[joerichey]

I looked into this on my motherboard, and the issue is that MSI's firmware measures in the TPM events saying "Secure Boot is On", even when it is in this insecure mode.

This means that even if Windows "checks" (via measured boot) that Secure Boot is on, they are still being lied to by the motherboard firmware.

[mjg59]

PCR 7 doesn't just indicate whether secure boot was enabled, it also contains information about which certificates were used to boot. Obviously if you'll happily sign something unsigned the unsigned thing can just fake a measurement that contains the expected certificate, but I'd be interested to see what the event log looks like on one of these systems when it boots an unsigned binary.