This commit reorganizes the previous SLAB freelist randomization to
prepare for the SLUB implementation. It moves functions that will be
shared to slab_common.
The entropy functions are changed to align with the SLUB implementation,
now using get_random_(int|long) functions. These functions were chosen
because they provide a bit more entropy early on boot and better
performance when specific arch instructions are not available.
Signed-off-by: Thomas Garnier <thgarnie@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
Based on next-20160526
---
include/linux/slab_def.h | 2 +-
mm/slab.c | 80 ++++++++++++------------------------------------
mm/slab.h | 14 +++++++++
mm/slab_common.c | 47 ++++++++++++++++++++++++++++
4 files changed, 82 insertions(+), 61 deletions(-)
diff --git a/include/linux/slab_def.h b/include/linux/slab_def.h
index 8694f7a..339ba02 100644
--- a/include/linux/slab_def.h
+++ b/include/linux/slab_def.h
@@ -81,7 +81,7 @@ struct kmem_cache {
#endif
#ifdef CONFIG_SLAB_FREELIST_RANDOM
- void *random_seq;
+ unsigned int *random_seq;
#endif
struct kmem_cache_node *node[MAX_NUMNODES];
diff --git a/mm/slab.c b/mm/slab.c
index cc8bbc1..763096a 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1236,61 +1236,6 @@ static void __init set_up_node(struct kmem_cache *cachep, int index)
}
}
-#ifdef CONFIG_SLAB_FREELIST_RANDOM
-static void freelist_randomize(struct rnd_state *state, freelist_idx_t *list,
- size_t count)
-{
- size_t i;
- unsigned int rand;
-
- for (i = 0; i < count; i++)
- list[i] = i;
-
- /* Fisher-Yates shuffle */
- for (i = count - 1; i > 0; i--) {
- rand = prandom_u32_state(state);
- rand %= (i + 1);
- swap(list[i], list[rand]);
- }
-}
-
-/* Create a random sequence per cache */
-static int cache_random_seq_create(struct kmem_cache *cachep, gfp_t gfp)
-{
- unsigned int seed, count = cachep->num;
- struct rnd_state state;
-
- if (count < 2)
- return 0;
-
- /* If it fails, we will just use the global lists */
- cachep->random_seq = kcalloc(count, sizeof(freelist_idx_t), gfp);
- if (!cachep->random_seq)
- return -ENOMEM;
-
- /* Get best entropy at this stage */
- get_random_bytes_arch(&seed, sizeof(seed));
- prandom_seed_state(&state, seed);
-
- freelist_randomize(&state, cachep->random_seq, count);
- return 0;
-}
-
-/* Destroy the per-cache random freelist sequence */
-static void cache_random_seq_destroy(struct kmem_cache *cachep)
-{
- kfree(cachep->random_seq);
- cachep->random_seq = NULL;
-}
-#else
-static inline int cache_random_seq_create(struct kmem_cache *cachep, gfp_t gfp)
-{
- return 0;
-}
-static inline void cache_random_seq_destroy(struct kmem_cache *cachep) { }
-#endif /* CONFIG_SLAB_FREELIST_RANDOM */
-
-
/*
* Initialisation. Called after the page allocator have been initialised and
* before smp_init().
@@ -2535,7 +2480,7 @@ static void cache_init_objs_debug(struct kmem_cache *cachep, struct page *page)
union freelist_init_state {
struct {
unsigned int pos;
- freelist_idx_t *list;
+ unsigned int *list;
unsigned int count;
unsigned int rand;
};
@@ -2554,7 +2499,7 @@ static bool freelist_state_initialize(union freelist_init_state *state,
unsigned int rand;
/* Use best entropy available to define a random shift */
- get_random_bytes_arch(&rand, sizeof(rand));
+ rand = get_random_int();
/* Use a random state if the pre-computed list is not available */
if (!cachep->random_seq) {
@@ -2576,13 +2521,20 @@ static freelist_idx_t next_random_slot(union freelist_init_state *state)
return (state->list[state->pos++] + state->rand) % state->count;
}
+/* Swap two freelist entries */
+static void swap_free_obj(struct page *page, unsigned int a, unsigned int b)
+{
+ swap(((freelist_idx_t *)page->freelist)[a],
+ ((freelist_idx_t *)page->freelist)[b]);
+}
+
/*
* Shuffle the freelist initialization state based on pre-computed lists.
