[Xen-changelog] [xen-4.0-testing] xen: only check for shared pages while any exist on teardown

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

# HG changeset patch
# User Ian Campbell <ian.campbell@xxxxxxxxxx>
# Date 1344523639 -3600
# Node ID a51c86b407d732dd66343dea7a6249d2649740c6
# Parent  6d7ae840463c5d6d15c710199b3f4b2bb2a33000
xen: only check for shared pages while any exist on teardown

Avoids worst case behavour when guest has a large p2m.

This is XSA-11 / CVE-2012-3433

Signed-off-by: Tim Deegan <tim@xxxxxxx>
Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Tested-by: Olaf Hering <olaf@xxxxxxxxx>
Committed-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---


diff -r 6d7ae840463c -r a51c86b407d7 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c     Mon Jul 30 13:39:47 2012 +0100
+++ b/xen/arch/x86/mm/p2m.c     Thu Aug 09 15:47:19 2012 +0100
@@ -1725,6 +1725,8 @@ void p2m_teardown(struct domain *d)
 #ifdef __x86_64__
     for ( gfn=0; gfn < p2m->max_mapped_pfn; gfn++ )
     {
+        if ( atomic_read(&d->shr_pages) == 0 )
+            break;
         mfn = p2m->get_entry(d, gfn, &t, p2m_query);
         if ( mfn_valid(mfn) && (t == p2m_ram_shared) )
             BUG_ON(mem_sharing_unshare_page(d, gfn, MEM_SHARING_DESTROY_GFN));

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