Re: [PATCH v5] mm, kasan: switch SLUB to stackdepot, enable memory quarantine for SLUB
From: Andrey Ryabinin
Date: Tue Jun 28 2016 - 13:06:22 EST
On 06/22/2016 08:43 PM, Alexander Potapenko wrote:
> For KASAN builds:
> - switch SLUB allocator to using stackdepot instead of storing the
> allocation/deallocation stacks in the objects;
> - change the freelist hook so that parts of the freelist can be put
> into the quarantine.
>
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> ---
> v5: - addressed comments by Andrey Ryabinin:
> - don't define SLAB_RED_ZONE, SLAB_POISON, SLAB_STORE_USER to 0
check_pad_bytes() needs fixing. It should take into accout kasan metadata size.
> - account for left redzone size when SLAB_RED_ZONE is used
> - incidentally moved the implementations of nearest_obj() to mm/sl[au]b.c
> v4: - addressed comments by Andrey Ryabinin:
> - don't set slub_debug by default for everyone;
> - introduce the ___cache_free() helper function.
> v3: - addressed comments by Andrey Ryabinin:
> - replaced KMALLOC_MAX_CACHE_SIZE with KMALLOC_MAX_SIZE in
> kasan_cache_create();
> - for caches with SLAB_KASAN flag set, their alloc_meta_offset and
> free_meta_offset are always valid.
> v2: - incorporated kbuild fixes by Andrew Morton
> ---
> include/linux/slab_def.h | 11 -------
> include/linux/slub_def.h | 15 +++-------
> lib/Kconfig.kasan | 4 +--
> mm/kasan/Makefile | 3 +-
> mm/kasan/kasan.c | 61 ++++++++++++++++++++------------------
> mm/kasan/kasan.h | 2 +-
> mm/kasan/report.c | 8 ++---
> mm/slab.c | 11 +++++++
> mm/slab.h | 9 ++++++
> mm/slub.c | 76 +++++++++++++++++++++++++++++++++++++++---------
> 10 files changed, 126 insertions(+), 74 deletions(-)
>
> diff --git a/include/linux/slab_def.h b/include/linux/slab_def.h
> index 8694f7a..a20e11c 100644
> --- a/include/linux/slab_def.h
> +++ b/include/linux/slab_def.h
> @@ -87,15 +87,4 @@ struct kmem_cache {
> struct kmem_cache_node *node[MAX_NUMNODES];
> };
>
> -static inline void *nearest_obj(struct kmem_cache *cache, struct page *page,
> - void *x) {
> - void *object = x - (x - page->s_mem) % cache->size;
> - void *last_object = page->s_mem + (cache->num - 1) * cache->size;
> -
> - if (unlikely(object > last_object))
> - return last_object;
> - else
> - return object;
> -}
> -
> #endif /* _LINUX_SLAB_DEF_H */
> diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
> index d1faa01..da80e7f 100644
> --- a/include/linux/slub_def.h
> +++ b/include/linux/slub_def.h
> @@ -99,6 +99,10 @@ struct kmem_cache {
> */
> int remote_node_defrag_ratio;
> #endif
> +#ifdef CONFIG_KASAN
> + struct kasan_cache kasan_info;
> +#endif
> +
> struct kmem_cache_node *node[MAX_NUMNODES];
> };
>
> @@ -114,15 +118,4 @@ static inline void sysfs_slab_remove(struct kmem_cache *s)
> void object_err(struct kmem_cache *s, struct page *page,
> u8 *object, char *reason);
>
> -static inline void *nearest_obj(struct kmem_cache *cache, struct page *page,
> - void *x) {
> - void *object = x - (x - page_address(page)) % cache->size;
> - void *last_object = page_address(page) +
> - (page->objects - 1) * cache->size;
> - if (unlikely(object > last_object))
> - return last_object;
> - else
> - return object;
> -}
> -
> #endif /* _LINUX_SLUB_DEF_H */
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index 67d8c68..bd38aab 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -5,9 +5,9 @@ if HAVE_ARCH_KASAN
>
> config KASAN
> bool "KASan: runtime memory debugger"
> - depends on SLUB_DEBUG || (SLAB && !DEBUG_SLAB)
> + depends on SLUB || (SLAB && !DEBUG_SLAB)
> select CONSTRUCTORS
> - select STACKDEPOT if SLAB
> + select STACKDEPOT
> help
> Enables kernel address sanitizer - runtime memory debugger,
> designed to find out-of-bounds accesses and use-after-free bugs.
> diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
> index 1548749..2976a9e 100644
> --- a/mm/kasan/Makefile
> +++ b/mm/kasan/Makefile
> @@ -7,5 +7,4 @@ CFLAGS_REMOVE_kasan.o = -pg
> # see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
> CFLAGS_kasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
>
> -obj-y := kasan.o report.o kasan_init.o
> -obj-$(CONFIG_SLAB) += quarantine.o
> +obj-y := kasan.o report.o kasan_init.o quarantine.o
> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
> index 28439ac..3883e22 100644
> --- a/mm/kasan/kasan.c
> +++ b/mm/kasan/kasan.c
> @@ -351,7 +351,6 @@ void kasan_free_pages(struct page *page, unsigned int order)
> KASAN_FREE_PAGE);
> }
>
> -#ifdef CONFIG_SLAB
> /*
> * Adaptive redzone policy taken from the userspace AddressSanitizer runtime.
> * For larger allocations larger redzones are used.
> @@ -373,16 +372,12 @@ void kasan_cache_create(struct kmem_cache *cache, size_t *size,
> unsigned long *flags)
> {
> int redzone_adjust;
> - /* Make sure the adjusted size is still less than
> - * KMALLOC_MAX_CACHE_SIZE.
> - * TODO: this check is only useful for SLAB, but not SLUB. We'll need
> - * to skip it for SLUB when it starts using kasan_cache_create().
> - */
> - if (*size > KMALLOC_MAX_CACHE_SIZE -
> - sizeof(struct kasan_alloc_meta) -
> - sizeof(struct kasan_free_meta))
> - return;
> +#ifdef CONFIG_SLAB
> + int orig_size = *size;
> +#endif
> +
> *flags |= SLAB_KASAN;
> +
> /* Add alloc meta. */
> cache->kasan_info.alloc_meta_offset = *size;
> *size += sizeof(struct kasan_alloc_meta);
> @@ -392,17 +387,35 @@ void kasan_cache_create(struct kmem_cache *cache, size_t *size,
> cache->object_size < sizeof(struct kasan_free_meta)) {
> cache->kasan_info.free_meta_offset = *size;
> *size += sizeof(struct kasan_free_meta);
> + } else {
> + cache->kasan_info.free_meta_offset = 0;
Why is that required now?
> }
> redzone_adjust = optimal_redzone(cache->object_size) -
> (*size - cache->object_size);
> +
> if (redzone_adjust > 0)
> *size += redzone_adjust;
> - *size = min(KMALLOC_MAX_CACHE_SIZE,
> +
> +#ifdef CONFIG_SLAB
> + *size = min(KMALLOC_MAX_SIZE,
> max(*size,
> cache->object_size +
> optimal_redzone(cache->object_size)));
> -}
> + /*
> + * If the metadata doesn't fit, disable KASAN at all.
> + */
> + if (*size <= cache->kasan_info.alloc_meta_offset ||
> + *size <= cache->kasan_info.free_meta_offset) {
> + *flags &= ~SLAB_KASAN;
Why we change that flag back and forth instead of setting it once?
