Re: [PATCH Part2 v5 00/45] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support

Borislav Petkov
2021-11-12T18:35:28Z

On Fri, Nov 12, 2021 at 09:59:46AM -0800, Dave Hansen wrote:
> Or, is there some mechanism that prevent guest-private memory from being
> accessed in random host kernel code?

So I'm currently under the impression that random host->guest accesses
should not happen if not previously agreed upon by both.

Because, as explained on IRC, if host touches a private guest page,
whatever the host does to that page, the next time the guest runs, it'll
get a #VC where it will see that that page doesn't belong to it anymore
and then, out of paranoia, it will simply terminate to protect itself.

So cloud providers should have an interest to prevent such random stray
accesses if they wanna have guests. :)

> This sounds like a _possible_ opportunity for the guest to do some extra
> handling. It's also quite possible that this #VC happens in a place
> that the guest can't handle.

How? It'll get a #VC when it first touches that page.

I'd say the #VC handler should be able to deal with it...

Thx.

--
Regards/Gruss,
Boris.