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Merge branch 'bpf-zero-hash-seed'

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Lorenz Bauer says:

====================
Allow forcing the seed of a hash table to zero, for deterministic
execution during benchmarking and testing.

Changes from v2:
* Change ordering of BPF_F_ZERO_SEED in linux/bpf.h

Comments adressed from v1:
* Add comment to discourage production use to linux/bpf.h
* Require CAP_SYS_ADMIN
====================

Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Daniel Borkmann 2018-11-20 00:53:40 +01:00
commit bbe5d311be
4 changed files with 84 additions and 19 deletions
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9
include/uapi/linux/bpf.h
View File

@ -257,9 +257,6 @@ enum bpf_attach_type {
/* Specify numa node during map creation */
#define BPF_F_NUMA_NODE (1U << 2)
/* flags for BPF_PROG_QUERY */
#define BPF_F_QUERY_EFFECTIVE (1U << 0)
#define BPF_OBJ_NAME_LEN 16U
/* Flags for accessing BPF object */
@ -269,6 +266,12 @@ enum bpf_attach_type {
/* Flag for stack_map, store build_id+offset instead of pointer */
#define BPF_F_STACK_BUILD_ID (1U << 5)
/* Zero-initialize hash function seed. This should only be used for testing. */
#define BPF_F_ZERO_SEED (1U << 6)
/* flags for BPF_PROG_QUERY */
#define BPF_F_QUERY_EFFECTIVE (1U << 0)
enum bpf_stack_build_id_status {
/* user space need an empty entry to identify end of a trace */
BPF_STACK_BUILD_ID_EMPTY = 0,

13
kernel/bpf/hashtab.c
View File

@ -23,7 +23,7 @@
#define HTAB_CREATE_FLAG_MASK \
(BPF_F_NO_PREALLOC | BPF_F_NO_COMMON_LRU | BPF_F_NUMA_NODE | \
BPF_F_RDONLY | BPF_F_WRONLY)
BPF_F_RDONLY | BPF_F_WRONLY | BPF_F_ZERO_SEED)
struct bucket {
struct hlist_nulls_head head;
@ -244,6 +244,7 @@ static int htab_map_alloc_check(union bpf_attr *attr)
*/
bool percpu_lru = (attr->map_flags & BPF_F_NO_COMMON_LRU);
bool prealloc = !(attr->map_flags & BPF_F_NO_PREALLOC);
bool zero_seed = (attr->map_flags & BPF_F_ZERO_SEED);
int numa_node = bpf_map_attr_numa_node(attr);
BUILD_BUG_ON(offsetof(struct htab_elem, htab) !=
@ -257,6 +258,10 @@ static int htab_map_alloc_check(union bpf_attr *attr)
*/
return -EPERM;
if (zero_seed && !capable(CAP_SYS_ADMIN))
/* Guard against local DoS, and discourage production use. */
return -EPERM;
if (attr->map_flags & ~HTAB_CREATE_FLAG_MASK)
/* reserved bits should not be used */
return -EINVAL;
@ -373,7 +378,11 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
if (!htab->buckets)
goto free_htab;
htab->hashrnd = get_random_int();
if (htab->map.map_flags & BPF_F_ZERO_SEED)
htab->hashrnd = 0;
else
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);

