GRUB and all other boot loaders are unecessary with UEFI. See my comment history for more.
Kernel updates + Secure Boot is easy with a Debian hook.
The hard part is making it work with TPM when you want to add encryption...
Say that you have disabled usb booting and secured UEFI settings with a password. If you extract the cpu (and thereby its tpm) and the disk, then you'd still be able to boot, right? Meaning that without a TPM pin, you'd be able to do OP's attack on a different motherboard even when the original machine was off and UEFI settings secured.
What am I missing? Is it that easy to circumvent UEFI settings protection and maintain the PCR 7 value?
[1] https://blog.scrt.ch/2023/09/15/a-deep-dive-into-tpm-based-b...
So I really doubt TPM will release the keys on a different motherboard with different UEFI settings.
User changed motherboard and TPM complains: https://old.reddit.com/r/pcmasterrace/comments/vdvni1/swappe...
> PCR 7 changes when UEFI SecureBoot mode is enabled/disabled, or firmware certificates (PK, KEK, db, dbx, …) are updated. The shim project will measure most of its (non-MOK) certificates and SBAT data into this PCR. — https://uapi-group.org/specifications/specs/linux_tpm_pcr_re...
It makes sense to use the certificates to generate PCR 7. I wonder if you can swap out the motherboard with one of the same model with the same certificates without modifying the PCR 7 digest...
But if Shim actually modifies the digest, I guess that SB would completely mitigate OP's exploit since the TPM policy is going to fail when the PCR 7 values doesn't match.