KVM: VMX: Avoid leaking fake realmode state to userspace

When emulating real mode, we fake some state:

 - tr.base points to a fake vm86 tss
 - segment registers are made to conform to vm86 restrictions

change vmx_get_segment() not to expose this fake state to userspace;
instead, return the original state.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 36 insertions, 7 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index a2e83a9729fc..87ad551b525b 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2032,23 +2032,40 @@ static void vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
         vmcs_writel(GUEST_CR4, hw_cr4);
 }
 
-static u64 vmx_get_segment_base(struct kvm_vcpu *vcpu, int seg)
-{
-        struct kvm_vmx_segment_field *sf = &kvm_vmx_segment_fields[seg];
-
-        return vmcs_readl(sf->base);
-}
-
 static void vmx_get_segment(struct kvm_vcpu *vcpu,
                             struct kvm_segment *var, int seg)
 {
+        struct vcpu_vmx *vmx = to_vmx(vcpu);
         struct kvm_vmx_segment_field *sf = &kvm_vmx_segment_fields[seg];
+        struct kvm_save_segment *save;
         u32 ar;
 
+        if (vmx->rmode.vm86_active
+            && (seg == VCPU_SREG_TR || seg == VCPU_SREG_ES
+                || seg == VCPU_SREG_DS || seg == VCPU_SREG_FS
+                || seg == VCPU_SREG_GS)
+            && !emulate_invalid_guest_state) {
+                switch (seg) {
+                case VCPU_SREG_TR: save = &vmx->rmode.tr; break;
+                case VCPU_SREG_ES: save = &vmx->rmode.es; break;
+                case VCPU_SREG_DS: save = &vmx->rmode.ds; break;
+                case VCPU_SREG_FS: save = &vmx->rmode.fs; break;
+                case VCPU_SREG_GS: save = &vmx->rmode.gs; break;
+                default: BUG();
+                }
+                var->selector = save->selector;
+                var->base = save->base;
+                var->limit = save->limit;
+                ar = save->ar;
+                if (seg == VCPU_SREG_TR
+                    || var->selector == vmcs_read16(sf->selector))
+                        goto use_saved_rmode_seg;
+        }
         var->base = vmcs_readl(sf->base);
         var->limit = vmcs_read32(sf->limit);
         var->selector = vmcs_read16(sf->selector);
         ar = vmcs_read32(sf->ar_bytes);
+use_saved_rmode_seg:
         if ((ar & AR_UNUSABLE_MASK) && !emulate_invalid_guest_state)
                 ar = 0;
         var->type = ar & 15;
@@ -2062,6 +2079,18 @@ static void vmx_get_segment(struct kvm_vcpu *vcpu,
         var->unusable = (ar >> 16) & 1;
 }
 
+static u64 vmx_get_segment_base(struct kvm_vcpu *vcpu, int seg)
+{
+        struct kvm_vmx_segment_field *sf = &kvm_vmx_segment_fields[seg];
+        struct kvm_segment s;
+
+        if (to_vmx(vcpu)->rmode.vm86_active) {
+                vmx_get_segment(vcpu, &s, seg);
+                return s.base;
+        }
+        return vmcs_readl(sf->base);
+}
+
 static int vmx_get_cpl(struct kvm_vcpu *vcpu)
 {
         if (!is_protmode(vcpu))