From: David Rientjes rientjes@google.com
Mempools keep elements in a reserved pool for contexts in which allocation may not be possible. When an element is allocated from the reserved pool, its memory contents is the same as when it was added to the reserved pool.
Because of this, elements lack any free poisoning to detect use-after-free errors.
This patch adds free poisoning for elements backed by the slab allocator. This is possible because the mempool layer knows the object size of each element.
When an element is added to the reserved pool, it is poisoned with POISON_FREE. When it is removed from the reserved pool, the contents are checked for POISON_FREE. If there is a mismatch, a warning is emitted to the kernel log.
This is only effective for configs with CONFIG_DEBUG_SLAB or CONFIG_SLUB_DEBUG_ON.
[fabio.estevam@freescale.com: use '%zu' for printing 'size_t' variable] [arnd@arndb.de: add missing include] Signed-off-by: David Rientjes rientjes@google.com Cc: Dave Kleikamp shaggy@kernel.org Cc: Christoph Hellwig hch@lst.de Cc: Sebastian Ott sebott@linux.vnet.ibm.com Cc: Mikulas Patocka mpatocka@redhat.com Cc: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Fabio Estevam fabio.estevam@freescale.com Signed-off-by: Arnd Bergmann arnd@arndb.de Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org
(cherry picked from commit bdfedb76f4f5aa5e37380e3b71adee4a39f30fc6) Signed-off-by: Alex Shi alex.shi@linaro.org --- mm/mempool.c | 92 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 90 insertions(+), 2 deletions(-)
diff --git a/mm/mempool.c b/mm/mempool.c index b60fb85..2884d5b 100644 --- a/mm/mempool.c +++ b/mm/mempool.c @@ -6,10 +6,12 @@ * extreme VM load. * * started by Ingo Molnar, Copyright (C) 2001 + * debugging by David Rientjes, Copyright (C) 2015 */
#include <linux/mm.h> #include <linux/slab.h> +#include <linux/highmem.h> #include <linux/kmemleak.h> #include <linux/export.h> #include <linux/mempool.h> @@ -17,16 +19,102 @@ #include <linux/writeback.h> #include "slab.h"
+#if defined(CONFIG_DEBUG_SLAB) || defined(CONFIG_SLUB_DEBUG_ON) +static void poison_error(mempool_t *pool, void *element, size_t size, + size_t byte) +{ + const int nr = pool->curr_nr; + const int start = max_t(int, byte - (BITS_PER_LONG / 8), 0); + const int end = min_t(int, byte + (BITS_PER_LONG / 8), size); + int i; + + pr_err("BUG: mempool element poison mismatch\n"); + pr_err("Mempool %p size %zu\n", pool, size); + pr_err(" nr=%d @ %p: %s0x", nr, element, start > 0 ? "... " : ""); + for (i = start; i < end; i++) + pr_cont("%x ", *(u8 *)(element + i)); + pr_cont("%s\n", end < size ? "..." : ""); + dump_stack(); +} + +static void __check_element(mempool_t *pool, void *element, size_t size) +{ + u8 *obj = element; + size_t i; + + for (i = 0; i < size; i++) { + u8 exp = (i < size - 1) ? POISON_FREE : POISON_END; + + if (obj[i] != exp) { + poison_error(pool, element, size, i); + return; + } + } + memset(obj, POISON_INUSE, size); +} + +static void check_element(mempool_t *pool, void *element) +{ + /* Mempools backed by slab allocator */ + if (pool->free == mempool_free_slab || pool->free == mempool_kfree) + __check_element(pool, element, ksize(element)); + + /* Mempools backed by page allocator */ + if (pool->free == mempool_free_pages) { + int order = (int)(long)pool->pool_data; + void *addr = kmap_atomic((struct page *)element); + + __check_element(pool, addr, 1UL << (PAGE_SHIFT + order)); + kunmap_atomic(addr); + } +} + +static void __poison_element(void *element, size_t size) +{ + u8 *obj = element; + + memset(obj, POISON_FREE, size - 1); + obj[size - 1] = POISON_END; +} + +static void poison_element(mempool_t *pool, void *element) +{ + /* Mempools backed by slab allocator */ + if (pool->alloc == mempool_alloc_slab || pool->alloc == mempool_kmalloc) + __poison_element(element, ksize(element)); + + /* Mempools backed by page allocator */ + if (pool->alloc == mempool_alloc_pages) { + int order = (int)(long)pool->pool_data; + void *addr = kmap_atomic((struct page *)element); + + __poison_element(addr, 1UL << (PAGE_SHIFT + order)); + kunmap_atomic(addr); + } +} +#else /* CONFIG_DEBUG_SLAB || CONFIG_SLUB_DEBUG_ON */ +static inline void check_element(mempool_t *pool, void *element) +{ +} +static inline void poison_element(mempool_t *pool, void *element) +{ +} +#endif /* CONFIG_DEBUG_SLAB || CONFIG_SLUB_DEBUG_ON */ + static void add_element(mempool_t *pool, void *element) { BUG_ON(pool->curr_nr >= pool->min_nr); + poison_element(pool, element); pool->elements[pool->curr_nr++] = element; }
static void *remove_element(mempool_t *pool) { - BUG_ON(pool->curr_nr <= 0); - return pool->elements[--pool->curr_nr]; + void *element = pool->elements[--pool->curr_nr]; + + BUG_ON(pool->curr_nr < 0); + check_element(pool, element); + return element; }
/**