linux-kernel - [PATCH 5.15 1/2] KVM: x86: Bail to userspace if emulation of atomic user access faults

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Date: Thu,  4 Apr 2024 16:40:03 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: stable@...r.kernel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	David Matlack <dmatlack@...gle.com>, Pasha Tatashin <tatashin@...gle.com>, 
	Michael Krebs <mkrebs@...gle.com>, Jim Mattson <jmattson@...gle.com>
Subject: [PATCH 5.15 1/2] KVM: x86: Bail to userspace if emulation of atomic
 user access faults

Upstream commit 5d6c7de6446e9ab3fb41d6f7d82770e50998f3de.

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@...gle.com>
Message-Id: <20220202004945.2540433-6-seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.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 aa6f700f8c5f..a9c26397dcfd 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7105,7 +7105,7 @@ 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;
 
-- 
2.44.0.478.gd926399ef9-goog