$NetBSD: patch-CVE-2012-3494,v 1.1 2012/09/12 11:04:17 drochner Exp $

see http://lists.xen.org/archives/html/xen-devel/2012-09/msg00181.html

--- xen/include/asm-x86/debugreg.h.orig	2012-08-10 13:51:52.000000000 +0000
+++ xen/include/asm-x86/debugreg.h
@@ -58,7 +58,7 @@
    We can slow the instruction pipeline for instructions coming via the
    gdt or the ldt if we want to.  I am not sure why this is an advantage */
 
-#define DR_CONTROL_RESERVED_ZERO (0x0000d800ul) /* Reserved, read as zero */
+#define DR_CONTROL_RESERVED_ZERO (~0xffff27fful) /* Reserved, read as zero */
 #define DR_CONTROL_RESERVED_ONE  (0x00000400ul) /* Reserved, read as one */
 #define DR_LOCAL_EXACT_ENABLE    (0x00000100ul) /* Local exact enable */
 #define DR_GLOBAL_EXACT_ENABLE   (0x00000200ul) /* Global exact enable */
