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

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Date:   Sat, 09 Sep 2017 22:47:39 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Marcelo Tosatti" <mtosatti@...hat.com>,
        "Gleb Natapov" <gleb@...hat.com>
Subject: [PATCH 3.2 036/106] KVM: x86: fix use of uninitialized memory as
 segment descriptor in emulator.

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

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

From: Gleb Natapov <gleb@...hat.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 <gleb@...hat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.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;