From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
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 <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: <linux-mm@xxxxxxxxx>
Reported-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
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
