DESCRIPTION
systemd-pcrphase.service, systemd-pcrphase-sysinit.service and
systemd-pcrphase-initrd.service are system services that measure
specific strings into TPM2 PCR 11 during boot at various milestones of
the boot process.
These services require systemd-stub(7) to be used in a unified kernel
image (UKI) setup. They execute no operation when invoked when the stub
has not been used to invoke the kernel. The stub will measure the
invoked kernel and associated vendor resources into PCR 11 before
handing control to it; once userspace is invoked these services then
will extend certain literal strings indicating various phases of the
boot process into TPM2 PCR 11. During a regular boot process the
following strings are extended into PCR 11.
1. "enter-initrd" is extended into PCR 11 early when the initrd
initializes, before activating system extension images for the
initrd. It is supposed to act as barrier between the time where the
kernel initializes, and where the initrd starts operating and
enables system extension images, i.e. code shipped outside of the
UKI. (This string is extended at start of
systemd-pcrphase-initrd.service.)
2. "leave-initrd" is extended into PCR 11 when the initrd is about to
transition into the host file system, i.e. when it achieved its
purpose. It is supposed to act as barrier between kernel/initrd
code and host OS code. (This string is extended at stop of
systemd-pcrphase-initrd.service.)
3. "sysinit" is extended into PCR 11 when basic system initialization
is complete (which includes local file systems have been mounted),
and the system begins starting regular system services. (This
string is extended at start of systemd-pcrphase-sysinit.service.)
4. "ready" is extended into PCR 11 during later boot-up, after remote
file systems have been activated (i.e. after remote-fs.target), but
before users are permitted to log in (i.e. before
systemd-user-sessions.service). It is supposed to act as barrier
between the time where unprivileged regular users are still
prohibited to log in and where they are allowed to log in. (This
string is extended at start of systemd-pcrphase.service.)
5. "shutdown" is extended into PCR 11 when system shutdown begins. It
is supposed to act as barrier between the time the system is fully
up and running and where it is about to shut down. (This string is
extended at stop of systemd-pcrphase.service.)
6. "final" is extended into PCR 11 at the end of system shutdown. It
is supposed to act as barrier between the time the service manager
still runs and when it transitions into the final boot phase where
service management is not available anymore. (This string is
extended at stop of systemd-pcrphase-sysinit.service.)
During a regular system lifecycle, the strings "enter-initrd" →
"leave-initrd" → "sysinit" → "ready" → "shutdown" → "final" are
extended into PCR 11, one after the other.
Specific phases of the boot process may be referenced via the series of
strings measured, separated by colons (the "boot path"). For example,
the boot path for the regular system runtime is
"enter-initrd:leave-initrd:sysinit:ready", while the one for the initrd
is just "enter-initrd". The boot path for the the boot phase before the
initrd, is an empty string; because that's hard to pass around a single
colon (":") may be used instead. Note that the aforementioned six
strings are just the default strings and individual systems might
measure other strings at other times, and thus implement different and
more fine-grained boot phases to bind policy to.
By binding policy of TPM2 objects to a specific boot path it is
possible to restrict access to them to specific phases of the boot
process, for example making it impossible to access the root file
system's encryption key after the system transitioned from the initrd
into the host root file system.
Use systemd-measure(1) to pre-calculate expected PCR 11 values for
specific boot phases (via the --phase= switch).
OPTIONS
The /lib/systemd/system-pcrphase executable may also be invoked from
the command line, where it expects the word to extend into PCR 11, as
well as the following switches:
--bank=
Takes the PCR banks to extend the specified word into. If not
specified the tool automatically determines all enabled PCR banks
and measures the word into all of them.
--tpm2-device=PATH
Controls which TPM2 device to use. Expects a device node path
referring to the TPM2 chip (e.g. /dev/tpmrm0). Alternatively the
special value "auto" may be specified, in order to automatically
determine the device node of a suitable TPM2 device (of which there
must be exactly one). The special value "list" may be used to
enumerate all suitable TPM2 devices currently discovered.
--graceful
If no TPM2 firmware, kernel subsystem, kernel driver or device
support is found, exit with exit status 0 (i.e. indicate success).
If this is not specified any attempt to measure without a TPM2
device will cause the invocation to fail.
-h, --help
Print a short help text and exit.
--version
Print a short version string and exit.
SEE ALSO
systemd(1), systemd-stub(7), systemd-measure(1)
systemd 252 SYSTEMD-PCRPHASE.SERVICE(8)
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