Messages in this thread | | | From | Jim Mattson <> | Date | Wed, 16 Aug 2023 15:37:20 -0700 | Subject | Re: [PATCH 1/2] x86/microcode/AMD: Load late on both threads too |
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On Wed, Aug 16, 2023 at 2:59 PM Borislav Petkov <bp@alien8.de> wrote: > > On Wed, Aug 16, 2023 at 02:36:57PM -0700, Jim Mattson wrote: > > Doesn't this render that attestation misleading, since the microcode > > patch may not have been loaded on all logical processors? > > For that it doesn't matter because the microcode engine is shared > between the two threads. The updated microcode revision is shown on any > of the two threads so you can load on one only. And we did this for > years. > > Only recently we started loading on both and we will be doing that from > now on.
SEV-SNP is supposed to protect the guest from a malicious host. A malicious host may not load the microcode update on both threads. As a result, it gives me some concern when I see something like this (https://lore.kernel.org/lkml/20230808190239.131508-1-john.allen@amd.com/):
+NOTE: For Genoa (Family=0x19 Model=0x11) and Bergamo (Family=0x19 Model=0xa0), +either AGESA version >= 1.0.0.8 OR a kernel with the following commit is +required: +a32b0f0db3f3 ("x86/microcode/AMD: Load late on both threads too")
It seems problematic if the guest can't tell from the attestation whether or not the identified microcode revision has been correctly applied.
> What could be problematic is if it simply fails loading on some cores > - regardless of SMT - but that would be problematic not only to SEV-SNP > attestation but to the general system health. tglx has some patches > which verify what has been successfully loaded where so hopefully we'll > be verifying more in that area.
I had assumed that the SEV-SNP microcode revision attestation was for all logical processors on the host. Are you saying that it is not?
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