The patch titled
Subject: mm: SLUB freelist randomization
has been added to the -mm tree. Its filename is
mm-slub-freelist-randomization.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-slub-freelist-randomization.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-slub-freelist-randomization.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Thomas Garnier <thgarnie@xxxxxxxxxx>
Subject: mm: SLUB freelist randomization
Implements freelist randomization for the SLUB allocator. It was previous
implemented for the SLAB allocator. Both use the same configuration
option (CONFIG_SLAB_FREELIST_RANDOM).
The list is randomized during initialization of a new set of pages. The
order on different freelist sizes is pre-computed at boot for performance.
Each kmem_cache has its own randomized freelist. This security feature
reduces the predictability of the kernel SLUB allocator against heap
overflows rendering attacks much less stable.
For example these attacks exploit the predictability of the heap:
- Linux Kernel CAN SLUB overflow (https://goo.gl/oMNWkU)
- Exploiting Linux Kernel Heap corruptions (http://goo.gl/EXLn95)
Performance results:
slab_test impact is between 3% to 4% on average for 100000 attemps wihout
smp. It is a very focused testing, kernbench show the overall impact on
the system is way lower.
Before:
Single thread testing
=====================
1. Kmalloc: Repeatedly allocate then free test
100000 times kmalloc(8) -> 49 cycles kfree -> 77 cycles
100000 times kmalloc(16) -> 51 cycles kfree -> 79 cycles
100000 times kmalloc(32) -> 53 cycles kfree -> 83 cycles
100000 times kmalloc(64) -> 62 cycles kfree -> 90 cycles
100000 times kmalloc(128) -> 81 cycles kfree -> 97 cycles
100000 times kmalloc(256) -> 98 cycles kfree -> 121 cycles
100000 times kmalloc(512) -> 95 cycles kfree -> 122 cycles
100000 times kmalloc(1024) -> 96 cycles kfree -> 126 cycles
100000 times kmalloc(2048) -> 115 cycles kfree -> 140 cycles
100000 times kmalloc(4096) -> 149 cycles kfree -> 171 cycles
2. Kmalloc: alloc/free test
100000 times kmalloc(8)/kfree -> 70 cycles
100000 times kmalloc(16)/kfree -> 70 cycles
100000 times kmalloc(32)/kfree -> 70 cycles
100000 times kmalloc(64)/kfree -> 70 cycles
100000 times kmalloc(128)/kfree -> 70 cycles
100000 times kmalloc(256)/kfree -> 69 cycles
100000 times kmalloc(512)/kfree -> 70 cycles
100000 times kmalloc(1024)/kfree -> 73 cycles
100000 times kmalloc(2048)/kfree -> 72 cycles
100000 times kmalloc(4096)/kfree -> 71 cycles
After:
Single thread testing
=====================
1. Kmalloc: Repeatedly allocate then free test
100000 times kmalloc(8) -> 57 cycles kfree -> 78 cycles
100000 times kmalloc(16) -> 61 cycles kfree -> 81 cycles
100000 times kmalloc(32) -> 76 cycles kfree -> 93 cycles
100000 times kmalloc(64) -> 83 cycles kfree -> 94 cycles
100000 times kmalloc(128) -> 106 cycles kfree -> 107 cycles
100000 times kmalloc(256) -> 118 cycles kfree -> 117 cycles
100000 times kmalloc(512) -> 114 cycles kfree -> 116 cycles
100000 times kmalloc(1024) -> 115 cycles kfree -> 118 cycles
100000 times kmalloc(2048) -> 147 cycles kfree -> 131 cycles
100000 times kmalloc(4096) -> 214 cycles kfree -> 161 cycles
2. Kmalloc: alloc/free test
100000 times kmalloc(8)/kfree -> 66 cycles
100000 times kmalloc(16)/kfree -> 66 cycles
100000 times kmalloc(32)/kfree -> 66 cycles
100000 times kmalloc(64)/kfree -> 66 cycles
