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NEWS: expand on systemd-measure a bit

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Lennart Poettering 2022-10-12 10:33:47 +02:00
parent 4d727f8686
commit 25d615eb70
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NEWS
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@ -39,21 +39,35 @@ CHANGES WITH 252 in spe:
New Features:
* systemd-measure is a new tool to precalculate and sign expected TPM2
PCR values if a given unified kernel image (UKI) with systemd-stub is
booted. This is useful for implementing TPM2 policies on LUKS volumes
and encrypted system/service credentials, that bind robustly to a
kernel carrying such signature information. The signed expected PCR
information can be embedded inside the UKI image for this purpose so
that it is automatically available for userspace once booted.
systemd-cryptsetup and systemd-creds have been updated to make use of
this information if available in the booted kernel. Net effect: if
you boot a properly prepared kernel, disk encryption now defaults to
be locked to kernels which carry PCR signatures from the same
keypair, i.e.: if a hypothetical distro FooOS would prepare a kernel
like this, disk encryption can be naturally bound to only FooOS
kernels, and not be unlockable on other kernels. (This is optional,
and only done in case the kernel *is* prepared like that).
* systemd-measure is a new tool for precalculating and signing expected
TPM2 PCR values seen once a given unified kernel image (UKI) with
systemd-stub is booted. This is useful for implementing TPM2 policies
for LUKS encrypted volumes and encrypted system/service credentials,
that robustly bind to kernels carrying appropriate PCR signature
information. The signed expected PCR information may be embedded
inside UKI images for this purpose so that it is automatically
available in userspace, once the UKI is booted.
systemd-cryptsetup, systemd-cryptenroll and systemd-creds have been
updated to make use of this information if available in the booted
kernel.
Net effect: if you boot a properly prepared kernel, TPM-bound disk
encryption now defaults to be locked to kernels which carry PCR
signatures from the same signature key pair. Example: if a
hypothetical distro FooOS prepares its UKI kernels like this,
TPM-based disk encryption is now – by default – bound to only FooOS
kernels, and encrypted volumes bound to the TPM cannot be unlocked on
other kernels from other sources. (But do note this behaviour
requires preparation/enabling in the UKI, and of course users can
always enroll non-TPM ways to unlock the volume.)
Binding TPM-based disk encryption to public keys/signatures of PCR
values — instead of literal PCR values — addresses the inherent
"brittleness" of traditional PCR-bound TPM disk encryption schemes:
disks remain accessible even if the UKI image is updated, without any
prepartion during the update scheme — as long as each UKI carries the
necessary PCR signature information.
* systemd-pcrphase is a new tool that is invoked at 4 places during
system runtime, and measures additional words into TPM2 PCR 11, to