File 26150-x86-shadow-unhook-toplevel-check.patch of Package xen.openSUSE_12.1_Update

References: CVE-2012-4538 XSA-23 bnc#786519

# HG changeset patch
# User Ian Jackson <Ian.Jackson@eu.citrix.com>
# Date 1352893341 0
# Node ID c7a01b6450e483ca839228bf1e1e44de692e3458
# Parent  6b6a4007a6091610a29b71cc32908c74113b852b
xen/mm/shadow: check toplevel pagetables are present before unhooking them.

If the guest has not fully populated its top-level PAE entries when it calls
HVMOP_pagetable_dying, the shadow code could try to unhook entries from
MFN 0.  Add a check to avoid that case.

This issue was introduced by c/s 21239:b9d2db109cf5.

This is a security problem, XSA-23 / CVE-2012-4538.

Signed-off-by: Tim Deegan <tim@xen.org>
Tested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -4737,8 +4737,12 @@ static void sh_pagetable_dying(struct vc
     }
     for ( i = 0; i < 4; i++ )
     {
-        if ( fast_path )
-            smfn = _mfn(pagetable_get_pfn(v->arch.shadow_table[i]));
+        if ( fast_path ) {
+            if ( pagetable_is_null(v->arch.shadow_table[i]) )
+                smfn = _mfn(INVALID_MFN);
+            else
+                smfn = _mfn(pagetable_get_pfn(v->arch.shadow_table[i]));
+        }
         else
         {
             /* retrieving the l2s */