[systemd-devel] systemd-cryptenroll with TPM2

[Aleksandar Kostadinov]

Hello,

This is more of a user question but I didn't find any other suitable forum
to ask.

I want to install a server that should have an encrypted root but be able
to reboot unattended.

systemd-cryptenroll with TPM2 looks like a viable option. I'm concerned
about which PCRs to pin so that an average attacker  won't be able to
decrypt the volume having physical possession of the server. This means I'm
not concerned about cracking the TPM chip or reading out life memory.

To me it is acceptable to pin a lot of them so that adding/changing devices
would prevent automatic decryption. Also 5 looks good about changed GPT
partitions.

I'm concerned though about an attacker replacing the encrypted root volume
with a non-encrypted one. Which may result in system booting an attacker
controlled environment while PCRs may be in a state that allows decryption
of the original root volume.

Would anything prevent the system from booting with a replaced root volume?

If it can boot in such a way, which PCRs need to be pinned to remove the
ability to decrypt the original root volume?

If there is presently no such PCR, can some custom validation be added in
the process to take care of that?

Thank you!
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