[PATCH 3/5] KVM: nVMX: add limit check for expand-down segments

[Eugene Korenevsky <ekorenevsky@gmail.com>]

Add limit checking for expand-down data segments. For such segments, the
effective limit specifies the last address that is not allowed to be accessed
within the segment. I.e. offset <= limit means means limit exceeding.

Signed-off-by: Eugene Korenevsky <ekorenevsky@gmail.com>
---
 arch/x86/kvm/vmx.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index faa05a4..4a4d677 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6377,7 +6377,10 @@ static int vmx_protmode_seg_check(struct kvm_vcpu *vcpu,
 	/* #GP(0)/#SS(0) if the segment is unusable. */
 	exn = (s->unusable != 0);
 	/* #GP(0)/#SS(0) if the memory operand is outside the segment limit. */
-	exn = exn || (off + mem_op_size - 1 > s->limit);
+	if (!(s->type & 8) && (s->type & 4)) /* expand-down segment? */
+		exn = exn || (off <= s->limit);
+	else
+		exn = exn || (off + mem_op_size - 1 > s->limit);
 	if (exn) {
 		kvm_queue_exception_e(vcpu,
 				      seg == VCPU_SREG_SS ?
-- 
2.1.4