Date:	Thu,  4 Feb 2016 15:15:50 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: [PATCH] mm/slub: support left red zone

SLUB already has red zone debugging feature. But, it is only positioned
at the end of object(aka right red zone) so it cannot catch left oob.
Although current object's right red zone acts as left red zone of
previous object, first object in a slab cannot take advantage of
this effect. This patch explicitly add left red zone to each objects
to detect left oob more precisely.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
---
 include/linux/slub_def.h |   1 +
 mm/slub.c                | 158 ++++++++++++++++++++++++++++++++++-------------
 2 files changed, 115 insertions(+), 44 deletions(-)

diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index b7e57927..a33869b 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -77,6 +77,7 @@ struct kmem_cache {
 	int refcount;		/* Refcount for slab cache destroy */
 	void (*ctor)(void *);
 	int inuse;		/* Offset to metadata */
+	int red_left_pad;	/* Left redzone padding size */
 	int align;		/* Alignment */
 	int reserved;		/* Reserved bytes at the end of slabs */
 	const char *name;	/* Name (only for display!) */
diff --git a/mm/slub.c b/mm/slub.c
index 7b5a965..7216769 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -39,6 +39,10 @@
 
 #include "internal.h"
 
+#ifdef CONFIG_KASAN
+#include "kasan/kasan.h"
+#endif
+
 /*
  * Lock order:
  *   1. slab_mutex (Global Mutex)
@@ -124,6 +128,14 @@ static inline int kmem_cache_debug(struct kmem_cache *s)
 #endif
 }
 
+static inline void *fixup_red_left(struct kmem_cache *s, void *p)
+{
+	if (kmem_cache_debug(s) && s->flags & SLAB_RED_ZONE)
+		p += s->red_left_pad;
+
+	return p;
+}
+
 static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s)
 {
 #ifdef CONFIG_SLUB_CPU_PARTIAL
@@ -224,24 +236,6 @@ static inline void stat(const struct kmem_cache *s, enum stat_item si)
  * 			Core slab cache functions
  *******************************************************************/
 
-/* Verify that a pointer has an address that is valid within a slab page */
-static inline int check_valid_pointer(struct kmem_cache *s,
-				struct page *page, const void *object)
-{
-	void *base;
-
-	if (!object)
-		return 1;
-
-	base = page_address(page);
-	if (object < base || object >= base + page->objects * s->size ||
-		(object - base) % s->size) {
-		return 0;
-	}
-
-	return 1;
-}
-
 static inline void *get_freepointer(struct kmem_cache *s, void *object)
 {
 	return *(void **)(object + s->offset);
@@ -435,6 +429,22 @@ static void get_map(struct kmem_cache *s, struct page *page, unsigned long *map)
 		set_bit(slab_index(p, s, addr), map);
 }
 
+static inline int size_from_object(struct kmem_cache *s)
+{
+	if (s->flags & SLAB_RED_ZONE)
+		return s->size - s->red_left_pad;
+
+	return s->size;
+}
+
+static inline void *restore_red_left(struct kmem_cache *s, void *p)
+{
+	if (s->flags & SLAB_RED_ZONE)
+		p -= s->red_left_pad;
+
+	return p;
+}
+
 /*
  * Debug settings:
  */
@@ -468,6 +478,26 @@ static inline void metadata_access_disable(void)
 /*
  * Object debugging
  */
+
+/* Verify that a pointer has an address that is valid within a slab page */
+static inline int check_valid_pointer(struct kmem_cache *s,
+				struct page *page, void *object)
+{
+	void *base;
+
+	if (!object)
+		return 1;
+
+	base = page_address(page);
+	object = restore_red_left(s, object);
+	if (object < base || object >= base + page->objects * s->size ||
+		(object - base) % s->size) {
+		return 0;
+	}
+
+	return 1;
+}
+
 static void print_section(char *text, u8 *addr, unsigned int length)
 {
 	metadata_access_enable();
@@ -607,7 +637,9 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
 	pr_err("INFO: Object 0x%p @offset=%tu fp=0x%p\n\n",
 	       p, p - addr, get_freepointer(s, p));
 
