linux-kernel - [PATCH] KVM: x86: Avoid emulating instructions on #UD mistakenly

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Message-Id: <1407937813-1461-1-git-send-email-namit@cs.technion.ac.il>
Date:	Wed, 13 Aug 2014 16:50:13 +0300
From:	Nadav Amit <namit@...technion.ac.il>
To:	pbonzini@...hat.com
Cc:	gleb@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Nadav Amit <namit@...technion.ac.il>
Subject: [PATCH] KVM: x86: Avoid emulating instructions on #UD mistakenly

Commit d40a6898e5 mistakenly caused instructions which are not marked as
EmulateOnUD to be emulated upon #UD exception. The commit caused the check of
whether the instruction flags include EmulateOnUD to never be evaluated. As a
result instructions whose emulation is broken may be emulated.  This fix moves
the evaluation of EmulateOnUD so it would be evaluated.

Signed-off-by: Nadav Amit <namit@...technion.ac.il>
---
 arch/x86/kvm/emulate.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 56657b0..37a83b2 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4394,6 +4394,9 @@ done_prefixes:
 
 	ctxt->execute = opcode.u.execute;
 
+	if (!(ctxt->d & EmulateOnUD) && ctxt->ud)
+		return EMULATION_FAILED;
+
 	if (unlikely(ctxt->d &
 		     (NotImpl|EmulateOnUD|Stack|Op3264|Sse|Mmx|Intercept|CheckPerm))) {
 		/*
@@ -4406,9 +4409,6 @@ done_prefixes:
 		if (ctxt->d & NotImpl)
 			return EMULATION_FAILED;
 
-		if (!(ctxt->d & EmulateOnUD) && ctxt->ud)
-			return EMULATION_FAILED;
-
 		if (mode == X86EMUL_MODE_PROT64 && (ctxt->d & Stack))
 			ctxt->op_bytes = 8;
 
-- 
1.9.1

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