[Xen-changelog] [xen stable-4.8] x86: replace bad ASSERT() in xenmem_add_to_physmap_one()

[patchbot@xxxxxxx]

commit 3effd96e4ae81192fc3073a58a1d72bc1379dcf8
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Dec 20 16:06:49 2017 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Dec 20 16:06:49 2017 +0100

    x86: replace bad ASSERT() in xenmem_add_to_physmap_one()
    
    There are no locks being held, i.e. it is possible to be triggered by
    racy hypercall invocations. Subsequent code doesn't really depend on the
    checked values, so this is not a security issue.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx>
    master commit: f33d653f46f5889db7be4fef31d71bc871834c10
    master date: 2017-11-28 13:14:10 +0100
---
 xen/arch/x86/mm.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 0b9f872..43e0d39 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -5112,8 +5112,12 @@ int xenmem_add_to_physmap_one(
     /* Unmap from old location, if any. */
     old_gpfn = get_gpfn_from_mfn(mfn);
     ASSERT( old_gpfn != SHARED_M2P_ENTRY );
-    if ( space == XENMAPSPACE_gmfn || space == XENMAPSPACE_gmfn_range )
-        ASSERT( old_gpfn == gfn );
+    if ( (space == XENMAPSPACE_gmfn || space == XENMAPSPACE_gmfn_range) &&
+         old_gpfn != gfn )
+    {
+        rc = -EXDEV;
+        goto put_both;
+    }
     if ( old_gpfn != INVALID_M2P_ENTRY )
         rc = guest_physmap_remove_page(d, _gfn(old_gpfn), _mfn(mfn), 
PAGE_ORDER_4K);
 
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.8

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