alt Hacker NewsOn my system, I used `tpm2-measure-pcr=yes` in `/etc/crypttab.initramfs`, then used `--tpm2-pcrs=0+2+7+15:sha256=0000000000000000000000000000000000000000000000000000000000000000` with `systemd-cryptenroll`.
As soon as a volume is decrypted, initrd will write `volume-key` to PCR 15, so any further executables can no longer access the data stored in the TPM.
Replies
oddlama • 01/17/2025
This is great if you only have a single disk, but if you have multiple encrypted disks that are unlocked in the initrd this way, then if you can gain control flow by faking data on the last decrypted disk you can still gain access to all the previously unlocked partitions.
Of course you cannot unseal the secret from the TPM anymore.
➕ show 3 replies
Yes, that seems a good extra level of defense. Allow unsealing only once. We extend a PCR with random data.