[PATCHv3] KVM: x86 emulator: fix BitOp instruction emulation

[Wei Yongjun <yjwei@xxxxxxxxxxxxxx>]

If bit offset operands is a negative number, BitOp instruction
will return wrong value. This patch fix it.

Signed-off-by: Wei Yongjun <yjwei@xxxxxxxxxxxxxx>
---
 arch/x86/kvm/emulate.c |   45 ++++++++++++++++++++++++++++++---------------
 1 files changed, 30 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index d197b46..8763708 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -724,6 +724,33 @@ done:
 	return rc;
 }
 
+static void fetch_bit_operand(struct decode_cache *c)
+{
+	unsigned long mask, byte_offset;
+
+	if (c->dst.type != OP_MEM || c->src.type != OP_REG) {
+		/* Only subword offset */
+		c->src.val &= (c->dst.bytes << 3) - 1;
+		return;
+	}
+
+	if (c->src.bytes == 2)
+		c->src.val = (s16)c->src.val;
+	else if (c->src.bytes == 4)
+		c->src.val = (s32)c->src.val;
+
+	mask = ~(c->dst.bytes * 8 - 1);
+
+	if ((long)c->src.val > 0) {
+		c->dst.addr.mem = c->dst.addr.mem + (c->src.val & mask) / 8;
+		c->src.val &= (c->dst.bytes << 3) - 1;
+	} else {
+		byte_offset = c->dst.bytes + ((-c->src.val - 1) & mask) / 8;
+		c->dst.addr.mem -= byte_offset;
+		c->src.val += byte_offset << 3;
+	}
+}
+
 static int read_emulated(struct x86_emulate_ctxt *ctxt,
 			 struct x86_emulate_ops *ops,
 			 unsigned long addr, void *dest, unsigned size)
@@ -2261,7 +2288,7 @@ static struct opcode twobyte_table[256] = {
 	    D(DstReg | SrcMem16 | ModRM | Mov),
 	/* 0xB8 - 0xBF */
 	N, N,
-	G(0, group8), D(DstMem | SrcReg | ModRM | BitOp | Lock),
+	G(BitOp, group8), D(DstMem | SrcReg | ModRM | BitOp | Lock),
 	N, N, D(ByteOp | DstReg | SrcMem | ModRM | Mov),
 	    D(DstReg | SrcMem16 | ModRM | Mov),
 	/* 0xC0 - 0xCF */
@@ -2587,12 +2614,8 @@ done_prefixes:
 			c->dst.bytes = 8;
 		else
 			c->dst.bytes = (c->d & ByteOp) ? 1 : c->op_bytes;
-		if (c->dst.type == OP_MEM && (c->d & BitOp)) {
-			unsigned long mask = ~(c->dst.bytes * 8 - 1);
-
-			c->dst.addr.mem = c->dst.addr.mem +
-						   (c->src.val & mask) / 8;
-		}
+		if (c->d & BitOp)
+			fetch_bit_operand(c);
 		c->dst.orig_val = c->dst.val;
 		break;
 	case DstAcc:
@@ -3303,8 +3326,6 @@ twobyte_insn:
 	case 0xa3:
 	      bt:		/* bt */
 		c->dst.type = OP_NONE;
-		/* only subword offset */
-		c->src.val &= (c->dst.bytes << 3) - 1;
 		emulate_2op_SrcV_nobyte("bt", c->src, c->dst, ctxt->eflags);
 		break;
 	case 0xa4: /* shld imm8, r, r/m */
@@ -3321,8 +3342,6 @@ twobyte_insn:
 		break;
 	case 0xab:
 	      bts:		/* bts */
-		/* only subword offset */
-		c->src.val &= (c->dst.bytes << 3) - 1;
 		emulate_2op_SrcV_nobyte("bts", c->src, c->dst, ctxt->eflags);
 		break;
 	case 0xac: /* shrd imm8, r, r/m */
@@ -3350,8 +3369,6 @@ twobyte_insn:
 		break;
 	case 0xb3:
 	      btr:		/* btr */
-		/* only subword offset */
-		c->src.val &= (c->dst.bytes << 3) - 1;
 		emulate_2op_SrcV_nobyte("btr", c->src, c->dst, ctxt->eflags);
 		break;
 	case 0xb6 ... 0xb7:	/* movzx */
@@ -3373,8 +3390,6 @@ twobyte_insn:
 		break;
 	case 0xbb:
 	      btc:		/* btc */
-		/* only subword offset */
-		c->src.val &= (c->dst.bytes << 3) - 1;
 		emulate_2op_SrcV_nobyte("btc", c->src, c->dst, ctxt->eflags);
 		break;
 	case 0xbe ... 0xbf:	/* movsx */
-- 
1.7.0.4


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