[PATCH] VMX: Fix and improve guest state validity checks

Mohammed Gamal
2010-05-11T16:53:04Z

- Add 's' and 'g' field checks on segment registers
- Correct SS checks for request and descriptor privilege levels

Signed-off-by: Mohammed Gamal <m.gamal005@gmail.com>
---
arch/x86/kvm/vmx.c | 73 +++++++++++++++++++++++++++++++++++++++++++++++----
1 files changed, 67 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 777e00d..9805c2a 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2121,16 +2121,30 @@ static bool stack_segment_valid(struct kvm_vcpu *vcpu)
vmx_get_segment(vcpu, &ss, VCPU_SREG_SS);
ss_rpl = ss.selector & SELECTOR_RPL_MASK;

- if (ss.unusable)
+ if (ss.dpl != ss_rpl) /* DPL != RPL */
+ return false;
+
+ if (ss.unusable) /* Short-circuit */
return true;
+
if (ss.type != 3 && ss.type != 7)
return false;
if (!ss.s)
return false;
- if (ss.dpl != ss_rpl) /* DPL != RPL */
- return false;
if (!ss.present)
return false;
+ if (ss.limit & 0xfff00000) {
+ if ((ss.limit & 0xfff) < 0xfff)
+ return false;
+ if (!ss.g)
+ return false;
+ } else {
+ if ((ss.limit & 0xfff) == 0xfff)
+ return false;
+ if (ss.g)
+ return false;
+ }
+

return true;
}
@@ -2143,8 +2157,15 @@ static bool data_segment_valid(struct kvm_vcpu *vcpu, int seg)
vmx_get_segment(vcpu, &var, seg);
rpl = var.selector & SELECTOR_RPL_MASK;

- if (var.unusable)
+ if (var.unusable) /* Short-circuit */
return true;
+ if (!(var.type & AR_TYPE_ACCESSES_MASK))
+ return false;
+ if (var.type & AR_TYPE_CODE_MASK) {
+ if (!(var.type & AR_TYPE_READABLE_MASK))
+ return false;
+ }
+
if (!var.s)
return false;
if (!var.present)
@@ -2154,6 +2175,18 @@ static bool data_segment_valid(struct kvm_vcpu *vcpu, int seg)
return false;
}

+ if (var.limit & 0xfff00000) {
+ if ((var.limit & 0xfff) < 0xfff)
+ return false;
+ if (!var.g)
+ return false;
+ } else {
+ if ((var.limit & 0xfff) == 0xfff)
+ return false;
+ if (var.g)
+ return false;
+ }
+
/* TODO: Add other members to kvm_segment_field to allow checking for other access
* rights flags
*/
@@ -2172,6 +2205,21 @@ static bool tr_valid(struct kvm_vcpu *vcpu)
return false;
if (tr.type != 3 && tr.type != 11) /* TODO: Check if guest is in IA32e mode */
return false;
+ if (tr.s)
+ return false;
+ if (tr.limit & 0xfff00000) {
+ if ((tr.limit & 0xfff) < 0xfff)
+ return false;
+ if (!tr.g)
+ return false;
+ } else {
+ if ((tr.limit & 0xfff) == 0xfff)
+ return false;
+ if (tr.g)
+ return false;
+ }
+
+
if (!tr.present)
return false;

@@ -2184,7 +2232,7 @@ static bool ldtr_valid(struct kvm_vcpu *vcpu)

vmx_get_segment(vcpu, &ldtr, VCPU_SREG_LDTR);

- if (ldtr.unusable)
+ if (ldtr.unusable) /* Short-circuit */
return true;
if (ldtr.selector & SELECTOR_TI_MASK) /* TI = 1 */
return false;
@@ -2192,6 +2240,20 @@ static bool ldtr_valid(struct kvm_vcpu *vcpu)
return false;
if (!ldtr.present)
return false;
+ if (ldtr.s)
+ return false;
+ if (ldtr.limit & 0xfff00000) {
+ if ((ldtr.limit & 0xfff) < 0xfff)
+ return false;
+ if (!ldtr.g)
+ return false;
+ } else {
+ if ((ldtr.limit & 0xfff) == 0xfff)
+ return false;
+ if (ldtr.g)
+ return false;
+ }
+

return true;
}
@@ -2251,7 +2313,6 @@ static bool guest_state_valid(struct kvm_vcpu *vcpu)
}
/* TODO:
* - Add checks on RIP
- * - Add checks on RFLAGS
*/

return true;
--
1.7.0.4