Messages in this thread Patch in this message | | | Date | Sat, 28 Jan 2023 22:24:56 +1100 | Subject | Re: [Question PATCH kernel] x86/amd/sev/nmi+vc: Fix stack handling (why is this happening?) | From | Alexey Kardashevskiy <> |
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On 28/1/23 04:25, Joerg Roedel wrote: > On Fri, Jan 27, 2023 at 10:56:26PM +1100, Alexey Kardashevskiy wrote: >> https://github.com/aik/linux/commit/d0d6bbb58fcd927ddd1f8e9d42ab121920c7eafc > > Okay, I reproduced the problem here and the root cause turned out to be > that the compiler moved the DR7 read instruction before the 5-byte NOP > which becomes the call to sev_es_ist_enter() in SEV-ES guests. This is > guaranteed to cause #VC exception stack recursion if the NMI was > triggered on the #VC stack, and that leads to all kinds of undefined > behavior.
Cool!
(out of curiosity) where do you see these NOPs? "objdump -D vmlinux" does not show any, is this after lifepatching?
Meanwhile, this seems to be doing the right thing:
diff --git a/arch/x86/include/asm/debugreg.h b/arch/x86/include/asm/debugreg.h index b049d950612f..687b15297057 100644 --- a/arch/x86/include/asm/debugreg.h +++ b/arch/x86/include/asm/debugreg.h @@ -39,7 +39,7 @@ static __always_inline unsigned long native_get_debugreg(int regno) asm("mov %%db6, %0" :"=r" (val)); break; case 7: - asm("mov %%db7, %0" :"=r" (val)); + asm volatile ("mov %%db7, %0" :"=r" (val));
-- Alexey
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