On Wed, Jan 27, 2016 at 07:25:13PM +0100, Alexander Potapenko wrote:
> Quarantine isolates freed objects in a separate queue. The objects are
> returned to the allocator later, which helps to detect use-after-free
> errors.
>
> Freed objects are first added to per-cpu quarantine queues.
> When a cache is destroyed or memory shrinking is requested, the objects
> are moved into the global quarantine queue. Whenever a kmalloc call
> allows memory reclaiming, the oldest objects are popped out of the
> global queue until the total size of objects in quarantine is less than
> 3/4 of the maximum quarantine size (which is a fraction of installed
> physical memory).
Just wondering why not using time based approach rather than size
based one. In heavy load condition, how much time do the object stay in
quarantine?
>
> Right now quarantine support is only enabled in SLAB allocator.
> Unification of KASAN features in SLAB and SLUB will be done later.
>
> This patch is based on the "mm: kasan: quarantine" patch originally
> prepared by Dmitry Chernenkov.
>
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> ---
> include/linux/kasan.h | 30 ++++--
> lib/test_kasan.c | 29 ++++++
> mm/kasan/Makefile | 2 +-
> mm/kasan/kasan.c | 68 +++++++++++-
> mm/kasan/kasan.h | 11 +-
> mm/kasan/quarantine.c | 284 ++++++++++++++++++++++++++++++++++++++++++++++++++
> mm/kasan/report.c | 3 +-
> mm/mempool.c | 7 +-
> mm/page_alloc.c | 2 +-
> mm/slab.c | 12 ++-
> mm/slab.h | 4 +
> mm/slab_common.c | 2 +
> mm/slub.c | 4 +-
> 13 files changed, 435 insertions(+), 23 deletions(-)
>
...
> +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);
> +
> + switch (alloc_info->state) {
> + case KASAN_STATE_ALLOC:
> + alloc_info->state = KASAN_STATE_QUARANTINE;
> + quarantine_put(free_info, cache);
quarantine_put() can be called regardless of SLAB_DESTROY_BY_RCU,
although it's not much meaningful without poisoning. But, I have an
idea to poison object on SLAB_DESTROY_BY_RCU cache.
quarantine_put() moves per cpu list to global queue when
list size reaches QUARANTINE_PERCPU_SIZE. If we call synchronize_rcu()
at that time, after then, we can poison objects. With appropriate size
setup, it would not be intrusive.
> + set_track(&free_info->track, GFP_NOWAIT);
set_track() can be called regardless of SLAB_DESTROY_BY_RCU.
> + kasan_poison_slab_free(cache, object);
> + return true;
> + case KASAN_STATE_QUARANTINE:
> + case KASAN_STATE_FREE:
> + pr_err("Double free");
> + dump_stack();
> + break;
> + default:
> + break;
> + }
> + }
> + return false;
> +#else
> + kasan_poison_slab_free(cache, object);
> + return false;
> +#endif
> +}
> +
...
> +void quarantine_reduce(void)
> +{
> + size_t new_quarantine_size;
> + unsigned long flags;
> + struct qlist to_free = QLIST_INIT;
> + size_t size_to_free = 0;
> + void **last;
> +
> + if (likely(ACCESS_ONCE(global_quarantine.bytes) <=
> + smp_load_acquire(&quarantine_size)))
> + return;
> +
> + spin_lock_irqsave(&quarantine_lock, flags);
> +
> + /* Update quarantine size in case of hotplug. Allocate a fraction of
> + * the installed memory to quarantine minus per-cpu queue limits.
> + */
> + new_quarantine_size = (ACCESS_ONCE(totalram_pages) << PAGE_SHIFT) /
> + QUARANTINE_FRACTION;
> + new_quarantine_size -= QUARANTINE_PERCPU_SIZE * num_online_cpus();
> + smp_store_release(&quarantine_size, new_quarantine_size);
> +
> + last = global_quarantine.head;
> + while (last) {
> + struct kmem_cache *cache = qlink_to_cache(last);
> +
> + size_to_free += cache->size;
> + if (!*last || size_to_free >
> + global_quarantine.bytes - QUARANTINE_LOW_SIZE)
> + break;
> + last = (void **) *last;
> + }
> + qlist_move(&global_quarantine, last, &to_free, size_to_free);
> +
> + spin_unlock_irqrestore(&quarantine_lock, flags);
> +
> + qlist_free_all(&to_free, NULL);
> +}
Isn't it better to call quarantine_reduce() in shrink_slab()?
