[PATCH 3.2 036/106] KVM: x86: fix use of uninitialized memory as segment descriptor in emulator.

[Ben Hutchings]

3.2.93-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Gleb Natapov <g...@redhat.com>

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 <g...@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com>
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
 arch/x86/kvm/x86.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4611,8 +4611,10 @@ static bool emulator_get_segment(struct
        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;