[PATCH v4 09/36] mm/slab: introduce SLAB_NO_OBJ_EXT to avoid obj_ext creation

[Suren Baghdasaryan]

Slab extension objects can't be allocated before slab infrastructure is
initialized. Some caches, like kmem_cache and kmem_cache_node, are created
before slab infrastructure is initialized. Objects from these caches can't
have extension objects. Introduce SLAB_NO_OBJ_EXT slab flag to mark these
caches and avoid creating extensions for objects allocated from these
slabs.

Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/linux/slab.h | 6 ++++++
 mm/slub.c            | 5 +++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index b5f5ee8308d0..58794043ab5b 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -28,6 +28,12 @@
  */
 /* DEBUG: Perform (expensive) checks on alloc/free */
 #define SLAB_CONSISTENCY_CHECKS	((slab_flags_t __force)0x00000100U)
+/* Slab created using create_boot_cache */
+#ifdef CONFIG_SLAB_OBJ_EXT
+#define SLAB_NO_OBJ_EXT		((slab_flags_t __force)0x00000200U)
+#else
+#define SLAB_NO_OBJ_EXT		0
+#endif
 /* DEBUG: Red zone objs in a cache */
 #define SLAB_RED_ZONE		((slab_flags_t __force)0x00000400U)
 /* DEBUG: Poison objects */
diff --git a/mm/slub.c b/mm/slub.c
index ca803b2949fc..5dc7beda6c0d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5697,7 +5697,8 @@ void __init kmem_cache_init(void)
 		node_set(node, slab_nodes);
 
 	create_boot_cache(kmem_cache_node, "kmem_cache_node",
-		sizeof(struct kmem_cache_node), SLAB_HWCACHE_ALIGN, 0, 0);
+			sizeof(struct kmem_cache_node),
+			SLAB_HWCACHE_ALIGN | SLAB_NO_OBJ_EXT, 0, 0);
 
 	hotplug_memory_notifier(slab_memory_callback, SLAB_CALLBACK_PRI);
 
@@ -5707,7 +5708,7 @@ void __init kmem_cache_init(void)
 	create_boot_cache(kmem_cache, "kmem_cache",
 			offsetof(struct kmem_cache, node) +
 				nr_node_ids * sizeof(struct kmem_cache_node *),
-		       SLAB_HWCACHE_ALIGN, 0, 0);
+			SLAB_HWCACHE_ALIGN | SLAB_NO_OBJ_EXT, 0, 0);
 
 	kmem_cache = bootstrap(&boot_kmem_cache);
 	kmem_cache_node = bootstrap(&boot_kmem_cache_node);
-- 
2.44.0.rc0.258.g7320e95886-goog