> + *size = orig_size;
> + }
> +#else
> + *size = max(*size,
> + cache->object_size +
> + optimal_redzone(cache->object_size));
> +
> #endif
> +}
>
> void kasan_cache_shrink(struct kmem_cache *cache)
> {
> @@ -431,16 +444,13 @@ void kasan_poison_object_data(struct kmem_cache *cache, void *object)
> kasan_poison_shadow(object,
> round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE),
> KASAN_KMALLOC_REDZONE);
> -#ifdef CONFIG_SLAB
> if (cache->flags & SLAB_KASAN) {
> struct kasan_alloc_meta *alloc_info =
> get_alloc_info(cache, object);
> alloc_info->state = KASAN_STATE_INIT;
> }
> -#endif
> }
>
> -#ifdef CONFIG_SLAB
> static inline int in_irqentry_text(unsigned long ptr)
> {
> return (ptr >= (unsigned long)&__irqentry_text_start &&
> @@ -501,7 +511,6 @@ struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
> BUILD_BUG_ON(sizeof(struct kasan_free_meta) > 32);
> return (void *)object + cache->kasan_info.free_meta_offset;
> }
> -#endif
>
> void kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
> {
> @@ -522,16 +531,16 @@ void kasan_poison_slab_free(struct kmem_cache *cache, void *object)
>
> bool kasan_slab_free(struct kmem_cache *cache, void *object)
> {
> -#ifdef CONFIG_SLAB
> /* RCU slabs could be legally used after free within the RCU period */
> if (unlikely(cache->flags & SLAB_DESTROY_BY_RCU))
> return false;
>
> if (likely(cache->flags & SLAB_KASAN)) {
> - struct kasan_alloc_meta *alloc_info =
> - get_alloc_info(cache, object);
> - struct kasan_free_meta *free_info =
> - get_free_info(cache, object);
> + struct kasan_alloc_meta *alloc_info;
> + struct kasan_free_meta *free_info;
> +
> + alloc_info = get_alloc_info(cache, object);
> + free_info = get_free_info(cache, object);
>
> switch (alloc_info->state) {
> case KASAN_STATE_ALLOC:
> @@ -550,10 +559,6 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object)
> }
> }
> return false;
> -#else
> - kasan_poison_slab_free(cache, object);
> - return false;
> -#endif
> }
>
> void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
> @@ -568,6 +573,9 @@ void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
> if (unlikely(object == NULL))
> return;
>
> + if (!(cache->flags & SLAB_KASAN))
> + return;
> +
This hunk is superfluous and wrong.
> redzone_start = round_up((unsigned long)(object + size),
> KASAN_SHADOW_SCALE_SIZE);
> redzone_end = round_up((unsigned long)object + cache->object_size,
> @@ -576,16 +584,13 @@ void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
> kasan_unpoison_shadow(object, size);
> kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
> KASAN_KMALLOC_REDZONE);
> -#ifdef CONFIG_SLAB
> if (cache->flags & SLAB_KASAN) {
> struct kasan_alloc_meta *alloc_info =
> get_alloc_info(cache, object);
> -
Keep the space please.
> alloc_info->state = KASAN_STATE_ALLOC;
> alloc_info->alloc_size = size;
> set_track(&alloc_info->track, flags);
> }
> -#endif
> }
> EXPORT_SYMBOL(kasan_kmalloc);
>
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index fb87923..8c75953 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -110,7 +110,7 @@ static inline bool kasan_report_enabled(void)
> void kasan_report(unsigned long addr, size_t size,
> bool is_write, unsigned long ip);
>
> -#ifdef CONFIG_SLAB
> +#if defined(CONFIG_SLAB) || defined(CONFIG_SLUB)
> void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);
> void quarantine_reduce(void);
> void quarantine_remove_cache(struct kmem_cache *cache);
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index b3c122d..861b977 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -116,7 +116,6 @@ static inline bool init_task_stack_addr(const void *addr)
> sizeof(init_thread_union.stack));
> }
>
> -#ifdef CONFIG_SLAB
> static void print_track(struct kasan_track *track)
> {
> pr_err("PID = %u\n", track->pid);
> @@ -130,8 +129,8 @@ static void print_track(struct kasan_track *track)
> }
> }
>
> -static void object_err(struct kmem_cache *cache, struct page *page,
> - void *object, char *unused_reason)
> +static void kasan_object_err(struct kmem_cache *cache, struct page *page,
> + void *object, char *unused_reason)
> {
> struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
> struct kasan_free_meta *free_info;
> @@ -162,7 +161,6 @@ static void object_err(struct kmem_cache *cache, struct page *page,
> break;
> }
> }
> -#endif
>
> static void print_address_description(struct kasan_access_info *info)
> {
> @@ -177,7 +175,7 @@ static void print_address_description(struct kasan_access_info *info)
> struct kmem_cache *cache = page->slab_cache;
> object = nearest_obj(cache, page,
> (void *)info->access_addr);
> - object_err(cache, page, object,
> + kasan_object_err(cache, page, object,
> "kasan: bad access detected");
> return;
> }
> diff --git a/mm/slab.c b/mm/slab.c
> index cc8bbc1..e944171 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -4506,3 +4506,14 @@ size_t ksize(const void *objp)
> return size;
> }
> EXPORT_SYMBOL(ksize);
> +
> +void *nearest_obj(struct kmem_cache *cache, struct page *page, void *x)
> +{
> + void *object = x - (x - page->s_mem) % cache->size;
> + void *last_object = page->s_mem + (cache->num - 1) * cache->size;
> +
> + if (unlikely(object > last_object))
> + return last_object;
> + else
> + return object;
> +}
This should be in header. Don't bloat CONFIG_KASAN=n kernels.
