xen/mm: make sure node is less than MAX_NUMNODES

The output of MEMF_get_node(memflags) can be as large as nodeid_t can
hold (currently 255).  This is then used as an index to arrays of size
MAX_NUMNODE, which is 64 on x86 and 1 on ARM, can be passed in by an
untrusted guest (via memory_exchange and increase_reservation) and is
not currently bounds-checked.

Check the value in page_alloc.c before using it, and also check the
value in the hypercall call sites and return -EINVAL if appropriate.
Don't permit domains other than the hardware or control domain to
allocate node-constrained memory.

This is CVE-2017-14316 / XSA-231.

Reported-by: Matthew Daley <mattd@bugfuzz.com>
Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 2fece35303
master date: 2017-09-12 14:43:16 +0200

xen/common/memory.c

@@ -390,6 +390,31 @@ static void decrease_reservation(struct memop_args *a)
     a->nr_done = i;
 }
 
+static bool_t propagate_node(unsigned int xmf, unsigned int *memflags)
+{
+    const struct domain *currd = current->domain;
+
+    BUILD_BUG_ON(XENMEMF_get_node(0) != NUMA_NO_NODE);
+    BUILD_BUG_ON(MEMF_get_node(0) != NUMA_NO_NODE);
+
+    if ( XENMEMF_get_node(xmf) == NUMA_NO_NODE )
+        return 1;
+
+    if ( is_hardware_domain(currd) || is_control_domain(currd) )
+    {
+        if ( XENMEMF_get_node(xmf) >= MAX_NUMNODES )
+            return 0;
+
+        *memflags |= MEMF_node(XENMEMF_get_node(xmf));
+        if ( xmf & XENMEMF_exact_node_request )
+            *memflags |= MEMF_exact_node;
+    }
+    else if ( xmf & XENMEMF_exact_node_request )
+        return 0;
+
+    return 1;
+}
+
 static long memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
 {
     struct xen_memory_exchange exch;
@@ -462,6 +487,12 @@ static long memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
         }
     }
 
+    if ( unlikely(!propagate_node(exch.out.mem_flags, &memflags)) )
+    {
+        rc = -EINVAL;
+        goto fail_early;
+    }
+
     d = rcu_lock_domain_by_any_id(exch.in.domid);
     if ( d == NULL )
     {
@@ -480,7 +511,6 @@ static long memory_exchange(XEN_GUEST_HANDLE_PARAM(xen_memory_exchange_t) arg)
         d,
         XENMEMF_get_address_bits(exch.out.mem_flags) ? :
         (BITS_PER_LONG+PAGE_SHIFT)));
-    memflags |= MEMF_node(XENMEMF_get_node(exch.out.mem_flags));
 
     for ( i = (exch.nr_exchanged >> in_chunk_order);
           i < (exch.in.nr_extents >> in_chunk_order);
@@ -834,12 +864,8 @@ static int construct_memop_from_reservation(
         }
         read_unlock(&d->vnuma_rwlock);
     }
-    else
-    {
-        a->memflags |= MEMF_node(XENMEMF_get_node(r->mem_flags));
-        if ( r->mem_flags & XENMEMF_exact_node_request )
-            a->memflags |= MEMF_exact_node;
-    }
+    else if ( unlikely(!propagate_node(r->mem_flags, &a->memflags)) )
+        return -EINVAL;
 
     return 0;
 }

xen/common/page_alloc.c

@@ -711,9 +711,13 @@ static struct page_info *alloc_heap_pages(
         if ( node >= MAX_NUMNODES )
             node = cpu_to_node(smp_processor_id());
     }
+    else if ( unlikely(node >= MAX_NUMNODES) )
+    {
+        ASSERT_UNREACHABLE();
+        return NULL;
+    }
     first_node = node;
 
-    ASSERT(node < MAX_NUMNODES);
     ASSERT(zone_lo <= zone_hi);
     ASSERT(zone_hi < NR_ZONES);