[PATCH v2 1/3] bpf: allow zero-initializing hash map seed
From: Lorenz Bauer <hidden>
Date: 2018-10-08 17:44:25
Also in:
netdev
Subsystem:
bpf [general] (safe dynamic programs and tools), the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, Linus Torvalds
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 <redacted> --- 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) /* 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