KVM: x86: pop sreg accesses only 2 bytes

Although pop sreg updates RSP according to the operand size, only 2 bytes are
read.  The current behavior may result in incorrect #GP or #PF exceptions.
Signed-off-by: NNadav Amit <namit@cs.technion.ac.il>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/emulate.c

@@ -1828,12 +1828,14 @@ static int em_pop_sreg(struct x86_emulate_ctxt *ctxt)
 	unsigned long selector;
 	int rc;
 
-	rc = emulate_pop(ctxt, &selector, ctxt->op_bytes);
+	rc = emulate_pop(ctxt, &selector, 2);
 	if (rc != X86EMUL_CONTINUE)
 		return rc;
 
 	if (ctxt->modrm_reg == VCPU_SREG_SS)
 		ctxt->interruptibility = KVM_X86_SHADOW_INT_MOV_SS;
+	if (ctxt->op_bytes > 2)
+		rsp_increment(ctxt, ctxt->op_bytes - 2);
 
 	rc = load_segment_descriptor(ctxt, (u16)selector, seg);
 	return rc;