Messages in this thread | | | Date | Thu, 12 Jan 2023 10:36:39 -0800 | Subject | Re: [PATCH 3/7] x86/cpu: Disable kernel LASS when patching kernel alternatives | From | "Chen, Yian" <> |
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On 1/11/2023 4:37 PM, Dave Hansen wrote: > On 1/11/23 16:27, Chen, Yian wrote: >>> 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"? >>> >> Yes, I tested with clearcpuid=smap. > It works by accident, then. > > clearcpuid=smap means that the kernel should be running as if > CPUID.(EAX=07H,ECX=0H):EBX.SMAP[bit 20]==0. STAC/CLAC should #UD in > that case. > It could be something wrong in my Simics simulation environment.
> The only reason that it happens to work is that STAC/CLAC apparently > actually continue to work even if CR4.SMAP==0. > > I'm actually a _bit_ surprised by this, but I bet there's a good reason > for it. > > In any case, please just make LASS dependent on SMAP. It's the right > thing to do on several levels. Sure, I will add the dependency.
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