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

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Date:   Wed,  2 Feb 2022 00:49:45 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        llvm@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Tadeusz Struk <tadeusz.struk@...aro.org>,
        syzbot+6cde2282daa792c49ab8@...kaller.appspotmail.com
Subject: [PATCH v2 5/5] KVM: x86: Bail to userspace if emulation of atomic
 user access faults

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>
---
 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