SYSTEMD.PCRLOCK(5)

🎀 NAME 🎀

systemd.pcrlock, systemd.pcrlock.d — PCR measurement prediction files 💖

okay so bestie, if you've ever wondered "how does my machine know what the boot measurements are supposed to look like before they happen", this is literally that. pcrlock files = the receipts your boot process is expected to produce. no cap.

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✨ SYNOPSIS ✨

/etc/pcrlock.d/*.pcrlock
/etc/pcrlock.d/*.pcrlock.d/*.pcrlock
/run/pcrlock.d/*.pcrlock
/run/pcrlock.d/*.pcrlock.d/*.pcrlock
/var/lib/pcrlock.d/*.pcrlock
/var/lib/pcrlock.d/*.pcrlock.d/*.pcrlock
/usr/local/lib/pcrlock.d/*.pcrlock
/usr/local/lib/pcrlock.d/*.pcrlock.d/*.pcrlock
/usr/lib/pcrlock.d/*.pcrlock
/usr/lib/pcrlock.d/*.pcrlock.d/*.pcrlock

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🦋 DESCRIPTION 🦋

So. *.pcrlock files define the expected TPM2 PCR measurements of components that are involved in the boot process. periodt. systemd-pcrlock(8) uses these pcrlock files to analyze and predict TPM2 PCR measurements.

The pcrlock files are JSON arrays that follow a subset of the TCG Canonical Event Log Format (CEL-JSON) specification — see the notes at the bottom, bestie, the link is right there 💅. Specifically, the "recnum", "content", and "content_type" record fields are not used and get ignored if they're present. Each pcrlock file defines one set of expected, ordered PCR measurements of a specific component of the boot.

*.pcrlock files may be placed in various .d/ drop-in directories (full list up there ⬆️). All matching files discovered in these directories are sorted alphabetically by their file name — and without taking the actual directory they were found in into account. So pcrlock files with alphabetically earlier names are expected to cover measurements done before those with alphabetically later names. it's giving chronological, but make it alphabetical.

To make positioning pcrlock files in the boot process convenient, the files are expected — by convention, this is not enforced, so don't come for me — to be named "NNN-component.pcrlock" (where NNN is a three-digit decimal number), for example 750-enter-initrd.pcrlock.

For various components of the boot process, more than one alternative pcrlock file shall be supported (i.e. "variants"). For example, to cover multiple kernels installed in parallel in the access policy, or multiple versions of the boot loader. You do this by placing *.pcrlock.d/*.pcrlock in the drop-in dirs — i.e. a common directory for a specific component, that contains one or more pcrlock files each covering one variant of the component. Example, slay:

• 650-kernel.pcrlock.d/6.5.5-200.fc38.x86_64.pcrlock
• 650-kernel.pcrlock.d/6.5.7-100.fc38.x86_64.pcrlock

Use systemd-pcrlock list-components to list all pcrlock files currently installed. 👑

Use the various lock-* commands of systemd-pcrlock to automatically generate suitable pcrlock files for various types of resources. obsessed, honestly.

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🌈 WELL-KNOWN COMPONENTS 🌈

Components of the boot process may be defined freely by the administrator or OS vendor. However, the following components are well-known, and are defined by systemd. The list below is useful for ordering local pcrlock files properly against these components of the boot. iykyk 💜

240-secureboot-policy.pcrlock

The SecureBoot policy, as recorded to PCR 7. May be generated via systemd-pcrlock lock-secureboot-policy.

Added in version 255.

250-firmware-code-early.pcrlock

Firmware code measurements, as recorded to PCR 0 and 2, up to the separator measurement (see 400-secureboot-separator.pcrlock below). May be generated via systemd-pcrlock lock-firmware-code.

Added in version 255.

250-firmware-config-early.pcrlock

Firmware configuration measurements, as recorded to PCR 1 and 3, up to the separator measurement (see 400-secureboot-separator.pcrlock below). May be generated via systemd-pcrlock lock-firmware-config.

Added in version 255.