13
tools/include/uapi/linux/bpf.h
View File

@ -257,9 +257,6 @@ enum bpf_attach_type {
/* Specify numa node during map creation */
#define BPF_F_NUMA_NODE (1U << 2)
/* flags for BPF_PROG_QUERY */
#define BPF_F_QUERY_EFFECTIVE (1U << 0)
#define BPF_OBJ_NAME_LEN 16U
/* Flags for accessing BPF object */
@ -269,6 +266,12 @@ enum bpf_attach_type {
/* Flag for stack_map, store build_id+offset instead of pointer */
#define BPF_F_STACK_BUILD_ID (1U << 5)
/* Zero-initialize hash function seed. This should only be used for testing. */
#define BPF_F_ZERO_SEED (1U << 6)
/* flags for BPF_PROG_QUERY */
#define BPF_F_QUERY_EFFECTIVE (1U << 0)
enum bpf_stack_build_id_status {
/* user space need an empty entry to identify end of a trace */
BPF_STACK_BUILD_ID_EMPTY = 0,
@ -2201,6 +2204,8 @@ union bpf_attr {
* **CONFIG_NET** configuration option.
* Return
* Pointer to *struct bpf_sock*, or NULL in case of failure.
* For sockets with reuseport option, *struct bpf_sock*
* return is from reuse->socks[] using hash of the packet.
*
* struct bpf_sock *bpf_sk_lookup_udp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u32 netns, u64 flags)
* Description
@ -2233,6 +2238,8 @@ union bpf_attr {
* **CONFIG_NET** configuration option.
* Return
* Pointer to *struct bpf_sock*, or NULL in case of failure.
* For sockets with reuseport option, *struct bpf_sock*
* return is from reuse->socks[] using hash of the packet.
*
* int bpf_sk_release(struct bpf_sock *sk)
* Description

68
tools/testing/selftests/bpf/test_maps.c
View File

@ -258,23 +258,35 @@ static void test_hashmap_percpu(int task, void *data)
close(fd);
}
static int helper_fill_hashmap(int max_entries)
{
int i, fd, ret;
long long key, value;
fd = bpf_create_map(BPF_MAP_TYPE_HASH, sizeof(key), sizeof(value),
max_entries, map_flags);
CHECK(fd < 0,
"failed to create hashmap",
"err: %s, flags: 0x%x\n", strerror(errno), map_flags);
for (i = 0; i < max_entries; i++) {
key = i; value = key;
ret = bpf_map_update_elem(fd, &key, &value, BPF_NOEXIST);
CHECK(ret != 0,
"can't update hashmap",
"err: %s\n", strerror(ret));
}
return fd;
}
static void test_hashmap_walk(int task, void *data)
{
int fd, i, max_entries = 1000;
long long key, value, next_key;
bool next_key_valid = true;
fd = bpf_create_map(BPF_MAP_TYPE_HASH, sizeof(key), sizeof(value),
max_entries, map_flags);
if (fd < 0) {
printf("Failed to create hashmap '%s'!\n", strerror(errno));
exit(1);
}
for (i = 0; i < max_entries; i++) {
key = i; value = key;
assert(bpf_map_update_elem(fd, &key, &value, BPF_NOEXIST) == 0);
}
fd = helper_fill_hashmap(max_entries);
for (i = 0; bpf_map_get_next_key(fd, !i ? NULL : &key,
&next_key) == 0; i++) {
@ -306,6 +318,39 @@ static void test_hashmap_walk(int task, void *data)
close(fd);
}
static void test_hashmap_zero_seed(void)
{
int i, first, second, old_flags;
long long key, next_first, next_second;
old_flags = map_flags;
map_flags |= BPF_F_ZERO_SEED;
first = helper_fill_hashmap(3);
second = helper_fill_hashmap(3);
for (i = 0; ; i++) {
void *key_ptr = !i ? NULL : &key;
if (bpf_map_get_next_key(first, key_ptr, &next_first) != 0)
break;
CHECK(bpf_map_get_next_key(second, key_ptr, &next_second) != 0,
"next_key for second map must succeed",
"key_ptr: %p", key_ptr);
CHECK(next_first != next_second,
"keys must match",
"i: %d first: %lld second: %lld\n", i,
next_first, next_second);
key = next_first;
}
map_flags = old_flags;
close(first);
close(second);
}
static void test_arraymap(int task, void *data)
{
int key, next_key, fd;
@ -1534,6 +1579,7 @@ static void run_all_tests(void)
test_hashmap(0, NULL);
test_hashmap_percpu(0, NULL);
test_hashmap_walk(0, NULL);
test_hashmap_zero_seed();
test_arraymap(0, NULL);
test_arraymap_percpu(0, NULL);