Commit c0203475 authored by Daniel Borkmann's avatar Daniel Borkmann
Browse files

bpf: use per htab salt for bucket hash 



All BPF hash and LRU maps currently have a known and global seed
we feed into jhash() which is 0. This is suboptimal, thus fix it
by generating a random seed upon hashtab setup time which we can
later on feed into jhash() on lookup, update and deletions.

Fixes: 0f8e4bd8 ("bpf: add hashtable type of eBPF maps")
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Reviewed-by: default avatarEduardo Valentin <eduval@amazon.com>
parent 9b2e0388

kernel/bpf/hashtab.c

+13 −10
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 
#include <linux/jhash.h>

#include <linux/filter.h>

#include <linux/rculist_nulls.h>

#include <linux/random.h>

#include <uapi/linux/btf.h>

#include "percpu_freelist.h"

#include "bpf_lru_list.h"
@@ -41,6 +42,7 @@ struct bpf_htab { 
	atomic_t count;	/* number of elements in this hashtable */

	u32 n_buckets;	/* number of hash buckets */

	u32 elem_size;	/* size of each element in bytes */

	u32 hashrnd;

};



/* each htab element is struct htab_elem + key + value */
@@ -371,6 +373,7 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 
	if (!htab->buckets)

		goto free_htab;



	htab->hashrnd = get_random_int();

	for (i = 0; i < htab->n_buckets; i++) {

		INIT_HLIST_NULLS_HEAD(&htab->buckets[i].head, i);

		raw_spin_lock_init(&htab->buckets[i].lock);
@@ -402,9 +405,9 @@ free_htab: 
	return ERR_PTR(err);

}



static inline u32 htab_map_hash(const void *key, u32 key_len)

static inline u32 htab_map_hash(const void *key, u32 key_len, u32 hashrnd)

{

	return jhash(key, key_len, 0);

	return jhash(key, key_len, hashrnd);

}



static inline struct bucket *__select_bucket(struct bpf_htab *htab, u32 hash)
@@ -470,7 +473,7 @@ static void *__htab_map_lookup_elem(struct bpf_map *map, void *key) 


	key_size = map->key_size;



	hash = htab_map_hash(key, key_size);

	hash = htab_map_hash(key, key_size, htab->hashrnd);



	head = select_bucket(htab, hash);
@@ -597,7 +600,7 @@ static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key) 
	if (!key)

		goto find_first_elem;



	hash = htab_map_hash(key, key_size);

	hash = htab_map_hash(key, key_size, htab->hashrnd);



	head = select_bucket(htab, hash);
@@ -824,7 +827,7 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value, 


	key_size = map->key_size;



	hash = htab_map_hash(key, key_size);

	hash = htab_map_hash(key, key_size, htab->hashrnd);



	b = __select_bucket(htab, hash);

	head = &b->head;
@@ -880,7 +883,7 @@ static int htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value, 


	key_size = map->key_size;



	hash = htab_map_hash(key, key_size);

	hash = htab_map_hash(key, key_size, htab->hashrnd);



	b = __select_bucket(htab, hash);

	head = &b->head;
@@ -945,7 +948,7 @@ static int __htab_percpu_map_update_elem(struct bpf_map *map, void *key, 


	key_size = map->key_size;



	hash = htab_map_hash(key, key_size);

	hash = htab_map_hash(key, key_size, htab->hashrnd);



	b = __select_bucket(htab, hash);

	head = &b->head;
@@ -998,7 +1001,7 @@ static int __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key, 


	key_size = map->key_size;



	hash = htab_map_hash(key, key_size);

	hash = htab_map_hash(key, key_size, htab->hashrnd);



	b = __select_bucket(htab, hash);

	head = &b->head;
@@ -1071,7 +1074,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key) 


	key_size = map->key_size;



	hash = htab_map_hash(key, key_size);

	hash = htab_map_hash(key, key_size, htab->hashrnd);

	b = __select_bucket(htab, hash);

	head = &b->head;
@@ -1103,7 +1106,7 @@ static int htab_lru_map_delete_elem(struct bpf_map *map, void *key) 


	key_size = map->key_size;



	hash = htab_map_hash(key, key_size);

	hash = htab_map_hash(key, key_size, htab->hashrnd);

	b = __select_bucket(htab, hash);

	head = &b->head;

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