virtio-balloon: Corrections to address verification

The virtio-balloon device's verification of the address given to it by the
guest has a number of faults:
    * The addresses here are guest physical addresses, which should be
      'hwaddr' rather than 'ram_addr_t' (the distinction is admittedly
      pretty subtle and confusing)
    * We don't check for section.mr being NULL, which is the main way that
      memory_region_find() reports basic failures.  We really need to check
      that before looking at any other section fields, because
      memory_region_find() doesn't initialize them on the failure path
    * We're passing a length of '1' to memory_region_find(), but really the
      guest is requesting that we put the entire page into the balloon,
      so it makes more sense to call it with BALLOON_PAGE_SIZE

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20190214043916.22128-3-david@gibson.dropbear.id.au>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 10 insertions, 7 deletions

diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
index 43af521884..eb357824d8 100644
--- a/hw/virtio/virtio-balloon.c
+++ b/hw/virtio/virtio-balloon.c
@@ -221,17 +221,20 @@ static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
         }
 
         while (iov_to_buf(elem->out_sg, elem->out_num, offset, &pfn, 4) == 4) {
-            ram_addr_t pa;
-            ram_addr_t addr;
+            hwaddr pa;
+            hwaddr addr;
             int p = virtio_ldl_p(vdev, &pfn);
 
-            pa = (ram_addr_t) p << VIRTIO_BALLOON_PFN_SHIFT;
+            pa = (hwaddr) p << VIRTIO_BALLOON_PFN_SHIFT;
             offset += 4;
 
-            /* FIXME: remove get_system_memory(), but how? */
-            section = memory_region_find(get_system_memory(), pa, 1);
-            if (!int128_nz(section.size) ||
-                !memory_region_is_ram(section.mr) ||
+            section = memory_region_find(get_system_memory(), pa,
+                                         BALLOON_PAGE_SIZE);
+            if (!section.mr) {
+                trace_virtio_balloon_bad_addr(pa);
+                continue;
+            }
+            if (!memory_region_is_ram(section.mr) ||
                 memory_region_is_rom(section.mr) ||
                 memory_region_is_romd(section.mr)) {
                 trace_virtio_balloon_bad_addr(pa);