x86/p2m: guard (in particular) identity mapping entries

Such entries, created by set_identity_p2m_entry(), should only be
destroyed by clear_identity_p2m_entry(). However, similarly, entries
created by set_mmio_p2m_entry() should only be torn down by
clear_mmio_p2m_entry(), so the logic gets based upon p2m_mmio_direct as
the entry type (separation between "ordinary" and 1:1 mappings would
require a further indicator to tell apart the two).

As to the guest_remove_page() change, commit 48dfb297a20a ("x86/PVH:
allow guest_remove_page to remove p2m_mmio_direct pages"), which
introduced the call to clear_mmio_p2m_entry(), claimed this was done for
hwdom only without this actually having been the case. However, this
code shouldn't be there in the first place, as MMIO entries shouldn't be
dropped this way. Avoid triggering the warning again that 48dfb297a20a
silenced by an adjustment to xenmem_add_to_physmap_one() instead.

Note that guest_physmap_mark_populate_on_demand() gets tightened beyond
the immediate purpose of this change.

Note also that I didn't inspect code which isn't security supported,
e.g. sharing, paging, or altp2m.

This is CVE-2021-28694 / part of XSA-378.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Paul Durrant <paul@xen.org>
master commit: 753cb68e653002e89fdcd1c80e52905fdbfb78cb
master date: 2021-08-25 14:17:32 +0200

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index e56cd4bc65493ce8ce5fc533427d9d224c43888c..1f3b12d44723782e3479fab30649ba9b4896479e 100644 (file)
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -4770,7 +4770,9 @@ int xenmem_add_to_physmap_one(
 
     /* Remove previously mapped page if it was present. */
     prev_mfn = get_gfn(d, gfn_x(gpfn), &p2mt);
-    if ( mfn_valid(prev_mfn) )
+    if ( p2mt == p2m_mmio_direct )
+        rc = -EPERM;
+    else if ( mfn_valid(prev_mfn) )
     {
         if ( is_xen_heap_mfn(prev_mfn) )
             /* Xen heap frames are simply unhooked from this phys slot. */

diff --git a/xen/arch/x86/mm/p2m-pod.c b/xen/arch/x86/mm/p2m-pod.c
index 096e2773fb5a913b2c70877f0e0affd8dae42139..007cdd87d07c5dbea5f3deae289d5aa557863a54 100644 (file)
--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -1295,17 +1295,17 @@ guest_physmap_mark_populate_on_demand(struct domain *d, unsigned long gfn_l,
 
         p2m->get_entry(p2m, gfn_add(gfn, i), &ot, &a, 0, &cur_order, NULL);
         n = 1UL << min(order, cur_order);
-        if ( p2m_is_ram(ot) )
+        if ( ot == p2m_populate_on_demand )
+        {
+            /* Count how many PoD entries we'll be replacing if successful */
+            pod_count += n;
+        }
+        else if ( ot != p2m_invalid && ot != p2m_mmio_dm )
         {
             P2M_DEBUG("gfn_to_mfn returned type %d!\n", ot);
             rc = -EBUSY;
             goto out;
         }
-        else if ( ot == p2m_populate_on_demand )
-        {
-            /* Count how man PoD entries we'll be replacing if successful */
-            pod_count += n;
-        }
     }
 
     /* Now, actually do the two-way mapping */

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 96fbed8ce179002f8641ff16de439eaa73b7356f..2e4d6e52a28239129d2d123577538e56dd552f5a 100644 (file)
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -796,7 +796,8 @@ p2m_remove_page(struct p2m_domain *p2m, unsigned long gfn_l, unsigned long mfn,
                                           &cur_order, NULL);
 
         if ( p2m_is_valid(t) &&
-             (!mfn_valid(_mfn(mfn)) || mfn + i != mfn_x(mfn_return)) )
+             (!mfn_valid(_mfn(mfn)) || t == p2m_mmio_direct ||
+              mfn + i != mfn_x(mfn_return)) )
             return -EILSEQ;
 
         i += (1UL << cur_order) - ((gfn_l + i) & ((1UL << cur_order) - 1));
@@ -890,7 +891,7 @@ guest_physmap_add_entry(struct domain *d, gfn_t gfn, mfn_t mfn,
     if ( p2m_is_foreign(t) )
         return -EINVAL;
 
-    if ( !mfn_valid(mfn) )
+    if ( !mfn_valid(mfn) || t == p2m_mmio_direct )
     {
         ASSERT_UNREACHABLE();
         return -EINVAL;
@@ -936,7 +937,7 @@ guest_physmap_add_entry(struct domain *d, gfn_t gfn, mfn_t mfn,
         }
         if ( p2m_is_special(ot) )
         {
-            /* Don't permit unmapping grant/foreign this way. */
+            /* Don't permit unmapping grant/foreign/direct-MMIO this way. */
             domain_crash(d);
             p2m_unlock(p2m);
             
@@ -1385,8 +1386,8 @@ int set_identity_p2m_entry(struct domain *d, unsigned long gfn_l,
  *    order+1  for caller to retry with order (guaranteed smaller than
  *             the order value passed in)
  */
-int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn_l, mfn_t mfn,
-                         unsigned int order)
+static int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn_l,
+                                mfn_t mfn, unsigned int order)
 {
     int rc = -EINVAL;
     gfn_t gfn = _gfn(gfn_l);

diff --git a/xen/common/memory.c b/xen/common/memory.c
index 4c982f3db7a3a1653c67c805e36cd70b36314558..7c394b36403c9dad171bd959cf5907b2998fc516 100644 (file)
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -328,7 +328,7 @@ int guest_remove_page(struct domain *d, unsigned long gmfn)
     }
     if ( p2mt == p2m_mmio_direct )
     {
-        rc = clear_mmio_p2m_entry(d, gmfn, mfn, PAGE_ORDER_4K);
+        rc = -EPERM;
         goto out_put_gfn;
     }
 #else
@@ -1720,6 +1720,15 @@ int check_get_page_from_gfn(struct domain *d, gfn_t gfn, bool readonly,
         return -EAGAIN;
     }
 #endif
+#ifdef CONFIG_X86
+    if ( p2mt == p2m_mmio_direct )
+    {
+        if ( page )
+            put_page(page);
+
+        return -EPERM;
+    }
+#endif
 
     if ( !page )
         return -EINVAL;

diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index 3b28d2a1b8236364f936834813228847b535deed..807dc4b1a9e811d2716779c7e8a83d3bd8239e5d 100644 (file)
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -143,7 +143,8 @@ typedef unsigned int p2m_query_t;
 
 /* Types established/cleaned up via special accessors. */
 #define P2M_SPECIAL_TYPES (P2M_GRANT_TYPES | \
-                           p2m_to_mask(p2m_map_foreign))
+                           p2m_to_mask(p2m_map_foreign) | \
+                           p2m_to_mask(p2m_mmio_direct))
 
 /* Valid types not necessarily associated with a (valid) MFN. */
 #define P2M_INVALID_MFN_TYPES (P2M_POD_TYPES                  \
@@ -649,8 +650,6 @@ int set_foreign_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn);
 /* Set mmio addresses in the p2m table (for pass-through) */
 int set_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
                        unsigned int order, p2m_access_t access);
-int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
-                         unsigned int order);
 
 /* Set identity addresses in the p2m table (for pass-through) */
 int set_identity_p2m_entry(struct domain *d, unsigned long gfn,