KVM: x86: IN instruction emulation should ignore REP-prefix

The IN instruction is not be affected by REP-prefix as INS is.  Therefore, the
emulation should ignore the REP prefix as well.  The current emulator
implementation tries to perform writeback when IN instruction with REP-prefix
is emulated. This causes it to perform wrong memory write or spurious #GP
exception to be injected to the guest.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index f3834bbca1d7..e8a58409b5ac 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1324,7 +1324,8 @@ static int pio_in_emulated(struct x86_emulate_ctxt *ctxt,
                 rc->end = n * size;
         }
 
-        if (ctxt->rep_prefix && !(ctxt->eflags & EFLG_DF)) {
+        if (ctxt->rep_prefix && (ctxt->d & String) &&
+            !(ctxt->eflags & EFLG_DF)) {
                 ctxt->dst.data = rc->data + rc->pos;
                 ctxt->dst.type = OP_MEM_STR;
                 ctxt->dst.count = (rc->end - rc->pos) / size;