100000 times kmalloc(128)/kfree -> 65 cycles
100000 times kmalloc(256)/kfree -> 67 cycles
100000 times kmalloc(512)/kfree -> 67 cycles
100000 times kmalloc(1024)/kfree -> 64 cycles
100000 times kmalloc(2048)/kfree -> 67 cycles
100000 times kmalloc(4096)/kfree -> 67 cycles
Kernbench, before:
Average Optimal load -j 12 Run (std deviation):
Elapsed Time 101.873 (1.16069)
User Time 1045.22 (1.60447)
System Time 88.969 (0.559195)
Percent CPU 1112.9 (13.8279)
Context Switches 189140 (2282.15)
Sleeps 99008.6 (768.091)
After:
Average Optimal load -j 12 Run (std deviation):
Elapsed Time 102.47 (0.562732)
User Time 1045.3 (1.34263)
System Time 88.311 (0.342554)
Percent CPU 1105.8 (6.49444)
Context Switches 189081 (2355.78)
Sleeps 99231.5 (800.358)
Link: http://lkml.kernel.org/r/1464295031-26375-3-git-send-email-thgarnie@xxxxxxxxxx
Signed-off-by: Thomas Garnier <thgarnie@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/slub_def.h | 5 +
init/Kconfig | 4 -
mm/slub.c | 133 +++++++++++++++++++++++++++++++++++--
3 files changed, 133 insertions(+), 9 deletions(-)
diff -puN include/linux/slub_def.h~mm-slub-freelist-randomization include/linux/slub_def.h
--- a/include/linux/slub_def.h~mm-slub-freelist-randomization
+++ a/include/linux/slub_def.h
@@ -99,6 +99,11 @@ struct kmem_cache {
*/
int remote_node_defrag_ratio;
#endif
+
+#ifdef CONFIG_SLAB_FREELIST_RANDOM
+ unsigned int *random_seq;
+#endif
+
struct kmem_cache_node *node[MAX_NUMNODES];
};
diff -puN init/Kconfig~mm-slub-freelist-randomization init/Kconfig
--- a/init/Kconfig~mm-slub-freelist-randomization
+++ a/init/Kconfig
@@ -1784,10 +1784,10 @@ endchoice
config SLAB_FREELIST_RANDOM
default n
- depends on SLAB
+ depends on SLAB || SLUB
bool "SLAB freelist randomization"
help
- Randomizes the freelist order used on creating new SLABs. This
+ Randomizes the freelist order used on creating new pages. This
security feature reduces the predictability of the kernel slab
allocator against heap overflows.
diff -puN mm/slub.c~mm-slub-freelist-randomization mm/slub.c
--- a/mm/slub.c~mm-slub-freelist-randomization
+++ a/mm/slub.c
@@ -1405,6 +1405,109 @@ static inline struct page *alloc_slab_pa
return page;
}
+#ifdef CONFIG_SLAB_FREELIST_RANDOM
+/* Pre-initialize the random sequence cache */
+static int init_cache_random_seq(struct kmem_cache *s)
+{
+ int err;
+ unsigned long i, count = oo_objects(s->oo);
+
+ err = cache_random_seq_create(s, count, GFP_KERNEL);
+ if (err) {
+ pr_err("SLUB: Unable to initialize free list for %s\n",
+ s->name);
+ return err;
+ }
+
+ /* Transform to an offset on the set of pages */
+ if (s->random_seq) {
+ for (i = 0; i < count; i++)
+ s->random_seq[i] *= s->size;
+ }
+ return 0;
+}
+
+/* Initialize each random sequence freelist per cache */
+static void __init init_freelist_randomization(void)
+{
+ struct kmem_cache *s;
+
+ mutex_lock(&slab_mutex);
+
+ list_for_each_entry(s, &slab_caches, list)
+ init_cache_random_seq(s);
+
+ mutex_unlock(&slab_mutex);
+}
+
+/* Get the next entry on the pre-computed freelist randomized */
+static void *next_freelist_entry(struct kmem_cache *s, struct page *page,
+ unsigned long *pos, void *start,
+ unsigned long page_limit,
+ unsigned long freelist_count)
+{
+ unsigned int idx;
+
+ /*
+ * If the target page allocation failed, the number of objects on the
+ * page might be smaller than the usual size defined by the cache.
