KVM: x86: Fix uninitialized op->type for some immediate values

commit d29b9d7e upstream.

The emulator could reuse an op->type from a previous instruction for some
immediate values.  If it mistakenly considers the operands as memory
operands, it will performs a memory read and overwrite op->val.

Consider for instance the ROR instruction - src2 (the number of times)
would be read from memory instead of being used as immediate.

Mark every immediate operand as such to avoid this problem.

Fixes: c44b4c6aSigned-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

arch/x86/kvm/emulate.c

@@ -4220,6 +4220,7 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
 		fetch_register_operand(op);
 		break;
 	case OpCL:
+		op->type = OP_IMM;
 		op->bytes = 1;
 		op->val = reg_read(ctxt, VCPU_REGS_RCX) & 0xff;
 		break;
@@ -4227,6 +4228,7 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
 		rc = decode_imm(ctxt, op, 1, true);
 		break;
 	case OpOne:
+		op->type = OP_IMM;
 		op->bytes = 1;
 		op->val = 1;
 		break;
@@ -4285,21 +4287,27 @@ static int decode_operand(struct x86_emulate_ctxt *ctxt, struct operand *op,
 		ctxt->memop.bytes = ctxt->op_bytes + 2;
 		goto mem_common;
 	case OpES:
+		op->type = OP_IMM;
 		op->val = VCPU_SREG_ES;
 		break;
 	case OpCS:
+		op->type = OP_IMM;
 		op->val = VCPU_SREG_CS;
 		break;
 	case OpSS:
+		op->type = OP_IMM;
 		op->val = VCPU_SREG_SS;
 		break;
 	case OpDS:
+		op->type = OP_IMM;
 		op->val = VCPU_SREG_DS;
 		break;
 	case OpFS:
+		op->type = OP_IMM;
 		op->val = VCPU_SREG_FS;
 		break;
 	case OpGS:
+		op->type = OP_IMM;
 		op->val = VCPU_SREG_GS;
 		break;
 	case OpImplicit: