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
The man page doesn't even mention errno. It just says that ferror() should
be used to check for errors. Those writes are unlikely to fail, but if they
do, errno might even be 0. Also, we have fflush_and_check() which does
additional paranoia around errno, because we apparently do not trust that
errno will always be set correctly.
We already save it in PEM format, also store it TPM2_PUBLIC format next
to it. This is useful for usage with systemd-cryptenroll's
--tpm2-device-key= switch.
Because most TPM2 functions here are 'library-like' functions, they should be
at debug level, not error level.
The only functions not reduced to logging at debug are tpm2_list_devices(),
since it is expected to print output, and the tpm2_parse_pcr_argument_*()
functions, since the system-wide parse_*_argument() functions generally log at
error level.
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
