File xsa378-0a.patch of Package xen.20938

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File xsa378-0a.patch of Package xen.20938

# Commit aea270e3f7c0db696c88a0e94b1ece7abd339c84
# Date 2020-02-21 17:14:38 +0100
# Author Jan Beulich <jbeulich@suse.com>
# Committer Jan Beulich <jbeulich@suse.com>
x86/p2m: fix PoD accounting in guest_physmap_add_entry()

The initial observation was that the mfn_valid() check comes too late:
Neither mfn_add() nor mfn_to_page() (let alone de-referencing the
result of the latter) are valid for MFNs failing this check. Move it up
and - noticing that there's no caller doing so - also add an assertion
that this should never produce "false" here.

In turn this would have meant that the "else" to that if() could now go
away, which didn't seem right at all. And indeed, considering callers
like memory_exchange() or various grant table functions, the PoD
accounting should have been outside of that if() from the very
beginning.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -800,6 +800,12 @@ guest_physmap_add_entry(struct domain *d
     if ( p2m_is_foreign(t) )
         return -EINVAL;
 
+    if ( !mfn_valid(mfn) )
+    {
+        ASSERT_UNREACHABLE();
+        return -EINVAL;
+    }
+
     p2m_lock(p2m);
 
     P2M_DEBUG("adding gfn=%#lx mfn=%#lx\n", gfn_x(gfn), mfn_x(mfn));
@@ -900,12 +906,13 @@ guest_physmap_add_entry(struct domain *d
     }
 
     /* Now, actually do the two-way mapping */
-    if ( mfn_valid(mfn) )
+    rc = p2m_set_entry(p2m, gfn, mfn, page_order, t, p2m->default_access);
+    if ( rc == 0 )
     {
-        rc = p2m_set_entry(p2m, gfn, mfn, page_order, t,
-                           p2m->default_access);
-        if ( rc )
-            goto out; /* Failed to update p2m, bail without updating m2p. */
+        pod_lock(p2m);
+        p2m->pod.entry_count -= pod_count;
+        BUG_ON(p2m->pod.entry_count < 0);
+        pod_unlock(p2m);
 
         if ( !p2m_is_grant(t) )
         {
@@ -914,22 +921,7 @@ guest_physmap_add_entry(struct domain *d
                                   gfn_x(gfn_add(gfn, i)));
         }
     }
-    else
-    {
-        gdprintk(XENLOG_WARNING, "Adding bad mfn to p2m map (%#lx -> %#lx)\n",
-                 gfn_x(gfn), mfn_x(mfn));
-        rc = p2m_set_entry(p2m, gfn, INVALID_MFN, page_order,
-                           p2m_invalid, p2m->default_access);
-        if ( rc == 0 )
-        {
-            pod_lock(p2m);
-            p2m->pod.entry_count -= pod_count;
-            BUG_ON(p2m->pod.entry_count < 0);
-            pod_unlock(p2m);
-        }
-    }
 
-out:
     p2m_unlock(p2m);
 
     return rc;

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File xsa378-0a.patch of Package xen.20938

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