* return true if the list was successfully shuffled, false otherwise.
*/
static bool shuffle_freelist(struct kmem_cache *cachep, struct page *page)
{
- unsigned int objfreelist = 0, i, count = cachep->num;
+ unsigned int objfreelist = 0, i, rand, count = cachep->num;
union freelist_init_state state;
bool precomputed;
@@ -2607,7 +2559,15 @@ static bool shuffle_freelist(struct kmem_cache *cachep, struct page *page)
* Later use a pre-computed list for speed.
*/
if (!precomputed) {
- freelist_randomize(&state.rnd_state, page->freelist, count);
+ for (i = 0; i < count; i++)
+ set_free_obj(page, i, i);
+
+ /* Fisher-Yates shuffle */
+ for (i = count - 1; i > 0; i--) {
+ rand = prandom_u32_state(&state.rnd_state);
+ rand %= (i + 1);
+ swap_free_obj(page, i, rand);
+ }
} else {
for (i = 0; i < count; i++)
set_free_obj(page, i, next_random_slot(&state));
@@ -3979,7 +3939,7 @@ static int enable_cpucache(struct kmem_cache *cachep, gfp_t gfp)
int shared = 0;
int batchcount = 0;
- err = cache_random_seq_create(cachep, gfp);
+ err = cache_random_seq_create(cachep, cachep->num, gfp);
if (err)
goto end;
diff --git a/mm/slab.h b/mm/slab.h
index dedb1a9..5fa8b8f 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -42,6 +42,7 @@ struct kmem_cache {
#include <linux/kmemcheck.h>
#include <linux/kasan.h>
#include <linux/kmemleak.h>
+#include <linux/random.h>
/*
* State of the slab allocator.
@@ -464,4 +465,17 @@ int memcg_slab_show(struct seq_file *m, void *p);
void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr);
+#ifdef CONFIG_SLAB_FREELIST_RANDOM
+int cache_random_seq_create(struct kmem_cache *cachep, unsigned int count,
+ gfp_t gfp);
+void cache_random_seq_destroy(struct kmem_cache *cachep);
+#else
+static inline int cache_random_seq_create(struct kmem_cache *cachep,
+ unsigned int count, gfp_t gfp)
+{
+ return 0;
+}
+static inline void cache_random_seq_destroy(struct kmem_cache *cachep) { }
+#endif /* CONFIG_SLAB_FREELIST_RANDOM */
+
#endif /* MM_SLAB_H */
diff --git a/mm/slab_common.c b/mm/slab_common.c
index a65dad7..eb1789b 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1142,6 +1142,53 @@ int memcg_slab_show(struct seq_file *m, void *p)
}
#endif
+#ifdef CONFIG_SLAB_FREELIST_RANDOM
+/* Randomize a generic freelist */
+static void freelist_randomize(struct rnd_state *state, unsigned int *list,
+ size_t count)
+{
+ size_t i;
+ unsigned int rand;
+
+ for (i = 0; i < count; i++)
+ list[i] = i;
+
+ /* Fisher-Yates shuffle */
+ for (i = count - 1; i > 0; i--) {
+ rand = prandom_u32_state(state);
+ rand %= (i + 1);
+ swap(list[i], list[rand]);
+ }
+}
+
+/* Create a random sequence per cache */
+int cache_random_seq_create(struct kmem_cache *cachep, unsigned int count,
+ gfp_t gfp)
+{
+ struct rnd_state state;
+
+ if (count < 2 || cachep->random_seq)
+ return 0;
+
+ cachep->random_seq = kcalloc(count, sizeof(unsigned int), gfp);
+ if (!cachep->random_seq)
+ return -ENOMEM;
+
+ /* Get best entropy at this stage of boot */
+ prandom_seed_state(&state, get_random_long());
+
+ freelist_randomize(&state, cachep->random_seq, count);
+ return 0;
+}
+
+/* Destroy the per-cache random freelist sequence */
+void cache_random_seq_destroy(struct kmem_cache *cachep)
+{
+ kfree(cachep->random_seq);
+ cachep->random_seq = NULL;
+}
+#endif /* CONFIG_SLAB_FREELIST_RANDOM */
+
/*
* slabinfo_op - iterator that generates /proc/slabinfo
*
--
2.8.0.rc3.226.g39d4020
--
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