linux-kernel - [PATCH 5/5] KVM: x86: Fix wrong masking on relative jump/call

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Date:	Wed,  7 May 2014 15:32:52 +0300
From:	Nadav Amit <namit@...technion.ac.il>
To:	mtosatti@...hat.com, pbonzini@...hat.com, hpa@...or.com
Cc:	gleb@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Nadav Amit <namit@...technion.ac.il>
Subject: [PATCH 5/5] KVM: x86: Fix wrong masking on relative jump/call

Relative jumps and calls do the masking according to the operand size, and not
according to the address size as the KVM emulator does today.  In 64-bit mode,
the resulting RIP is always 64-bit. Otherwise it is masked according to the
instruction operand-size. Note that when 16-bit address size is used, bits
63:32 are unmodified.

Signed-off-by: Nadav Amit <namit@...technion.ac.il>
---
 arch/x86/kvm/emulate.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 6833b41..e406705 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -506,7 +506,9 @@ static void rsp_increment(struct x86_emulate_ctxt *ctxt, int inc)
 
 static inline void jmp_rel(struct x86_emulate_ctxt *ctxt, int rel)
 {
-	register_address_increment(ctxt, &ctxt->_eip, rel);
+	/* 64-bit mode relative jumps are always 64-bit; otherwise mask */
+	int op_bytes = ctxt->mode == X86EMUL_MODE_PROT64 ? 8 : ctxt->op_bytes;
+	masked_increment(&ctxt->eip, op_bytes, rel);
 }
 
 static u32 desc_limit_scaled(struct desc_struct *desc)
-- 
1.9.1

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