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>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e07b243..814e72a 100644 (file)
--- 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));