KVM: VMX: Add Guest State Validity Checks

This patch adds functions to check whether guest state is VMX compliant.

Signed-off-by: Mohammed Gamal <m.gamal005@gmail.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 180 insertions, 0 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 81db7d48ab80..e889b768c751 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1721,6 +1721,186 @@ static void vmx_set_gdt(struct kvm_vcpu *vcpu, struct descriptor_table *dt)
         vmcs_writel(GUEST_GDTR_BASE, dt->base);
 }
 
+static bool rmode_segment_valid(struct kvm_vcpu *vcpu, int seg)
+{
+        struct kvm_segment var;
+        u32 ar;
+
+        vmx_get_segment(vcpu, &var, seg);
+        ar = vmx_segment_access_rights(&var);
+
+        if (var.base != (var.selector << 4))
+                return false;
+        if (var.limit != 0xffff)
+                return false;
+        if (ar != 0xf3)
+                return false;
+
+        return true;
+}
+
+static bool code_segment_valid(struct kvm_vcpu *vcpu)
+{
+        struct kvm_segment cs;
+        unsigned int cs_rpl;
+
+        vmx_get_segment(vcpu, &cs, VCPU_SREG_CS);
+        cs_rpl = cs.selector & SELECTOR_RPL_MASK;
+
+        if (~cs.type & (AR_TYPE_CODE_MASK|AR_TYPE_ACCESSES_MASK))
+                return false;
+        if (!cs.s)
+                return false;
+        if (!(~cs.type & (AR_TYPE_CODE_MASK|AR_TYPE_WRITEABLE_MASK))) {
+                if (cs.dpl > cs_rpl)
+                        return false;
+        } else if (cs.type & AR_TYPE_CODE_MASK) {
+                if (cs.dpl != cs_rpl)
+                        return false;
+        }
+        if (!cs.present)
+                return false;
+
+        /* TODO: Add Reserved field check, this'll require a new member in the kvm_segment_field structure */
+        return true;
+}
+
+static bool stack_segment_valid(struct kvm_vcpu *vcpu)
+{
+        struct kvm_segment ss;
+        unsigned int ss_rpl;
+
+        vmx_get_segment(vcpu, &ss, VCPU_SREG_SS);
+        ss_rpl = ss.selector & SELECTOR_RPL_MASK;
+
+        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;
+
+        return true;
+}
+
+static bool data_segment_valid(struct kvm_vcpu *vcpu, int seg)
+{
+        struct kvm_segment var;
+        unsigned int rpl;
+
+        vmx_get_segment(vcpu, &var, seg);
+        rpl = var.selector & SELECTOR_RPL_MASK;
+
+        if (!var.s)
+                return false;
+        if (!var.present)
+                return false;
+        if (~var.type & (AR_TYPE_CODE_MASK|AR_TYPE_WRITEABLE_MASK)) {
+                if (var.dpl < rpl) /* DPL < RPL */
+                        return false;
+        }
+
+        /* TODO: Add other members to kvm_segment_field to allow checking for other access
+         * rights flags
+         */
+        return true;
+}
+
+static bool tr_valid(struct kvm_vcpu *vcpu)
+{
+        struct kvm_segment tr;
+
+        vmx_get_segment(vcpu, &tr, VCPU_SREG_TR);
+
+        if (tr.selector & SELECTOR_TI_MASK)     /* TI = 1 */
+                return false;
+        if ((tr.type != 3) || (tr.type != 11)) /* TODO: Check if guest is in IA32e mode */
+                return false;
+        if (!tr.present)
+                return false;
+
+        return true;
+}
+
+static bool ldtr_valid(struct kvm_vcpu *vcpu)
+{
+        struct kvm_segment ldtr;
+
+        vmx_get_segment(vcpu, &ldtr, VCPU_SREG_LDTR);
+
+        if (ldtr.selector & SELECTOR_TI_MASK)   /* TI = 1 */
+                return false;
+        if (ldtr.type != 2)
+                return false;
+        if (!ldtr.present)
+                return false;
+
+        return true;
+}
+
+static bool cs_ss_rpl_check(struct kvm_vcpu *vcpu)
+{
+        struct kvm_segment cs, ss;
+
+        vmx_get_segment(vcpu, &cs, VCPU_SREG_CS);
+        vmx_get_segment(vcpu, &ss, VCPU_SREG_SS);
+
+        return ((cs.selector & SELECTOR_RPL_MASK) ==
+                 (ss.selector & SELECTOR_RPL_MASK));
+}
+
+/*
+ * Check if guest state is valid. Returns true if valid, false if
+ * not.
+ * We assume that registers are always usable
+ */
+static bool guest_state_valid(struct kvm_vcpu *vcpu)
+{
+        /* real mode guest state checks */
+        if (!(vcpu->arch.cr0 & X86_CR0_PE)) {
+                if (!rmode_segment_valid(vcpu, VCPU_SREG_CS))
+                        return false;
+                if (!rmode_segment_valid(vcpu, VCPU_SREG_SS))
+                        return false;
+                if (!rmode_segment_valid(vcpu, VCPU_SREG_DS))
+                        return false;
+                if (!rmode_segment_valid(vcpu, VCPU_SREG_ES))
+                        return false;
+                if (!rmode_segment_valid(vcpu, VCPU_SREG_FS))
+                        return false;
+                if (!rmode_segment_valid(vcpu, VCPU_SREG_GS))
+                        return false;
+        } else {
+        /* protected mode guest state checks */
+                if (!cs_ss_rpl_check(vcpu))
+                        return false;
+                if (!code_segment_valid(vcpu))
+                        return false;
+                if (!stack_segment_valid(vcpu))
+                        return false;
+                if (!data_segment_valid(vcpu, VCPU_SREG_DS))
+                        return false;
+                if (!data_segment_valid(vcpu, VCPU_SREG_ES))
+                        return false;
+                if (!data_segment_valid(vcpu, VCPU_SREG_FS))
+                        return false;
+                if (!data_segment_valid(vcpu, VCPU_SREG_GS))
+                        return false;
+                if (!tr_valid(vcpu))
+                        return false;
+                if (!ldtr_valid(vcpu))
+                        return false;
+        }
+        /* TODO:
+         * - Add checks on RIP
+         * - Add checks on RFLAGS
+         */
+
+        return true;
+}
+
 static int init_rmode_tss(struct kvm *kvm)
 {
         gfn_t fn = rmode_tss_base(kvm) >> PAGE_SHIFT;