-	if (p > addr + 16)
+	if (s->flags & SLAB_RED_ZONE)
+		print_section("Redzone ", p - s->red_left_pad, s->red_left_pad);
+	else if (p > addr + 16)
 		print_section("Bytes b4 ", p - 16, 16);
 
 	print_section("Object ", p, min_t(unsigned long, s->object_size,
@@ -624,9 +656,9 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
 	if (s->flags & SLAB_STORE_USER)
 		off += 2 * sizeof(struct track);
 
-	if (off != s->size)
+	if (off != size_from_object(s))
 		/* Beginning of the filler is the free pointer */
-		print_section("Padding ", p + off, s->size - off);
+		print_section("Padding ", p + off, size_from_object(s) - off);
 
 	dump_stack();
 }
@@ -656,6 +688,9 @@ static void init_object(struct kmem_cache *s, void *object, u8 val)
 {
 	u8 *p = object;
 
+	if (s->flags & SLAB_RED_ZONE)
+		memset(p - s->red_left_pad, val, s->red_left_pad);
+
 	if (s->flags & __OBJECT_POISON) {
 		memset(p, POISON_FREE, s->object_size - 1);
 		p[s->object_size - 1] = POISON_END;
@@ -748,11 +783,11 @@ static int check_pad_bytes(struct kmem_cache *s, struct page *page, u8 *p)
 		/* We also have user information there */
 		off += 2 * sizeof(struct track);
 
-	if (s->size == off)
+	if (size_from_object(s) == off)
 		return 1;
 
 	return check_bytes_and_report(s, page, p, "Object padding",
-				p + off, POISON_INUSE, s->size - off);
+			p + off, POISON_INUSE, size_from_object(s) - off);
 }
 
 /* Check the pad bytes at the end of a slab page */
@@ -797,6 +832,10 @@ static int check_object(struct kmem_cache *s, struct page *page,
 
 	if (s->flags & SLAB_RED_ZONE) {
 		if (!check_bytes_and_report(s, page, object, "Redzone",
+			object - s->red_left_pad, val, s->red_left_pad))
+			return 0;
+
+		if (!check_bytes_and_report(s, page, object, "Redzone",
 			endobject, val, s->inuse - s->object_size))
 			return 0;
 	} else {
@@ -998,14 +1037,17 @@ static inline void dec_slabs_node(struct kmem_cache *s, int node, int objects)
 }
 
 /* Object debug checks for alloc/free paths */
-static void setup_object_debug(struct kmem_cache *s, struct page *page,
+static void *setup_object_debug(struct kmem_cache *s, struct page *page,
 								void *object)
 {
 	if (!(s->flags & (SLAB_STORE_USER|SLAB_RED_ZONE|__OBJECT_POISON)))
-		return;
+		return object;
 
+	object = fixup_red_left(s, object);
 	init_object(s, object, SLUB_RED_INACTIVE);
 	init_tracking(s, object);
+
+	return object;
 }
 
 static noinline int alloc_debug_processing(struct kmem_cache *s,
@@ -1202,8 +1244,8 @@ unsigned long kmem_cache_flags(unsigned long object_size,
 	return flags;
 }
 #else /* !CONFIG_SLUB_DEBUG */
-static inline void setup_object_debug(struct kmem_cache *s,
-			struct page *page, void *object) {}
+static inline void *setup_object_debug(struct kmem_cache *s,
+			struct page *page, void *object) { return object; }
 
 static inline int alloc_debug_processing(struct kmem_cache *s,
 	struct page *page, void *object, unsigned long addr) { return 0; }
@@ -1306,15 +1348,17 @@ static inline void slab_free_freelist_hook(struct kmem_cache *s,
 #endif
 }
 
-static void setup_object(struct kmem_cache *s, struct page *page,
+static void *setup_object(struct kmem_cache *s, struct page *page,
 				void *object)
 {
-	setup_object_debug(s, page, object);
+	object = setup_object_debug(s, page, object);
 	if (unlikely(s->ctor)) {
 		kasan_unpoison_object_data(s, object);
 		s->ctor(object);
 		kasan_poison_object_data(s, object);
 	}
+
+	return object;
 }
 
