KVM: VMX: make rmode_segment_valid() more strict.

Currently it allows entering vm86 mode if segment limit is greater than
0xffff and db bit is set. Both of those can cause incorrect execution of
instruction by cpu since in vm86 mode limit will be set to 0xffff and db
will be forced to 0.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 1 insertions, 3 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 23d5aec78073..7ebcac25725b 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3341,15 +3341,13 @@ static bool rmode_segment_valid(struct kvm_vcpu *vcpu, int seg)
 
         vmx_get_segment(vcpu, &var, seg);
         var.dpl = 0x3;
-        var.g = 0;
-        var.db = 0;
         if (seg == VCPU_SREG_CS)
                 var.type = 0x3;
         ar = vmx_segment_access_rights(&var);
 
         if (var.base != (var.selector << 4))
                 return false;
-        if (var.limit < 0xffff)
+        if (var.limit != 0xffff)
                 return false;
         if (ar != 0xf3)
                 return false;