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

From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
	Nathan Chancellor <nathan@kernel.org>,
	 Nick Desaulniers <ndesaulniers@google.com>
Cc: Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	 Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	 Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, llvm@lists.linux.dev,
	 linux-kernel@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	 Tadeusz Struk <tadeusz.struk@linaro.org>,
	 syzbot+6cde2282daa792c49ab8@syzkaller.appspotmail.com
Subject: [PATCH v2 5/5] KVM: x86: Bail to userspace if emulation of atomic user access faults
Date: Wed,  2 Feb 2022 00:49:45 +0000	[thread overview]
Message-ID: <20220202004945.2540433-6-seanjc@google.com> (raw)
In-Reply-To: <20220202004945.2540433-1-seanjc@google.com>

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

