mm/slub, kunit: Add a test case for kmalloc redzone check

kmalloc redzone check for slub has been merged, and it's better to add
a kunit case for it, which is inspired by a real-world case as described
in commit 120ee599 ("staging: octeon-usb: prevent memory corruption"):

"
  octeon-hcd will crash the kernel when SLOB is used. This usually happens
  after the 18-byte control transfer when a device descriptor is read.
  The DMA engine is always transferring full 32-bit words and if the
  transfer is shorter, some random garbage appears after the buffer.
  The problem is not visible with SLUB since it rounds up the allocations
  to word boundary, and the extra bytes will go undetected.
"

To avoid interrupting the normal functioning of kmalloc caches, a
kmem_cache mimicing kmalloc cache is created with similar flags, and
kmalloc_trace() is used to really test the orig_size and redzone setup.
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Feng Tang <feng.tang@intel.com>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

lib/slub_kunit.c

@@ -135,6 +135,27 @@ static void test_clobber_redzone_free(struct kunit *test)
 	kmem_cache_destroy(s);
 }
 
+static void test_kmalloc_redzone_access(struct kunit *test)
+{
+	struct kmem_cache *s = test_kmem_cache_create("TestSlub_RZ_kmalloc", 32,
+				SLAB_KMALLOC|SLAB_STORE_USER|SLAB_RED_ZONE);
+	u8 *p = kmalloc_trace(s, GFP_KERNEL, 18);
+
+	kasan_disable_current();
+
+	/* Suppress the -Warray-bounds warning */
+	OPTIMIZER_HIDE_VAR(p);
+	p[18] = 0xab;
+	p[19] = 0xab;
+
+	validate_slab_cache(s);
+	KUNIT_EXPECT_EQ(test, 2, slab_errors);
+
+	kasan_enable_current();
+	kmem_cache_free(s, p);
+	kmem_cache_destroy(s);
+}
+
 static int test_init(struct kunit *test)
 {
 	slab_errors = 0;
@@ -154,6 +175,7 @@ static struct kunit_case test_cases[] = {
 #endif
 
 	KUNIT_CASE(test_clobber_redzone_free),
+	KUNIT_CASE(test_kmalloc_redzone_access),
 	{}
 };
 

mm/slab.h

@@ -336,7 +336,8 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
 			  SLAB_ACCOUNT)
 #elif defined(CONFIG_SLUB)
 #define SLAB_CACHE_FLAGS (SLAB_NOLEAKTRACE | SLAB_RECLAIM_ACCOUNT | \
-			  SLAB_TEMPORARY | SLAB_ACCOUNT | SLAB_NO_USER_FLAGS)
+			  SLAB_TEMPORARY | SLAB_ACCOUNT | \
+			  SLAB_NO_USER_FLAGS | SLAB_KMALLOC)
 #else
 #define SLAB_CACHE_FLAGS (SLAB_NOLEAKTRACE)
 #endif
@@ -356,6 +357,7 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
 			      SLAB_RECLAIM_ACCOUNT | \
 			      SLAB_TEMPORARY | \
 			      SLAB_ACCOUNT | \
+			      SLAB_KMALLOC | \
 			      SLAB_NO_USER_FLAGS)
 
 bool __kmem_cache_empty(struct kmem_cache *);