Messages in this thread Patch in this message | | | Date | Tue, 10 Jan 2023 14:41:25 -0800 | Subject | Re: [PATCH 3/7] x86/cpu: Disable kernel LASS when patching kernel alternatives | From | Sohil Mehta <> |
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On 1/9/2023 9:52 PM, Yian Chen wrote:
> LASS stops access to a lower half address in kernel, > and this can be deactivated if AC bit in EFLAGS > register is set. Hence use stac and clac instructions > around access to the address to avoid triggering a > LASS #GP fault. >
It seems we are implicitly relying on the on stac() and clac() calls that are added for SMAP. Have you tried running with SMAP disabled i.e "clearcpuid=smap"?
I believe there needs to be a dependency between LASS and SMAP.
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c index d95221117129..00bc7e4a65d2 100644 --- a/arch/x86/kernel/cpu/cpuid-deps.c +++ b/arch/x86/kernel/cpu/cpuid-deps.c @@ -79,6 +79,7 @@ static const struct cpuid_dep cpuid_deps[] = { { X86_FEATURE_XFD, X86_FEATURE_XSAVES }, { X86_FEATURE_XFD, X86_FEATURE_XGETBV1 }, { X86_FEATURE_AMX_TILE, X86_FEATURE_XFD }, + { X86_FEATURE_LASS, X86_FEATURE_SMAP }, {} };
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