Re: Enrolling PCR11 does not work as expected

[Lennart Poettering <lennart@xxxxxxxxxxxxxx>]

On Mi, 05.07.23 08:30, Felix Rubio (felix@xxxxxxxxx) wrote:

> Hi everybody,
>
> In my setup (sd-boot+UKI+LUKS) I am using PCRs 7+11+14 to unlock the LUKS
> drive. Should I use only PCRs 7+14 everything works, but when I add 11 I
> need to provide the rescue password every single time I boot.
>
> I have extracted the values of those PCRs using tpm2_pcrread in two
> consecutive boots, and they are equal, so at least the issue is
> reproducible.
>
> To enroll the PCRs, after a new kernel (and, therefore, the UKI) has been
> generated, I run the following command:
>
> systemd-cryptenroll --wipe-slot=tpm2 --tpm2-device=auto --tpm2-pcrs=7+11+14
> <device>
>
> After reading the documentation on systemd-measure (that I am not using at
> the moment): could it be that there are events added to PCR 11 after the
> unlocking has happened, so that I am enrolling the wrong PCR value?
> Otherwise... what am I doing wrong?

We mesaure the "boot phase" into PCR 11 too. See
systemd-pcrphase.service(8) for details.

Generally the assumption is that PCR 11 is used for signed PCR
policies, i.e. under vendor control.

Lennart

--
Lennart Poettering, Berlin