1// SPDX-License-Identifier: GPL-2.0
 2// Copyright (c) 2018 Facebook
 3
 4#include <linux/bpf.h>
 5#include "bpf_helpers.h"
 6
 7#ifndef PERF_MAX_STACK_DEPTH
 8#define PERF_MAX_STACK_DEPTH         127
 9#endif
10
11struct bpf_map_def SEC("maps") control_map = {
12	.type = BPF_MAP_TYPE_ARRAY,
13	.key_size = sizeof(__u32),
14	.value_size = sizeof(__u32),
15	.max_entries = 1,
16};
17
18struct bpf_map_def SEC("maps") stackid_hmap = {
19	.type = BPF_MAP_TYPE_HASH,
20	.key_size = sizeof(__u32),
21	.value_size = sizeof(__u32),
22	.max_entries = 10000,
23};
24
25struct bpf_map_def SEC("maps") stackmap = {
26	.type = BPF_MAP_TYPE_STACK_TRACE,
27	.key_size = sizeof(__u32),
28	.value_size = sizeof(struct bpf_stack_build_id)
29		* PERF_MAX_STACK_DEPTH,
30	.max_entries = 128,
31	.map_flags = BPF_F_STACK_BUILD_ID,
32};
33
34/* taken from /sys/kernel/debug/tracing/events/random/urandom_read/format */
35struct random_urandom_args {
36	unsigned long long pad;
37	int got_bits;
38	int pool_left;
39	int input_left;
40};
41
42SEC("tracepoint/random/urandom_read")
43int oncpu(struct random_urandom_args *args)
44{
45	__u32 key = 0, val = 0, *value_p;
46
47	value_p = bpf_map_lookup_elem(&control_map, &key);
48	if (value_p && *value_p)
49		return 0; /* skip if non-zero *value_p */
50
51	/* The size of stackmap and stackid_hmap should be the same */
52	key = bpf_get_stackid(args, &stackmap, BPF_F_USER_STACK);
53	if ((int)key >= 0)
54		bpf_map_update_elem(&stackid_hmap, &key, &val, 0);
55
56	return 0;
57}
58
59char _license[] SEC("license") = "GPL";
60__u32 _version SEC("version") = 1; /* ignored by tracepoints, required by libbpf.a */