linux-kernel - [PATCH] KVM: X86: Remove stale values from ctxt->memop before emulation

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Date:	Fri, 4 May 2012 18:14:16 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>
CC:	<kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Joerg Roedel <joerg.roedel@....com>
Subject: [PATCH] KVM: X86: Remove stale values from ctxt->memop before emulation

When instruction decoding begins there could be stale values
in the ctxt->memop structure. This causes problems when an
instruction is emulated with more op-bytes then the guest
wants (like the bsr instruction which is always emulated
with 4 or 8 op-bytes).

The stale value in this structure causes the unit-test for
the bsrw instruction to fail. Initialize the memop.val with
0 to prevent such bugs (an alternative fix could be to
always emulate instructions with the number of op-bytes
requested by the guest).

Signed-off-by: Joerg Roedel <joerg.roedel@....com>
---
 arch/x86/kvm/emulate.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index d4bf50c..1b516ec 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3937,6 +3937,7 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
 	struct opcode opcode;

 	ctxt->memop.type = OP_NONE;
+	ctxt->memop.val  = 0;
 	ctxt->memopp = NULL;
 	ctxt->_eip = ctxt->eip;
 	ctxt->fetch.start = ctxt->_eip;
-- 
1.7.9.5

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