Right now systemd-tpm2-setup-early and systemd-pcrphase-initrd.service
are not ordered against each other. However, they require the same slow
resource to operate: the TPM2. If we allow them to access the device
simultaneously, the kernel resource manager like has to save/restore TPM
state while they operate, slowing things down further.
hence, let's avoid all this mess, and just order them against each other
so that the shared resource is first used in full by one and then by the
other.
I opted to order systemd-pcrphase-initrd before
systemd-tpm2-setup-early, since there's value in having the former as
early as possible in userspace, to be a good marker for the transition
from kernel to first userspace. I can see no benefit in the opposite
order however.
Currently the associated units fail if full tpm support is not available
on the system. Similar to systemd-pcrextend, let's add a --graceful option
that exits gracefully if no full TPM support is detected and use it in both
units.
I was looking at the logs in some bug and saw this:
Mar 13 15:55:12 fedora systemd[1]: systemd-pcrmachine.service - TPM2 PCR Machine ID Measurement was skipped because of an unmet condition check (ConditionSecurity=measured-uki).
Mar 13 15:55:12 fedora systemd[1]: Starting systemd-remount-fs.service - Remount Root and Kernel File Systems...
Mar 13 15:55:12 fedora systemd[1]: systemd-tpm2-setup-early.service - TPM2 SRK Setup (Early) was skipped because of an unmet condition check (ConditionSecurity=measured-uki).
This is overly technical, for most units we don't provide this level of
detail about the implementation. So retitle the units to be more accessible.
Also, the fact that it's a v. 2 of the TPM is not that important. We don't
support TPM 1.2, but computers without TPM v2 are getting rare. For other
units we don't advertise the version of hardware, and let's not do this here,
to reduce some complexity.
Distributions apparently only compile a subset of TPM2 drivers into the
kernel. For those not compiled it but provided as kmod we need a
synchronization point: we must wait before the first TPM2 interaction
until the driver is available and accessible.
This adds a tpm2.target unit as such a synchronization point. It's
ordered after /dev/tpmrm0, and is pulled in by a generator whenever we
detect that the kernel reported a TPM2 to exist but we have no device
for it yet.
This should solve the issue, but might create problems: if there are TPM
devices supported by firmware that we don't have Linux drivers for we'll
hang for a bit. Hence let's add a kernel cmdline switch to disable (or
alternatively force) this logic.
Fixes: #30164
This adds an explicit service for initializing the TPM2 SRK. This is
implicitly also done by systemd-cryptsetup, hence strictly speaking
redundant, but doing this early has the benefit that we can parallelize
this in a nicer way. This also write a copy of the SRK public key in PEM
format to /run/ + /var/lib/, thus pinning the disk image to the TPM.
Making the SRK public key is also useful for allowing easy offline
encryption for a specific TPM.
Sooner or later we should probably grow what this service does, the
above is just the first step. For example, the service should probably
offer the ability to reset the TPM (clear the owner hierarchy?) on a
factory reset, if such a policy is needed. And we might want to install
some default AK (?).
Fixes: #27986
Also see: #22637
