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KVM: nVMX: add limit check for expand-down segments

PATCH In review Eugene Korenevsky 2 participants 2 messages Aug 20, 2015 – Sep 7, 2015

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x86 KVM KVM x86
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Eugene Korenevsky

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#0 lore raw

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

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 <[email protected]>
---
 arch/x86/kvm/vmx.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
arch/x86/kvm/vmx.c +4 -1
index faa05a4..4a4d677 100644
@@ -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 ?
Signature · 1 line
2.1.4
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#1 lore raw
Quoted 14 lines · Eugene Korenevsky

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 <[email protected]>
---
 arch/x86/kvm/vmx.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
arch/x86/kvm/vmx.c +0 -0
index faa05a4..4a4d677 100644

arch/x86/kvm/vmx.c static int vmx_protmode_seg_check(struct kvm_vcpu *vcpu, · line 6383

Quoted 8 lines
arch/x86/kvm/vmx.c +4 -1
@@ -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);

For expand-down segments you also have to check against the size of the segment (48 bits for 64-bit segments and positive addresses, 32 bits for 32-bit segments, 16 bits for 16-bit segments; see __linearize in emulate.c).

Paolo