Re: [PATCH 2/3] x86/cpu/amd: Add feature bit for MSR_AMD64_LS_CFG enumeration
From: Borislav Petkov
Date: Wed Nov 09 2022 - 13:35:09 EST
On Wed, Nov 09, 2022 at 09:37:20AM -0800, Pawan Gupta wrote:
> Looks like we need to restore this MSR too,
Why do we? Is that MSR read-only too or what is the reason for that one?
> and we can use existing X86_FEATURE_XMM2 to enumerate it.
Or 86_FEATURE_LFENCE_RDTSC.
> If SSBD is the only reason to restore MSR_AMD64_LS_CFG then we should
> be able to use X86_FEATURE_LS_CFG_SSBD for enumeration.
Yes, MSR_AMD64_LS_CFG is used in SSBD mitigations. For everything <= 0x12:
/* AMD Family 0xf - 0x12 */
VULNWL_AMD(0x0f, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO),
VULNWL_AMD(0x10, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO),
VULNWL_AMD(0x11, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO),
VULNWL_AMD(0x12, NO_MELTDOWN | NO_SSB | NO_L1TF | NO_MDS | NO_SWAPGS | NO_ITLB_MULTIHIT | NO_MMIO),
On F14h it says here:
[ 0.278930] Speculative Store Bypass: Vulnerable
simply because it is not present there.
--
Regards/Gruss,
Boris.
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