Messages in this thread Patch in this message |  | | From | Dmitry Vyukov <> | Subject | [PATCH] lib: bump stackdepot capacity from 16MB to 128MB | Date | Fri, 14 Oct 2016 17:20:16 +0200 |
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KASAN uses stackdepot to memorize stacks for all kmalloc/kfree calls. Current stackdepot capacity is 16MB (1024 top level entries x 4 pages on second level). Size of each stack is (num_frames + 3) * sizeof(long). Which gives us ~84K stacks. This capacity was chosen empirically and it is enough to run kernel normally. However, when lots of configs are enabled and a fuzzer tries to maximize code coverage, it easily hits the limit within tens of minutes. I've tested for long a time with number of top level entries bumped 4x (4096). And I think I've seen overflow only once. But I don't have all configs enabled and code coverage has not reached maximum yet. So bump it 8x to 8192. Since we have two-level table, memory cost of this is very moderate -- currently the top-level table is 8KB, with this patch it is 64KB, which is negligible under KASAN.
Here is some approx math. 128MB allows us to memorize ~670K stacks (assuming stack is ~200b). I've grepped kernel for kmalloc|kfree|kmem_cache_alloc|kmem_cache_free| kzalloc|kstrdup|kstrndup|kmemdup and it gives ~60K matches. Most of alloc/free call sites are reachable with only one stack. But some utility functions can have large fanout. Assuming average fanout is 5x, total number of alloc/free stacks is ~300K.
Signed-off-by: Dmitry Vyukov <dvyukov@google.com> Cc: kasan-dev@googlegroups.com Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Alexander Potapenko <glider@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: sploving1@gmail.com Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org --- lib/stackdepot.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lib/stackdepot.c b/lib/stackdepot.c index 60f77f1..4d830e2 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -50,7 +50,7 @@ STACK_ALLOC_ALIGN) #define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - \ STACK_ALLOC_NULL_PROTECTION_BITS - STACK_ALLOC_OFFSET_BITS) -#define STACK_ALLOC_SLABS_CAP 1024 +#define STACK_ALLOC_SLABS_CAP 8192 #define STACK_ALLOC_MAX_SLABS \ (((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \ (1LL << (STACK_ALLOC_INDEX_BITS)) : STACK_ALLOC_SLABS_CAP) -- 2.8.0.rc3.226.g39d4020
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