KVM: x86 emulator: disable writeback for TEST
The TEST instruction doesn't write its destination operand. This
could cause problems if an MMIO register was accessed using the TEST
instruction. Recently Windows XP was observed to use TEST against
the APIC ICR; this can cause spurious IPIs.
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index e10fd37..af06539 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1670,6 +1670,8 @@
switch (ctxt->modrm_reg) {
case 0 ... 1: /* test */
emulate_2op_SrcV(ctxt, "test");
+ /* Disable writeback. */
+ ctxt->dst.type = OP_NONE;
break;
case 2: /* not */
ctxt->dst.val = ~ctxt->dst.val;
@@ -2513,6 +2515,8 @@
static int em_test(struct x86_emulate_ctxt *ctxt)
{
emulate_2op_SrcV(ctxt, "test");
+ /* Disable writeback. */
+ ctxt->dst.type = OP_NONE;
return X86EMUL_CONTINUE;
}