zephyr: alloc: Add 16MB allocation limit to native_sim host allocator

When building the native_sim fuzzer, the host allocator does not
possess the strict bounds of the internal Zephyr memory pools. If
the fuzzer generates a malformed payload requesting an excessively
large size (e.g. 4GB), it passes directly to the host ASAN allocator
which aborts due to OOM or protection limits. Adding a 16MB cap
allows these to fail gracefully.

Signed-off-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>

Author: lrgirdwo

zephyr/lib/alloc.c

@@ -475,6 +475,11 @@ void *rmalloc_align(uint32_t flags, size_t bytes, uint32_t alignment)
 	void *ptr;
 	void *raw;
 
+	if (bytes > 16 * 1024 * 1024) {
+		tr_err(&zephyr_tr, "rmalloc_align: requested %zu bytes exceeds 16MB limit", bytes);
+		return NULL;
+	}
+
 	if (alignment < sizeof(void *))
 		alignment = sizeof(void *);