It will help to maximize quarantine time.
> +
> +static inline void qlist_move_cache(struct qlist *from,
> + struct qlist *to,
> + struct kmem_cache *cache)
> +{
> + void ***prev;
> +
> + if (unlikely(empty_qlist(from)))
> + return;
> +
> + prev = &from->head;
> + while (*prev) {
> + void **qlink = *prev;
> + struct kmem_cache *obj_cache = qlink_to_cache(qlink);
> +
> + if (obj_cache == cache) {
> + if (unlikely(from->tail == qlink))
> + from->tail = (void **) prev;
> + *prev = (void **) *qlink;
> + from->bytes -= cache->size;
> + qlist_put(to, qlink, cache->size);
> + } else
> + prev = (void ***) *prev;
> + }
> +}
> +
> +static void per_cpu_remove_cache(void *arg)
> +{
> + struct kmem_cache *cache = arg;
> + struct qlist to_free = QLIST_INIT;
> + struct qlist *q;
> + unsigned long flags;
> +
> + local_irq_save(flags);
> + q = this_cpu_ptr(&cpu_quarantine);
> + qlist_move_cache(q, &to_free, cache);
> + local_irq_restore(flags);
> +
> + qlist_free_all(&to_free, cache);
> +}
> +
> +void quarantine_remove_cache(struct kmem_cache *cache)
> +{
> + unsigned long flags;
> + struct qlist to_free = QLIST_INIT;
> +
> + on_each_cpu(per_cpu_remove_cache, cache, 0);
Should be called with wait = 1.
> +
> + spin_lock_irqsave(&quarantine_lock, flags);
> + qlist_move_cache(&global_quarantine, &to_free, cache);
> + spin_unlock_irqrestore(&quarantine_lock, flags);
> +
> + qlist_free_all(&to_free, cache);
> +}
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 6c4afcd..a4dca25 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -148,7 +148,8 @@ static void print_object(struct kmem_cache *cache, void *object)
> print_track(&alloc_info->track);
> break;
> case KASAN_STATE_FREE:
> - pr_err("Object freed, allocated with size %u bytes\n",
> + case KASAN_STATE_QUARANTINE:
> + pr_err("Object freed, allocated with size %lu bytes\n",
> alloc_info->alloc_size);
> free_info = get_free_info(cache, object);
> pr_err("Allocation:\n");
> diff --git a/mm/mempool.c b/mm/mempool.c
> index b47c8a7..4beeeef 100644
> --- a/mm/mempool.c
> +++ b/mm/mempool.c
> @@ -105,11 +105,12 @@ static inline void poison_element(mempool_t *pool, void *element)
> static void kasan_poison_element(mempool_t *pool, void *element)
> {
> if (pool->alloc == mempool_alloc_slab)
> - kasan_slab_free(pool->pool_data, element);
> + kasan_poison_slab_free(pool->pool_data, element);
> if (pool->alloc == mempool_kmalloc)
> - kasan_kfree(element);
> + kasan_poison_kfree(element);
> if (pool->alloc == mempool_alloc_pages)
> - kasan_free_pages(element, (unsigned long)pool->pool_data);
> + kasan_poison_free_pages(element,
> + (unsigned long)pool->pool_data);
> }
>
> static void kasan_unpoison_element(mempool_t *pool, void *element, gfp_t flags)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 63358d9..4f65587 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -980,7 +980,7 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
>
> trace_mm_page_free(page, order);
> kmemcheck_free_shadow(page, order);
> - kasan_free_pages(page, order);
> + kasan_poison_free_pages(page, order);
>
> if (PageAnon(page))
> page->mapping = NULL;
> diff --git a/mm/slab.c b/mm/slab.c
> index 0ec7aa3..e2fac67 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3374,9 +3374,19 @@ free_done:
> static inline void __cache_free(struct kmem_cache *cachep, void *objp,
> unsigned long caller)
> {
> +#ifdef CONFIG_KASAN
> + if (!kasan_slab_free(cachep, objp))
> + /* The object has been put into the quarantine, don't touch it
> + * for now.
> + */
> + nokasan_free(cachep, objp, caller);
> +}
> +
> +void nokasan_free(struct kmem_cache *cachep, void *objp, unsigned long caller)
> +{
> +#endif
It looks not good to me.
Converting __cache_free() to ____cache_free() and making
__cache_free() call ____cache_free() if (!kasan_slab_free()) looks
better to me and less error-prone.
Thanks.
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