[Xen-devel] [PATCH 1/3] x86: replace bad ASSERT() in xenmem_add_to_physmap_one()

["Jan Beulich" <JBeulich@xxxxxxxx>]

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>
---
I'm up for to better suggestions for the EXDEV I've used; I certainly
don't want to use -EINVAL, and -EAGAIN (afaik) generally is meant as a
hint to re-invoke with the same arguments (which wouldn't help here).

--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -4143,8 +4143,12 @@ int xenmem_add_to_physmap_one(
     /* Unmap from old location, if any. */
     old_gpfn = get_gpfn_from_mfn(mfn_x(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, PAGE_ORDER_4K);
 




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