Messages in this thread | | | Date | Thu, 21 Oct 2021 20:46:30 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v6 08/42] x86/sev-es: initialize sev_status/features within #VC handler |
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On Thu, Oct 21, 2021 at 06:47:50PM +0100, Dr. David Alan Gilbert wrote: > Hang on, I think it's perfectly fine for it to clear that bit - it just > gets caught if it *sets* it (i.e. claims to be a chip unaffected by the > bug). > > i.e. if guestval=0 then (GustVal & whatever) == GuestVal > fine > > ?
Bah, ofc. The name of the bit is NullSelectorClearsBase - so when it is clear, we will note we're affected, as that patch does:
+ /* + * CPUID bit above wasn't set. If this kernel is still running + * as a HV guest, then the HV has decided not to advertize + * that CPUID bit for whatever reason. For example, one + * member of the migration pool might be vulnerable. Which + * means, the bug is present: set the BUG flag and return. + */ + if (cpu_has(c, X86_FEATURE_HYPERVISOR)) { + set_cpu_bug(c, X86_BUG_NULL_SEG); + return; + }
I have managed to flip the meaning in my mind.
Ok, that makes more sense.
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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