> diff --git a/mm/slab.h b/mm/slab.h
> index dedb1a9..52edd1e 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -366,6 +366,8 @@ static inline size_t slab_ksize(const struct kmem_cache *s)
> if (s->flags & (SLAB_RED_ZONE | SLAB_POISON))
> return s->object_size;
> # endif
> + if (s->flags & SLAB_KASAN)
> + return s->object_size;
> /*
> * If we have the need to store the freelist pointer
> * back there or track user information then we can
> @@ -462,6 +464,13 @@ void *slab_next(struct seq_file *m, void *p, loff_t *pos);
> void slab_stop(struct seq_file *m, void *p);
> int memcg_slab_show(struct seq_file *m, void *p);
>
> +void *nearest_obj(struct kmem_cache *cache, struct page *page, void *x);
> +
> void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr);
> +#if defined(CONFIG_SLUB)
> +void do_slab_free(struct kmem_cache *s,
> + struct page *page, void *head, void *tail,
> + int cnt, unsigned long addr);
> +#endif
>
> #endif /* MM_SLAB_H */
> diff --git a/mm/slub.c b/mm/slub.c
> index 825ff45..3ef06e3 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -191,7 +191,11 @@ static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s)
> #define MAX_OBJS_PER_PAGE 32767 /* since page.objects is u15 */
>
> /* Internal SLUB flags */
> +#ifndef CONFIG_KASAN
> #define __OBJECT_POISON 0x80000000UL /* Poison object */
> +#else
> +#define __OBJECT_POISON 0x00000000UL /* Disable object poisoning */
Again, why? It should just work.
> +#endif
> #define __CMPXCHG_DOUBLE 0x40000000UL /* Use cmpxchg_double */
>
> #ifdef CONFIG_SMP
> @@ -454,8 +458,6 @@ static inline void *restore_red_left(struct kmem_cache *s, void *p)
> */
> #if defined(CONFIG_SLUB_DEBUG_ON)
> static int slub_debug = DEBUG_DEFAULT_FLAGS;
> -#elif defined(CONFIG_KASAN)
> -static int slub_debug = SLAB_STORE_USER;
> #else
> static int slub_debug;
> #endif
> @@ -1322,7 +1324,7 @@ static inline void kfree_hook(const void *x)
> kasan_kfree_large(x);
> }
>
> -static inline void slab_free_hook(struct kmem_cache *s, void *x)
> +static inline bool slab_free_hook(struct kmem_cache *s, void *x)
> {
> kmemleak_free_recursive(x, s->flags);
>
> @@ -1344,11 +1346,11 @@ static inline void slab_free_hook(struct kmem_cache *s, void *x)
> if (!(s->flags & SLAB_DEBUG_OBJECTS))
> debug_check_no_obj_freed(x, s->object_size);
>
> - kasan_slab_free(s, x);
> + return kasan_slab_free(s, x);
> }
>
> static inline void slab_free_freelist_hook(struct kmem_cache *s,
> - void *head, void *tail)
> + void **head, void **tail, int *cnt)
> {
> /*
> * Compiler cannot detect this function can be removed if slab_free_hook()
> @@ -1360,13 +1362,27 @@ static inline void slab_free_freelist_hook(struct kmem_cache *s,
> defined(CONFIG_DEBUG_OBJECTS_FREE) || \
> defined(CONFIG_KASAN)
>
> - void *object = head;
> - void *tail_obj = tail ? : head;
> + void *object = *head, *prev = NULL, *next = NULL;
> + void *tail_obj = *tail ? : *head;
> + bool skip = false;
>
> do {
> - slab_free_hook(s, object);
> - } while ((object != tail_obj) &&
> - (object = get_freepointer(s, object)));
> + skip = slab_free_hook(s, object);
> + next = (object != tail_obj) ?
