[PATCH 4/6] KVM: x86: emulation of dword cmov on long-mode should clear [63:32]

Nadav Amit
2014-06-15T13:13:15Z

Even if the condition of cmov is not satisfied, bits[63:32] should be cleared.
This is clearly stated in Intel's CMOVcc documentation. The solution is to
reassign the destination onto itself if the condition is unsatisfied. For that
matter the original destination value needs to be read.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
---
arch/x86/kvm/emulate.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 0183350..b354531 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3905,7 +3905,7 @@ static const struct opcode twobyte_table[256] = {
N, N,
N, N, N, N, N, N, N, N,
/* 0x40 - 0x4F */
- X16(D(DstReg | SrcMem | ModRM | Mov)),
+ X16(D(DstReg | SrcMem | ModRM)),
/* 0x50 - 0x5F */
N, N, N, N, N, N, N, N, N, N, N, N, N, N, N, N,
/* 0x60 - 0x6F */
@@ -4799,8 +4799,10 @@ twobyte_insn:
ops->get_dr(ctxt, ctxt->modrm_reg, &ctxt->dst.val);
break;
case 0x40 ... 0x4f: /* cmov */
- ctxt->dst.val = ctxt->dst.orig_val = ctxt->src.val;
- if (!test_cc(ctxt->b, ctxt->eflags))
+ if (test_cc(ctxt->b, ctxt->eflags))
+ ctxt->dst.val = ctxt->src.val;
+ else if (ctxt->mode != X86EMUL_MODE_PROT64 ||
+ ctxt->op_bytes != 4)
ctxt->dst.type = OP_NONE; /* no writeback */
break;
case 0x80 ... 0x8f: /* jnz rel, etc*/
--
1.9.1