x86/P2M: deal with partial success of p2m_set_entry()

M2P and PoD stats need to remain in sync with P2M; if an update succeeds
only partially, respective adjustments need to be made. If updates get
made before the call, they may also need undoing upon complete failure
(i.e. including the single-page case).

Log-dirty state would better also be kept in sync.

Note that the change to set_typed_p2m_entry() may not be strictly
necessary (due to the order restriction enforced near the top of the
function), but is being kept here to be on the safe side.

This is CVE-2021-28705 and CVE-2021-28709 / XSA-389.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
master commit: 74a11c43fd7e074b1f77631b446dd2115eacb9e8
master date: 2021-11-22 12:27:30 +0000

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index f3fdc79ff4df0877e700f40c9674093c15a68f77..266b6a0416ba1eaadcf6d62a03d8ec1cc935029a 100644 (file)
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -780,6 +780,7 @@ p2m_remove_page(struct p2m_domain *p2m, unsigned long gfn_l, unsigned long mfn,
     gfn_t gfn = _gfn(gfn_l);
     p2m_type_t t;
     p2m_access_t a;
+    int rc;
 
     /* IOMMU for PV guests is handled in get_page_type() and put_page(). */
     if ( !paging_mode_translate(p2m->domain) )
@@ -811,8 +812,27 @@ p2m_remove_page(struct p2m_domain *p2m, unsigned long gfn_l, unsigned long mfn,
                 set_gpfn_from_mfn(mfn+i, INVALID_M2P_ENTRY);
         }
     }
-    return p2m_set_entry(p2m, gfn, INVALID_MFN, page_order, p2m_invalid,
-                         p2m->default_access);
+    rc = p2m_set_entry(p2m, gfn, INVALID_MFN, page_order, p2m_invalid,
+                       p2m->default_access);
+    if ( likely(!rc) || !mfn_valid(_mfn(mfn)) )
+        return rc;
+
+    /*
+     * The operation may have partially succeeded. For the failed part we need
+     * to undo the M2P update and, out of precaution, mark the pages dirty
+     * again.
+     */
+    for ( i = 0; i < (1UL << page_order); ++i )
+    {
+        p2m->get_entry(p2m, gfn_add(gfn, i), &t, &a, 0, NULL, NULL);
+        if ( !p2m_is_hole(t) && !p2m_is_special(t) && !p2m_is_shared(t) )
+        {
+            set_gpfn_from_mfn(mfn + i, gfn_l + i);
+            paging_mark_pfn_dirty(p2m->domain, _pfn(gfn_l + i));
+        }
+    }
+
+    return rc;
 }
 
 int
@@ -980,15 +1000,8 @@ guest_physmap_add_entry(struct domain *d, gfn_t gfn, mfn_t mfn,
 
     /* Now, actually do the two-way mapping */
     rc = p2m_set_entry(p2m, gfn, mfn, page_order, t, p2m->default_access);
-    if ( rc == 0 )
+    if ( likely(!rc) )
     {
-#ifdef CONFIG_HVM
-        pod_lock(p2m);
-        p2m->pod.entry_count -= pod_count;
-        BUG_ON(p2m->pod.entry_count < 0);
-        pod_unlock(p2m);
-#endif
-
         if ( !p2m_is_grant(t) )
         {
             for ( i = 0; i < (1UL << page_order); i++ )
@@ -996,6 +1009,44 @@ guest_physmap_add_entry(struct domain *d, gfn_t gfn, mfn_t mfn,
                                   gfn_x(gfn_add(gfn, i)));
         }
     }
+    else
+    {
+        /*
+         * The operation may have partially succeeded. For the successful part
+         * we need to update M2P and dirty state, while for the failed part we
+         * may need to adjust PoD stats as well as undo the earlier M2P update.
+         */
+        for ( i = 0; i < (1UL << page_order); ++i )
+        {
+            omfn = p2m->get_entry(p2m, gfn_add(gfn, i), &ot, &a, 0, NULL, NULL);
+            if ( p2m_is_pod(ot) )
+            {
+                BUG_ON(!pod_count);
+                --pod_count;
+            }
+            else if ( mfn_eq(omfn, mfn_add(mfn, i)) && ot == t &&
+                      a == p2m->default_access && !p2m_is_grant(t) )
+            {
+                set_gpfn_from_mfn(mfn_x(omfn), gfn_x(gfn) + i);
+                paging_mark_pfn_dirty(d, _pfn(gfn_x(gfn) + i));
+            }
+            else if ( p2m_is_ram(ot) && !p2m_is_paged(ot) )
+            {
+                ASSERT(mfn_valid(omfn));
+                set_gpfn_from_mfn(mfn_x(omfn), gfn_x(gfn) + i);
+            }
+        }
+    }
+
+#ifdef CONFIG_HVM
+    if ( pod_count )
+    {
+        pod_lock(p2m);
+        p2m->pod.entry_count -= pod_count;
+        BUG_ON(p2m->pod.entry_count < 0);
+        pod_unlock(p2m);
+    }
+#endif
 
