diff options
| author | Lorenz Bauer <lmb@cloudflare.com> | 2018-11-16 11:41:08 +0000 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2018-11-20 00:53:39 +0100 |
| commit | 96b3b6c9091d23289721350e32c63cc8749686be (patch) | |
| tree | 94552c4164204873c93534fb2383044e122d0488 | |
| parent | 23499442c319412aa8e54e7a939e2eb531bdd77d (diff) | |
| download | linux-96b3b6c9091d23289721350e32c63cc8749686be.tar.gz linux-96b3b6c9091d23289721350e32c63cc8749686be.tar.bz2 linux-96b3b6c9091d23289721350e32c63cc8749686be.zip | |
bpf: allow zero-initializing hash map seed
Add a new flag BPF_F_ZERO_SEED, which forces a hash map
to initialize the seed to zero. This is useful when doing
performance analysis both on individual BPF programs, as
well as the kernel's hash table implementation.
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
| -rw-r--r-- | include/uapi/linux/bpf.h | 3 | ||||
| -rw-r--r-- | kernel/bpf/hashtab.c | 13 |
2 files changed, 14 insertions, 2 deletions
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 47d606d744cc..8c01b89a4cb4 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -269,6 +269,9 @@ 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) + enum bpf_stack_build_id_status { /* user space need an empty entry to identify end of a trace */ BPF_STACK_BUILD_ID_EMPTY = 0, diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index 2c1790288138..4b7c76765d9d 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -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); |