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On Thu, 2021-01-07 at 11:50 +0100, Laszlo Ersek wrote:
> (Adding James, David, Daniel)

Thanks.  I'm missing a lot of context, so I'll try to answer the SEV
case only.  Except I will remark that if you boot without a separate
vars and code OVMF, then you need the combined OVMF.fd which contains a
non modifiable initial variable store

[...] 
> Now, with SEV, Secure Boot gains *further* usefulness, but relatedly,
> it faces a new problem as well. Above, I mention "option ROM
> verification".

Actually, I'm not sure about this; I don't believe secure boot adds any
real value and it introduces a problem: the current proposal has the
grub component verified by hash and the kernel verified by being on the
encrypted partition so there's no real additional security secure boot
can provide.  The problem is that if you provide the vars fd, it
doesn't get attested, so effectively its a licence for the host owner
to muck with your OVMF configuration which also isn't good for security
and finally, as you discus below, SEV doesn't use SMI which means the
vars fd doesn't operate safely.

James