 /*
@@ -1410,14 +1454,16 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
 	kasan_poison_slab(page);
 
 	for_each_object_idx(p, idx, s, start, page->objects) {
-		setup_object(s, page, p);
-		if (likely(idx < page->objects))
-			set_freepointer(s, p, p + s->size);
-		else
-			set_freepointer(s, p, NULL);
+		void *object = setup_object(s, page, p);
+
+		if (likely(idx < page->objects)) {
+			set_freepointer(s, object,
+				fixup_red_left(s, p + s->size));
+		} else
+			set_freepointer(s, object, NULL);
 	}
 
-	page->freelist = start;
+	page->freelist = fixup_red_left(s, start);
 	page->inuse = page->objects;
 	page->frozen = 1;
 
@@ -1458,8 +1504,11 @@ static void __free_slab(struct kmem_cache *s, struct page *page)
 
 		slab_pad_check(s, page);
 		for_each_object(p, s, page_address(page),
-						page->objects)
-			check_object(s, page, p, SLUB_RED_INACTIVE);
+						page->objects) {
+			void *object = fixup_red_left(s, p);
+
+			check_object(s, page, object, SLUB_RED_INACTIVE);
+		}
 	}
 
 	kmemcheck_free_shadow(page, compound_order(page));
@@ -3256,6 +3305,16 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
 		 * of the object.
 		 */
 		size += sizeof(void *);
+
+	if (flags & SLAB_RED_ZONE) {
+		s->red_left_pad = sizeof(void *);
+#ifdef CONFIG_KASAN
+		s->red_left_pad = min_t(int, s->red_left_pad,
+				KASAN_SHADOW_SCALE_SIZE);
+#endif
+		s->red_left_pad = ALIGN(s->red_left_pad, s->align);
+		size += s->red_left_pad;
+	}
 #endif
 
 	/*
@@ -3392,10 +3451,12 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
 
 	get_map(s, page, map);
 	for_each_object(p, s, addr, page->objects) {
+		void *object = fixup_red_left(s, p);
 
 		if (!test_bit(slab_index(p, s, addr), map)) {
-			pr_err("INFO: Object 0x%p @offset=%tu\n", p, p - addr);
-			print_tracking(s, p);
+			pr_err("INFO: Object 0x%p @offset=%tu\n",
+					object, object - addr);
+			print_tracking(s, object);
 		}
 	}
 	slab_unlock(page);
@@ -4064,15 +4125,21 @@ static int validate_slab(struct kmem_cache *s, struct page *page,
 
 	get_map(s, page, map);
 	for_each_object(p, s, addr, page->objects) {
+		void *object = fixup_red_left(s, p);
+
 		if (test_bit(slab_index(p, s, addr), map))
-			if (!check_object(s, page, p, SLUB_RED_INACTIVE))
+			if (!check_object(s, page, object, SLUB_RED_INACTIVE))
 				return 0;
 	}
 
-	for_each_object(p, s, addr, page->objects)
+	for_each_object(p, s, addr, page->objects) {
+		void *object = fixup_red_left(s, p);
+
 		if (!test_bit(slab_index(p, s, addr), map))
-			if (!check_object(s, page, p, SLUB_RED_ACTIVE))
+			if (!check_object(s, page, object, SLUB_RED_ACTIVE))
 				return 0;
+	}
+
 	return 1;
 }
 
@@ -4270,9 +4337,12 @@ static void process_slab(struct loc_track *t, struct kmem_cache *s,
 	bitmap_zero(map, page->objects);
 	get_map(s, page, map);
 
-	for_each_object(p, s, addr, page->objects)
+	for_each_object(p, s, addr, page->objects) {
+		void *object = fixup_red_left(s, p);
+
 		if (!test_bit(slab_index(p, s, addr), map))
-			add_location(t, s, get_track(s, p, alloc));
+			add_location(t, s, get_track(s, object, alloc));
+	}
 }
 
 static int list_locations(struct kmem_cache *s, char *buf,
-- 
1.9.1

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