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

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

include/linux/bpf.h

+2 −0
Original line number Diff line number Diff line
@@ -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 */

include/uapi/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -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,

};

kernel/bpf/core.c

+2 −0
Original line number Diff line number Diff line
@@ -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.

 */

kernel/bpf/helpers.c

+12 −0
Original line number Diff line number Diff line
@@ -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,

};

net/core/filter.c

+2 −0
Original line number Diff line number Diff line
@@ -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;

	}