Commit 03e69b50 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller

ebpf: add prandom helper for packet sampling

This work is similar to commit 4cd3675e ("filter: added BPF
random opcode") and adds a possibility for packet sampling in eBPF.

Currently, this is only possible in classic BPF and useful to
combine sampling with f.e. packet sockets, possible also with tc.

Example function proto-type looks like:

  u32 (*prandom_u32)(void) = (void *)BPF_FUNC_get_prandom_u32;
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 12028820
......@@ -154,4 +154,6 @@ extern const struct bpf_func_proto bpf_map_lookup_elem_proto;
extern const struct bpf_func_proto bpf_map_update_elem_proto;
extern const struct bpf_func_proto bpf_map_delete_elem_proto;
extern const struct bpf_func_proto bpf_get_prandom_u32_proto;
#endif /* _LINUX_BPF_H */
......@@ -165,6 +165,7 @@ enum bpf_func_id {
BPF_FUNC_map_lookup_elem, /* void *map_lookup_elem(&map, &key) */
BPF_FUNC_map_update_elem, /* int map_update_elem(&map, &key, &value, flags) */
BPF_FUNC_map_delete_elem, /* int map_delete_elem(&map, &key) */
BPF_FUNC_get_prandom_u32, /* u32 prandom_u32(void) */
__BPF_FUNC_MAX_ID,
};
......
......@@ -661,6 +661,8 @@ const struct bpf_func_proto bpf_map_lookup_elem_proto __weak;
const struct bpf_func_proto bpf_map_update_elem_proto __weak;
const struct bpf_func_proto bpf_map_delete_elem_proto __weak;
const struct bpf_func_proto bpf_get_prandom_u32_proto __weak;
/* To execute LD_ABS/LD_IND instructions __bpf_prog_run() may call
* skb_copy_bits(), so provide a weak definition of it for NET-less config.
*/
......
......@@ -11,6 +11,7 @@
*/
#include <linux/bpf.h>
#include <linux/rcupdate.h>
#include <linux/random.h>
/* If kernel subsystem is allowing eBPF programs to call this function,
* inside its own verifier_ops->get_func_proto() callback it should return
......@@ -87,3 +88,14 @@ const struct bpf_func_proto bpf_map_delete_elem_proto = {
.arg1_type = ARG_CONST_MAP_PTR,
.arg2_type = ARG_PTR_TO_MAP_KEY,
};
static u64 bpf_get_prandom_u32(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
{
return prandom_u32();
}
const struct bpf_func_proto bpf_get_prandom_u32_proto = {
.func = bpf_get_prandom_u32,
.gpl_only = false,
.ret_type = RET_INTEGER,
};
......@@ -1139,6 +1139,8 @@ sk_filter_func_proto(enum bpf_func_id func_id)
return &bpf_map_update_elem_proto;
case BPF_FUNC_map_delete_elem:
return &bpf_map_delete_elem_proto;
case BPF_FUNC_get_prandom_u32:
return &bpf_get_prandom_u32_proto;
default:
return NULL;
}
......
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