5 ms·
That depends on which PCRs you bind your TPM-backend encryption key to. See this list: https://uapi-group.org/specifications/specs/linux_tpm_pcr_registry/ https
by gameoverhumans 3y ago
That depends on which PCRs you bind your TPM-backend encryption key to. See this list: https://uapi-group.org/specifications/specs/linux_tpm_pcr_registry/ https://uapi-group.org/specifications/specs/linux_tpm_pcr_re...
As an example, Arch Wiki encourages you to bind to PCR 0+7: https://wiki.archlinux.org/title/Trusted_Platform_Module#systemd-cryptenroll https://wiki.archlinux.org/title/Trusted_Platform_Module#sys... ... both of those are firmware-level PCRs, not OS ones.
- tomatocracy 3y agoPCRs 0+7 might not be sufficient if you don't have an up to date dbx (revocation list) - older versions of shim won't (I think) extend into PCR 7 enough information on what they chainload. This means a malicious bootloader could fake the correct PCR extensions. Updating dbx to a version which revokes versions of shim with this issue would fix this I think, as would including PCR 4 in the list bound to, to make doubly sure that the version of shim is new enough not to present a risk.