KVM: x86: fix use of uninitialized memory as segment descriptor in emulator.

commit 378a8b099fc207ddcb91b19a8c1457667e0af398 upstream.

If VMX reports segment as unusable, zero descriptor passed by the emulator
before returning. Such descriptor will be considered not present by the
emulator.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index eecee50..51bfca6 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4611,8 +4611,10 @@ static bool emulator_get_segment(struct x86_emulate_ctxt *ctxt, u16 *selector,
        kvm_get_segment(emul_to_vcpu(ctxt), &var, seg);
        *selector = var.selector;
 
-       if (var.unusable)
+       if (var.unusable) {
+               memset(desc, 0, sizeof(*desc));
                return false;
+       }
 
        if (var.g)
                var.limit >>= 12;