[PATCH v2 5/5] KVM: x86: Bail to userspace if emulation of atomic user access faults

Sean Christopherson
2022-02-02T00:50:14Z

Exit to userspace when emulating an atomic guest access if the CMPXCHG on
the userspace address faults. Emulating the access as a write and thus
likely treating it as emulated MMIO is wrong, as KVM has already
confirmed there is a valid, writable memslot.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/x86.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c9cac3100f77..24e0981816c0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7217,7 +7217,7 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
}

if (r < 0)
- goto emul_write;
+ return X86EMUL_UNHANDLEABLE;
if (r)
return X86EMUL_CMPXCHG_FAILED;

--
2.35.0.rc2.247.g8bbb082509-goog