> + get_freepointer(s, object) : NULL;
> + if (skip) {
> + if (!prev)
> + *head = next;
> + else
> + set_freepointer(s, prev, next);
> + if (object == tail_obj)
> + *tail = prev;
> + (*cnt)--;
> + } else {
> + prev = object;
> + }
> + object = next;
> + } while (next);
> #endif
> }
>
> @@ -2772,12 +2788,22 @@ static __always_inline void slab_free(struct kmem_cache *s, struct page *page,
> void *head, void *tail, int cnt,
> unsigned long addr)
> {
> + void *free_head = head, *free_tail = tail;
> +
> + slab_free_freelist_hook(s, &free_head, &free_tail, &cnt);
> + /* slab_free_freelist_hook() could have emptied the freelist. */
> + if (cnt == 0)
> + return;
I suppose that we can do something like following, instead of that mess in slab_free_freelist_hook() above
slab_free_freelist_hook(s, &free_head, &free_tail);
if (s->flags & SLAB_KASAN && s->flags & SLAB_DESTROY_BY_RCU)
return;
> + do_slab_free(s, page, free_head, free_tail, cnt, addr);
> +}
> +
> +__always_inline void do_slab_free(struct kmem_cache *s,
static
> + struct page *page, void *head, void *tail,
> + int cnt, unsigned long addr)
> +{
> void *tail_obj = tail ? : head;
> struct kmem_cache_cpu *c;
> unsigned long tid;
> -
> - slab_free_freelist_hook(s, head, tail);
> -
> redo:
> /*
> * Determine the currently cpus per cpu slab.
> @@ -2811,6 +2837,12 @@ redo:
>
> }
>
> +/* Helper function to be used from qlink_free() in mm/kasan/quarantine.c */
We have grep to locate all call sites. Unlike comments like this, grep results always uptodate.
> +void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr)
> +{
> + do_slab_free(cache, virt_to_head_page(x), x, NULL, 1, addr);
> +}
> +
> void kmem_cache_free(struct kmem_cache *s, void *x)
> {
> s = cache_from_obj(s, x);
> @@ -3252,7 +3284,7 @@ static void set_min_partial(struct kmem_cache *s, unsigned long min)
> static int calculate_sizes(struct kmem_cache *s, int forced_order)
> {
> unsigned long flags = s->flags;
> - unsigned long size = s->object_size;
> + size_t size = s->object_size;
> int order;
>
> /*
> @@ -3311,7 +3343,10 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
> * the object.
> */
> size += 2 * sizeof(struct track);
> +#endif
>
> + kasan_cache_create(s, &size, &s->flags);
> +#ifdef CONFIG_SLUB_DEBUG
> if (flags & SLAB_RED_ZONE) {
> /*
> * Add some empty padding so that we can catch
> @@ -5585,3 +5620,16 @@ ssize_t slabinfo_write(struct file *file, const char __user *buffer,
> return -EIO;
> }
> #endif /* CONFIG_SLABINFO */
> +
> +void *nearest_obj(struct kmem_cache *cache, struct page *page,
> + void *x) {
> + void *object = x - (x - page_address(page)) % cache->size;
> + void *last_object = page_address(page) +
> + (page->objects - 1) * cache->size;
> + void *result = (unlikely(object > last_object)) ? last_object : object;
> +
> + if (cache->flags & SLAB_RED_ZONE)
> + return (void *)((char *)result + cache->red_left_pad);
red_left_pad is zero when SLAB_RED_ZONE is unset, so if/else is not needed here.
And it can be moved back to header now.
Also, you don't need (void *) cast.
> + else
> + return result;
> +}
>