From: "Paul E. McKenney" <[email protected]> NULL pointers can be useful, but the NULL pointers from kmem_last_alloc() might be caused by any number of things: A not-to-a-slab pointer, failure to enable all the needed debugging, and bogus slob block-address computations. This commit therefore introduces error codes to the kmem_last_alloc() function using the ERR_PTR() facility, and also introduces kmem_last_alloc_errstring(), which translates the error codes into strings.
Cc: Christoph Lameter <[email protected]> Cc: Pekka Enberg <[email protected]> Cc: David Rientjes <[email protected]> Cc: Joonsoo Kim <[email protected]> Cc: Andrew Morton <[email protected]> Cc: <[email protected]> Reported-by: Andrii Nakryiko <[email protected]> Signed-off-by: Paul E. McKenney <[email protected]> --- include/linux/slab.h | 10 ++++++++++ mm/slab.c | 2 +- mm/slab_common.c | 28 ++++++++++++++++++++++++++-- mm/slob.c | 2 +- mm/slub.c | 4 ++-- 5 files changed, 40 insertions(+), 6 deletions(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index 06dd56b..031e630 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -133,6 +133,15 @@ #define ZERO_OR_NULL_PTR(x) ((unsigned long)(x) <= \ (unsigned long)ZERO_SIZE_PTR) +/* + * kmem_last_alloc error codes. + */ +#define KMEM_LA_NO_PAGE 1 /* No page structure for pointer. */ +#define KMEM_LA_NO_SLAB 2 /* Pointer not from slab allocator. */ +#define KMEM_LA_SLOB 3 /* No debugging info for slob. */ +#define KMEM_LA_NO_DEBUG 4 /* Debugging not enabled for slab/slub. */ +#define KMEM_LA_INCONSISTENT 5 /* Bogus block within slub page. */ + #include <linux/kasan.h> struct mem_cgroup; @@ -188,6 +197,7 @@ size_t __ksize(const void *); size_t ksize(const void *); void *kmem_cache_last_alloc(struct kmem_cache *s, void *object); void *kmem_last_alloc(void *object); +const char *kmem_last_alloc_errstring(void *lastalloc); #ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR void __check_heap_object(const void *ptr, unsigned long n, struct page *page, diff --git a/mm/slab.c b/mm/slab.c index 2ab93b8..1f3b263 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3610,7 +3610,7 @@ void *kmem_cache_last_alloc(struct kmem_cache *cachep, void *object) struct page *page; if (!(cachep->flags & SLAB_STORE_USER)) - return NULL; + return ERR_PTR(-KMEM_LA_NO_DEBUG); objp = object - obj_offset(cachep); page = virt_to_head_page(objp); objnr = obj_to_index(cachep, page, objp); diff --git a/mm/slab_common.c b/mm/slab_common.c index 3f647982..8430a14 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -537,6 +537,30 @@ bool slab_is_available(void) } /* + * If the pointer corresponds to a kmem_last_alloc() error, return + * a pointer to the corresponding string, otherwise NULL. + */ +const char *kmem_last_alloc_errstring(void *lastalloc) +{ + long klaerrno; + static const char * const es[] = { + "local memory", /* KMEM_LA_NO_PAGE - 1 */ + "non-slab memory", /* KMEM_LA_NO_SLAB - 1 */ + "slob doesn't do debug", /* KMEM_LA_SLOB - 1 */ + "debugging disabled", /* KMEM_LA_NO_DEBUG - 1 */ + "bogus slub block", /* KMEM_LA_INCONSISTENT - 1 */ + }; + + if (!IS_ERR(lastalloc)) + return NULL; + klaerrno = -PTR_ERR(lastalloc) - 1; + if (WARN_ON_ONCE(klaerrno >= ARRAY_SIZE(es))) + return "kmem_last_alloc error out of range"; + return es[klaerrno]; +} +EXPORT_SYMBOL_GPL(kmem_last_alloc_errstring); + +/* * If the pointer references a slab-allocated object and if sufficient * debugging is enabled, return the returrn address for the corresponding * allocation. Otherwise, return NULL. Note that passing random pointers @@ -548,10 +572,10 @@ void *kmem_last_alloc(void *object) struct page *page; if (!virt_addr_valid(object)) - return NULL; + return ERR_PTR(-KMEM_LA_NO_PAGE); page = virt_to_head_page(object); if (!PageSlab(page)) - return NULL; + return ERR_PTR(-KMEM_LA_NO_SLAB); return kmem_cache_last_alloc(page->slab_cache, object); } EXPORT_SYMBOL_GPL(kmem_last_alloc); diff --git a/mm/slob.c b/mm/slob.c index c1f8ed7..e7d6b90 100644 --- a/mm/slob.c +++ b/mm/slob.c @@ -463,7 +463,7 @@ static void slob_free(void *block, int size) void *kmem_cache_last_alloc(struct kmem_cache *s, void *object) { - return NULL; + return ERR_PTR(-KMEM_LA_SLOB); } /* diff --git a/mm/slub.c b/mm/slub.c index 8ed3ba2..3ddf16a 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3928,7 +3928,7 @@ void *kmem_cache_last_alloc(struct kmem_cache *s, void *object) struct track *trackp; if (!(s->flags & SLAB_STORE_USER)) - return NULL; + return ERR_PTR(-KMEM_LA_NO_DEBUG); page = virt_to_head_page(object); base = page_address(page); objp = kasan_reset_tag(object); @@ -3936,7 +3936,7 @@ void *kmem_cache_last_alloc(struct kmem_cache *s, void *object) objnr = obj_to_index(s, page, objp); objp = base + s->size * objnr; if (objp < base || objp >= base + page->objects * s->size || (objp - base) % s->size) - return NULL; + return ERR_PTR(-KMEM_LA_INCONSISTENT); trackp = get_track(s, objp, TRACK_ALLOC); return (void *)trackp->addr; #else -- 2.9.5
