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authorJuergen Gross <jgross@suse.com>2014-10-14 11:00:18 +0200
committerDavid Vrabel <david.vrabel@citrix.com>2014-10-23 16:24:01 +0100
commit239af7c7132a617f9dcd05da1dc92b96bc6d0645 (patch)
tree74c821845a28a43278cf4522f0871f70dcbb2ba4 /arch
parentfd8b79511349efd1f0decea920f61b93acb34a75 (diff)
x86/xen: avoid writing to freed memory after race in p2m handling
In case a race was detected during allocation of a new p2m tree element in alloc_p2m() the new allocated mid_mfn page is freed without updating the pointer to the found value in the tree. This will result in overwriting the just freed page with the mfn of the p2m leaf. Signed-off-by: Juergen Gross <jgross@suse.com> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/xen/p2m.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 9f5983b01ed9..4534320e66e4 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -566,6 +566,7 @@ static bool alloc_p2m(unsigned long pfn)
/* Separately check the mid mfn level */
unsigned long missing_mfn;
unsigned long mid_mfn_mfn;
+ unsigned long old_mfn;
mid_mfn = alloc_p2m_page();
if (!mid_mfn)
@@ -575,10 +576,13 @@ static bool alloc_p2m(unsigned long pfn)
missing_mfn = virt_to_mfn(p2m_mid_missing_mfn);
mid_mfn_mfn = virt_to_mfn(mid_mfn);
- if (cmpxchg(top_mfn_p, missing_mfn, mid_mfn_mfn) != missing_mfn)
+ old_mfn = cmpxchg(top_mfn_p, missing_mfn, mid_mfn_mfn);
+ if (old_mfn != missing_mfn) {
free_p2m_page(mid_mfn);
- else
+ mid_mfn = mfn_to_virt(old_mfn);
+ } else {
p2m_top_mfn_p[topidx] = mid_mfn;
+ }
}
if (p2m_top[topidx][mididx] == p2m_identity ||