  out:
     p2m_unlock(p2m);
@@ -1278,6 +1329,49 @@ static int set_typed_p2m_entry(struct domain *d, unsigned long gfn_l,
         domain_crash(d);
         return -EPERM;
     }
+
+    P2M_DEBUG("set %d %lx %lx\n", gfn_p2mt, gfn_l, mfn_x(mfn));
+    rc = p2m_set_entry(p2m, gfn, mfn, order, gfn_p2mt, access);
+    if ( unlikely(rc) )
+    {
+        gdprintk(XENLOG_ERR, "p2m_set_entry: %#lx:%u -> %d (0x%"PRI_mfn")\n",
+                 gfn_l, order, rc, mfn_x(mfn));
+
+        /*
+         * The operation may have partially succeeded. For the successful part
+         * we need to update PoD stats, M2P, and dirty state.
+         */
+        if ( order != PAGE_ORDER_4K )
+        {
+            unsigned long i;
+
+            for ( i = 0; i < (1UL << order); ++i )
+            {
+                p2m_type_t t;
+                mfn_t cmfn = p2m->get_entry(p2m, gfn_add(gfn, i), &t, &a, 0,
+                                            NULL, NULL);
+
+                if ( !mfn_eq(cmfn, mfn_add(mfn, i)) || t != gfn_p2mt ||
+                     a != access )
+                    continue;
+
+                if ( p2m_is_ram(ot) )
+                {
+                    ASSERT(mfn_valid(mfn_add(omfn, i)));
+                    set_gpfn_from_mfn(mfn_x(omfn) + i, INVALID_M2P_ENTRY);
+                }
+#ifdef CONFIG_HVM
+                else if ( p2m_is_pod(ot) )
+                {
+                    pod_lock(p2m);
+                    BUG_ON(!p2m->pod.entry_count);
+                    --p2m->pod.entry_count;
+                    pod_unlock(p2m);
+                }
+#endif
+            }
+        }
+    }
     else if ( p2m_is_ram(ot) )
     {
         unsigned long i;
@@ -1288,12 +1382,6 @@ static int set_typed_p2m_entry(struct domain *d, unsigned long gfn_l,
             set_gpfn_from_mfn(mfn_x(omfn) + i, INVALID_M2P_ENTRY);
         }
     }
-
-    P2M_DEBUG("set %d %lx %lx\n", gfn_p2mt, gfn_l, mfn_x(mfn));
-    rc = p2m_set_entry(p2m, gfn, mfn, order, gfn_p2mt, access);
-    if ( rc )
-        gdprintk(XENLOG_ERR, "p2m_set_entry: %#lx:%u -> %d (0x%"PRI_mfn")\n",
-                 gfn_l, order, rc, mfn_x(mfn));
 #ifdef CONFIG_HVM
     else if ( p2m_is_pod(ot) )
     {