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Joerg Roedel authored
In kernels compiled with CONFIG_PARAVIRT=n, the compiler re-orders the DR7 read in exc_nmi() to happen before the call to sev_es_ist_enter(). This is problematic when running as an SEV-ES guest because in this environment the DR7 read might cause a #VC exception, and taking #VC exceptions is not safe in exc_nmi() before sev_es_ist_enter() has run. The result is stack recursion if the NMI was caused on the #VC IST stack, because a subsequent #VC exception in the NMI handler will overwrite the stack frame of the interrupted #VC handler. As there are no compiler barriers affecting the ordering of DR7 reads/writes, make the accesses to this register volatile, forbidding the compiler to re-order them. [ bp: Massage text, make them volatile too, to make sure some aggressive compiler optimization pass doesn't discard them. ] Fixes: 315562c9 ("x86/sev-es: Adjust #VC IST Stack on entering NMI handler") Reported-by:
Alexey Kardashevskiy <aik@amd.com> Signed-off-by:
Joerg Roedel <jroedel@suse.de> Signed-off-by:
Borislav Petkov (AMD) <bp@alien8.de> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20230127035616.508966-1-aik@amd.com
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