[systemd-devel] Is tpm2-measure-pcr really an additional security?

[Diorcet Yann]

Le 10/03/2025 à 21:42, aplanas a écrit :
> On 2025-03-10 18:25, Diorcet Yann wrote:
>> Le 10/03/2025 à 17:27, Adrian Vovk a écrit :
>
>> 2) Just before opening the var LUKS:
>>
>> PCR15=0 or something predictable
>>
>> cryptsetup is used to open var and update PCR15 thanks to
>> tpm2-measure-pcr=yes. but in this case /dev/sda1 is replaced with the
>> original /dev/sda1 partition.
>
> I think that you mean that /dev/sda2 (/var) is replaced with the 
> original /dev/sda1 (rootfs), so mounting the original root in /var, 
> right?
Yes that it, sorry for the mistake.
>
>> PCR15=hash1
>>
>> 3) initrd makes the mount of the fs, makes multiple measurements
>> (notably on PCR11 with leave-initrd) then chroots and executes
>> malicious init.
>>
>>
>> Is PCR15 checked against a pre-calculated value saved in the signed
>> initrd before leaving initrd? If it's not the case, then when
>> executing the init from the chrooted malicious partition, the original
>> /dev/sda1 LUKS will be opened and mounted as var.
>
> You need a service in the initrd to do that.  systemd AFAIK is not 
> currently providing one, but the plumbing is there to bring your own.

Thanks for the links btw

Regards,

Yann