KVM: fix segment_base() error checking

fix segment_base() to properly check for null segment selector and
avoid accessing NULL pointer if ldt selector in null.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e07b243055f8..814e72a02eff 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -230,7 +230,7 @@ unsigned long segment_base(u16 selector)
         unsigned long table_base;
         unsigned long v;
 
-        if (selector == 0)
+        if (!(selector & ~3))
                 return 0;
 
         native_store_gdt(&gdt);
@@ -239,6 +239,8 @@ unsigned long segment_base(u16 selector)
         if (selector & 4) {           /* from ldt */
                 u16 ldt_selector = kvm_read_ldt();
 
+                if (!(ldt_selector & ~3))
+                        return 0;
                 table_base = segment_base(ldt_selector);
         }
         d = (struct desc_struct *)(table_base + (selector & ~7));