Re: [PATCH v2 2/7] x86/boot: Delay sev_verify_cbit() a bit

Borislav Petkov
2023-01-19T13:19:26Z

On Mon, Jan 16, 2023 at 03:25:35PM +0100, Peter Zijlstra wrote:
> Per the comment it is important to call sev_verify_cbit() before the
> first RET instruction, this means we can delay calling this until more

Make that "... this means that this can be delayed until... "

And I believe this is not about the first RET insn but about the *next* RET
which will pop poisoned crap from the unencrypted stack and do shits with it.

Also, there's this over sev_verify_cbit():

* sev_verify_cbit() is called before switching to a new long-mode page-table
* at boot.

so you can't move it under the

movq %rax, %cr3

Looking at this more, there's a sme_enable() call on the BSP which is already in
C.

So, can we do that C-bit verification once on the BSP, *in C* which would be a
lot easier, and be done with it?

Once it is verified there, the bit is the same on all APs so all good.

Right?

joro?

--
Regards/Gruss,
Boris.