+ */
+ do {
+ idx = s->random_seq[*pos];
+ *pos += 1;
+ if (*pos >= freelist_count)
+ *pos = 0;
+ } while (unlikely(idx >= page_limit));
+
+ return (char *)start + idx;
+}
+
+/* Shuffle the single linked freelist based on a random pre-computed sequence */
+static bool shuffle_freelist(struct kmem_cache *s, struct page *page)
+{
+ void *start;
+ void *cur;
+ void *next;
+ unsigned long idx, pos, page_limit, freelist_count;
+
+ if (page->objects < 2 || !s->random_seq)
+ return false;
+
+ freelist_count = oo_objects(s->oo);
+ pos = get_random_int() % freelist_count;
+
+ page_limit = page->objects * s->size;
+ start = fixup_red_left(s, page_address(page));
+
+ /* First entry is used as the base of the freelist */
+ cur = next_freelist_entry(s, page, &pos, start, page_limit,
+ freelist_count);
+ page->freelist = cur;
+
+ for (idx = 1; idx < page->objects; idx++) {
+ setup_object(s, page, cur);
+ next = next_freelist_entry(s, page, &pos, start, page_limit,
+ freelist_count);
+ set_freepointer(s, cur, next);
+ cur = next;
+ }
+ setup_object(s, page, cur);
+ set_freepointer(s, cur, NULL);
+
+ return true;
+}
+#else
+static inline int init_cache_random_seq(struct kmem_cache *s)
+{
+ return 0;
+}
+static inline void init_freelist_randomization(void) { }
+static inline bool shuffle_freelist(struct kmem_cache *s, struct page *page)
+{
+ return false;
+}
+#endif /* CONFIG_SLAB_FREELIST_RANDOM */
+
static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
{
struct page *page;
@@ -1412,6 +1515,7 @@ static struct page *allocate_slab(struct
gfp_t alloc_gfp;
void *start, *p;
int idx, order;
+ bool shuffle;
flags &= gfp_allowed_mask;
@@ -1473,15 +1577,19 @@ static struct page *allocate_slab(struct
kasan_poison_slab(page);
- for_each_object_idx(p, idx, s, start, page->objects) {
- setup_object(s, page, p);
- if (likely(idx < page->objects))
- set_freepointer(s, p, p + s->size);
- else
- set_freepointer(s, p, NULL);
+ shuffle = shuffle_freelist(s, page);
+
+ if (!shuffle) {
+ for_each_object_idx(p, idx, s, start, page->objects) {
+ setup_object(s, page, p);
+ if (likely(idx < page->objects))
+ set_freepointer(s, p, p + s->size);
+ else
+ set_freepointer(s, p, NULL);
+ }
+ page->freelist = fixup_red_left(s, start);
}
- page->freelist = fixup_red_left(s, start);
page->inuse = page->objects;
page->frozen = 1;
@@ -3207,6 +3315,7 @@ static void free_kmem_cache_nodes(struct
void __kmem_cache_release(struct kmem_cache *s)
{
+ cache_random_seq_destroy(s);
free_percpu(s->cpu_slab);
free_kmem_cache_nodes(s);
}
@@ -3431,6 +3540,13 @@ static int kmem_cache_open(struct kmem_c
#ifdef CONFIG_NUMA
s->remote_node_defrag_ratio = 1000;
#endif
+
+ /* Initialize the pre-computed randomized freelist if slab is up */
+ if (slab_state >= UP) {
+ if (init_cache_random_seq(s))
+ goto error;
+ }
+
if (!init_kmem_cache_nodes(s))
goto error;
@@ -3947,6 +4063,9 @@ void __init kmem_cache_init(void)
setup_kmalloc_cache_index_table();
create_kmalloc_caches(0);
+ /* Setup random freelists for each cache */
+ init_freelist_randomization();
+
#ifdef CONFIG_SMP
register_cpu_notifier(&slab_notifier);
#endif
_
Patches currently in -mm which might be from thgarnie@xxxxxxxxxx are
mm-reorganize-slab-freelist-randomization.patch
mm-slub-freelist-randomization.patch
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