[PATCH v3 2/3] mm/slub: only zero the requested size of buffer for kzalloc

[Feng Tang]

kzalloc/kmalloc will round up the request size to a fixed size
(mostly power of 2), so the allocated memory could be more than
requested. Currently kzalloc family APIs will zero all the
allocated memory.

To detect out-of-bound usage of the extra allocated memory, only
zero the requested part, so that sanity check could be added to
the extra space later.

For kzalloc users who will call ksize() later and utilize this
extra space, please be aware that the space is not zeroed any
more.

Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
---
 mm/slab.c | 8 ++++----
 mm/slab.h | 9 +++++++--
 mm/slub.c | 6 +++---
 3 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index 5e73e2d80222..771f7c57d3ef 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3236,7 +3236,7 @@ slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid, size_t orig_
 	init = slab_want_init_on_alloc(flags, cachep);
 
 out_hooks:
-	slab_post_alloc_hook(cachep, objcg, flags, 1, &ptr, init);
+	slab_post_alloc_hook(cachep, objcg, flags, 1, &ptr, init, 0);
 	return ptr;
 }
 
@@ -3299,7 +3299,7 @@ slab_alloc(struct kmem_cache *cachep, struct list_lru *lru, gfp_t flags,
 	init = slab_want_init_on_alloc(flags, cachep);
 
 out:
-	slab_post_alloc_hook(cachep, objcg, flags, 1, &objp, init);
+	slab_post_alloc_hook(cachep, objcg, flags, 1, &objp, init, 0);
 	return objp;
 }
 
@@ -3546,13 +3546,13 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
 	 * Done outside of the IRQ disabled section.
 	 */
 	slab_post_alloc_hook(s, objcg, flags, size, p,
-				slab_want_init_on_alloc(flags, s));
+				slab_want_init_on_alloc(flags, s), 0);
 	/* FIXME: Trace call missing. Christoph would like a bulk variant */
 	return size;
 error:
 	local_irq_enable();
 	cache_alloc_debugcheck_after_bulk(s, flags, i, p, _RET_IP_);
-	slab_post_alloc_hook(s, objcg, flags, i, p, false);
+	slab_post_alloc_hook(s, objcg, flags, i, p, false, 0);
 	kmem_cache_free_bulk(s, i, p);
 	return 0;
 }
diff --git a/mm/slab.h b/mm/slab.h
index 4ec82bec15ec..7b53868efe6d 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -710,12 +710,17 @@ static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s,
 
 static inline void slab_post_alloc_hook(struct kmem_cache *s,
 					struct obj_cgroup *objcg, gfp_t flags,
-					size_t size, void **p, bool init)
+					size_t size, void **p, bool init,
+					unsigned int orig_size)
 {
 	size_t i;
 
 	flags &= gfp_allowed_mask;
 
+	/* If original request size(kmalloc) is not set, use object_size */
+	if (!orig_size)
+		orig_size = s->object_size;
+
 	/*
 	 * As memory initialization might be integrated into KASAN,
 	 * kasan_slab_alloc and initialization memset must be
@@ -726,7 +731,7 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s,
 	for (i = 0; i < size; i++) {
 		p[i] = kasan_slab_alloc(s, p[i], flags, init);
 		if (p[i] && init && !kasan_has_integrated_init())
-			memset(p[i], 0, s->object_size);
+			memset(p[i], 0, orig_size);
 		kmemleak_alloc_recursive(p[i], s->object_size, 1,
 					 s->flags, flags);
 	}
diff --git a/mm/slub.c b/mm/slub.c
index 2e046cc10b84..946919066a4b 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3285,7 +3285,7 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s, struct list_l
 	init = slab_want_init_on_alloc(gfpflags, s);
 
 out:
-	slab_post_alloc_hook(s, objcg, gfpflags, 1, &object, init);
+	slab_post_alloc_hook(s, objcg, gfpflags, 1, &object, init, orig_size);
 
 	return object;
 }
@@ -3778,11 +3778,11 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
 	 * Done outside of the IRQ disabled fastpath loop.
 	 */
 	slab_post_alloc_hook(s, objcg, flags, size, p,
-				slab_want_init_on_alloc(flags, s));
+				slab_want_init_on_alloc(flags, s), 0);
 	return i;
 error:
 	slub_put_cpu_ptr(s->cpu_slab);
-	slab_post_alloc_hook(s, objcg, flags, i, p, false);
+	slab_post_alloc_hook(s, objcg, flags, i, p, false, 0);
 	kmem_cache_free_bulk(s, i, p);
 	return 0;
 }
-- 
2.27.0