[QEMU PATCH v4 07/13] softmmu/memory: enable automatic deallocation of memory regions

[Huang Rui <ray.huang@amd.com>]

From: Xenia Ragiadakou <xenia.ragiadakou@amd.com>

When the memory region has a different life-cycle from that of her parent,
could be automatically released, once has been unparent and once all of her
references have gone away, via the object's free callback.

However, currently, references to the memory region are held by its owner
without first incrementing the memory region object's reference count.
As a result, the automatic deallocation of the object, not taking into
account those references, results in use-after-free memory corruption.

This patch increases the reference count of the memory region object on
each memory_region_ref() and decreases it on each memory_region_unref().

Signed-off-by: Xenia Ragiadakou <xenia.ragiadakou@amd.com>
Signed-off-by: Huang Rui <ray.huang@amd.com>
---

New patch

 softmmu/memory.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/softmmu/memory.c b/softmmu/memory.c
index 7d9494ce70..0fdd5eebf9 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -1797,6 +1797,15 @@ Object *memory_region_owner(MemoryRegion *mr)
 
 void memory_region_ref(MemoryRegion *mr)
 {
+    if (!mr) {
+        return;
+    }
+
+    /* Obtain a reference to prevent the memory region object
+     * from being released under our feet.
+     */
+    object_ref(OBJECT(mr));
+
     /* MMIO callbacks most likely will access data that belongs
      * to the owner, hence the need to ref/unref the owner whenever
      * the memory region is in use.
@@ -1807,16 +1816,22 @@ void memory_region_ref(MemoryRegion *mr)
      * Memory regions without an owner are supposed to never go away;
      * we do not ref/unref them because it slows down DMA sensibly.
      */
-    if (mr && mr->owner) {
+    if (mr->owner) {
         object_ref(mr->owner);
     }
 }
 
 void memory_region_unref(MemoryRegion *mr)
 {
-    if (mr && mr->owner) {
+    if (!mr) {
+        return;
+    }
+
+    if (mr->owner) {
         object_unref(mr->owner);
     }
+
+    object_unref(OBJECT(mr));
 }
 
 uint64_t memory_region_size(MemoryRegion *mr)
-- 
2.34.1