[PATCH v1] memory: assert MemoryRegionOps callbacks are defined

[P J P <ppandit@redhat.com>]

From: Prasad J Pandit <pjp@fedoraproject.org>

When registering a MemoryRegionOps object, assert that its
read/write callback methods are defined. This avoids potential
guest crash via a NULL pointer dereference.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 memory.c | 5 +++++
 1 file changed, 5 insertions(+)

Update v1: add assert while registering MemoryRegionOps
  -> https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg05187.html

diff --git a/memory.c b/memory.c
index 91ceaf9fcf..6e94fd5958 100644
--- a/memory.c
+++ b/memory.c
@@ -1495,6 +1495,9 @@ void memory_region_init_io(MemoryRegion *mr,
                            const char *name,
                            uint64_t size)
 {
+    assert(ops);
+    assert(ops->read);
+    assert(ops->write);
     memory_region_init(mr, owner, name, size);
     mr->ops = ops ? ops : &unassigned_mem_ops;
     mr->opaque = opaque;
@@ -1674,6 +1677,8 @@ void memory_region_init_rom_device_nomigrate(MemoryRegion *mr,
 {
     Error *err = NULL;
     assert(ops);
+    assert(ops->read);
+    assert(ops->write);
     memory_region_init(mr, owner, name, size);
     mr->ops = ops;
     mr->opaque = opaque;
-- 
2.26.2