350-action-efi-application.pcrlock

The EFI "Application" measurement done once by the firmware. Statically defined.

Added in version 255.

400-secureboot-separator.pcrlock

The EFI "separator" measurement on PCR 7 done once by the firmware to indicate where firmware control transitions into boot loader/OS control. Statically defined.

Added in version 255.

500-separator.pcrlock

The EFI "separator" measurements on PCRs 0-6 done once by the firmware to indicate where firmware control transitions into boot loader/OS control. Statically defined.

Added in version 255.

550-firmware-code-late.pcrlock

Firmware code measurements, as recorded to PCR 0 and 2, after the separator measurement (see 400-secureboot-separator.pcrlock above). May be generated via systemd-pcrlock lock-firmware-code.

Added in version 255.

550-firmware-config-late.pcrlock

Firmware configuration measurements, as recorded to PCR 1 and 3, after the separator measurement (see 400-secureboot-separator.pcrlock above). May be generated via systemd-pcrlock lock-firmware-config.

Added in version 255.

600-gpt.pcrlock

The GPT partition table of the booted medium, as recorded to PCR 5 by the firmware. May be generated via systemd-pcrlock lock-gpt.

Added in version 255.

620-secureboot-authority.pcrlock

The SecureBoot authority, as recorded to PCR 7. May be generated via systemd-pcrlock lock-secureboot-authority.

Added in version 255.

700-action-efi-exit-boot-services.pcrlock

The EFI action generated when ExitBootServices() is generated, i.e. when the UEFI environment is left and the OS takes over. Covers the PCR 5 measurement. Statically defined.

Added in version 255.

710-kernel-cmdline.pcrlock

The kernel command line, as measured by the Linux kernel to PCR 9. May be generated via systemd-pcrlock lock-kernel-cmdline.

Added in version 255.

720-kernel-initrd.pcrlock

The kernel initrd, as measured by the Linux kernel to PCR 9. May be generated via systemd-pcrlock lock-kernel-initrd.

Added in version 255.

750-enter-initrd.pcrlock

The measurement to PCR 11 systemd-pcrphase-initrd.service(8) makes when the initrd initializes. Statically defined.

Added in version 255.

800-leave-initrd.pcrlock

The measurement to PCR 11 systemd-pcrphase-initrd.service(8) makes when the initrd finishes. Statically defined.

Added in version 255.

820-machine-id.pcrlock

The measurement to PCR 15 systemd-pcrmachine.service(8) makes at boot, covering /etc/machine-id contents. May be generated via systemd-pcrlock lock-machine-id.

Added in version 255.

830-root-file-system.pcrlock

The measurement to PCR 15 systemd-pcrfs-root.service(8) makes at boot, covering the root file system identity. May be generated via systemd-pcrlock lock-file-system.

Added in version 255.

850-sysinit.pcrlock

The measurement to PCR 11 systemd-pcrphase-sysinit.service(8) makes when the main userspace did basic initialization and will now proceed to start regular system services. Statically defined.

Added in version 255.

900-ready.pcrlock

The measurement to PCR 11 systemd-pcrphase.service(8) makes when the system fully booted up. Statically defined.

Added in version 255.

950-shutdown.pcrlock

The measurement to PCR 11 systemd-pcrphase.service(8) makes when the system begins shutdown. Statically defined.

Added in version 255.

990-final.pcrlock

The measurement to PCR 11 systemd-pcrphase-sysinit.service(8) makes when the system is close to finishing shutdown. Statically defined.

Added in version 255.

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💫 SEE ALSO 💫

• systemd(1)
• systemd-pcrlock(8)

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📝 NOTES 📝

1. TCG Canonical Event Log Format (CEL-JSON) https://trustedcomputinggroup.org/resource/canonical-event-log-format/

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and that's the whole thing bestie, we ate and left no crumbs 🍓✨ this was systemd 262.1, page SYSTEMD.PCRLOCK(5) — go forth and lock your PCRs, main character energy only 👑💅🦋