[Xen-changelog] [xen-4.0-testing] x86/physmap: Prevent incorrect updates of m2p mappings

[Xen patchbot-4.0-testing <patchbot@xxxxxxx>]

# HG changeset patch
# User Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
# Date 1352893251 0
# Node ID 04462a8c79661c3cb939756fb03345901e703493
# Parent  6b9809dc1e860b73d644d7b89435df14f0723657
x86/physmap: Prevent incorrect updates of m2p mappings

In certain conditions, such as low memory, set_p2m_entry() can fail.
Currently, the p2m and m2p tables will get out of sync because we still
update the m2p table after the p2m update has failed.

If that happens, subsequent guest-invoked memory operations can cause
BUG()s and ASSERT()s to kill Xen.

This is fixed by only updating the m2p table iff the p2m was
successfully updated.

This is a security problem, XSA-22 / CVE-2012-4537.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Committed-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---


diff -r 6b9809dc1e86 -r 04462a8c7966 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c     Wed Nov 14 11:37:55 2012 +0000
+++ b/xen/arch/x86/mm/p2m.c     Wed Nov 14 11:40:51 2012 +0000
@@ -2207,7 +2207,10 @@ guest_physmap_add_entry(struct domain *d
     if ( mfn_valid(_mfn(mfn)) ) 
     {
         if ( !set_p2m_entry(d, gfn, _mfn(mfn), page_order, t) )
+        {
             rc = -EINVAL;
+            goto out; /* Failed to update p2m, bail without updating m2p. */
+        }
         if ( !p2m_is_grant(t) )
         {
             for ( i = 0; i < (1UL << page_order); i++ )
@@ -2228,6 +2231,7 @@ guest_physmap_add_entry(struct domain *d
         }
     }
 
+out:
     audit_p2m(d);
     p2m_unlock(d->arch.p2m);
 

_______________________________________________
Xen-changelog mailing list
Xen-changelog@xxxxxxxxxxxxx
http://lists.xensource.com/xen-changelog