On Mon, Oct 8, 2018 at 3:34 AM Lorenz Bauer <lmb@xxxxxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxxxxxx>
> ---
> include/uapi/linux/bpf.h | 2 ++
> kernel/bpf/hashtab.c | 13 +++++++++++--
> 2 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index f9187b41dff6..2c121f862082 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -253,6 +253,8 @@ enum bpf_attach_type {
> #define BPF_F_NO_COMMON_LRU (1U << 1)
> /* Specify numa node during map creation */
> #define BPF_F_NUMA_NODE (1U << 2)
> +/* Zero-initialize hash function seed. This should only be used for testing. */
> +#define BPF_F_ZERO_SEED (1U << 6)
Please add this line after
#define BPF_F_STACK_BUILD_ID (1U << 5)
Other than this
Acked-by: Song Liu <songliubraving@xxxxxx>
>
> /* flags for BPF_PROG_QUERY */
> #define BPF_F_QUERY_EFFECTIVE (1U << 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);
> --
> 2.17.1
>
