1// SPDX-License-Identifier: GPL-2.0
 2// Copyright (c) 2018 Facebook
 3
 4#include <linux/bpf.h>
 5#include <bpf/bpf_helpers.h>
 6
 7#ifndef PERF_MAX_STACK_DEPTH
 8#define PERF_MAX_STACK_DEPTH         127
 9#endif
10
11struct {
12	__uint(type, BPF_MAP_TYPE_ARRAY);
13	__uint(max_entries, 1);
14	__type(key, __u32);
15	__type(value, __u32);
16} control_map SEC(".maps");
17
18struct {
19	__uint(type, BPF_MAP_TYPE_HASH);
20	__uint(max_entries, 16384);
21	__type(key, __u32);
22	__type(value, __u32);
23} stackid_hmap SEC(".maps");
24
25typedef struct bpf_stack_build_id stack_trace_t[PERF_MAX_STACK_DEPTH];
26
27struct {
28	__uint(type, BPF_MAP_TYPE_STACK_TRACE);
29	__uint(max_entries, 128);
30	__uint(map_flags, BPF_F_STACK_BUILD_ID);
31	__uint(key_size, sizeof(__u32));
32	__uint(value_size, sizeof(stack_trace_t));
33} stackmap SEC(".maps");
34
35struct {
36	__uint(type, BPF_MAP_TYPE_ARRAY);
37	__uint(max_entries, 128);
38	__type(key, __u32);
39	__type(value, stack_trace_t);
40} stack_amap SEC(".maps");
41
42/* taken from /sys/kernel/debug/tracing/events/random/urandom_read/format */
43struct random_urandom_args {
44	unsigned long long pad;
45	int got_bits;
46	int pool_left;
47	int input_left;
48};
49
50SEC("tracepoint/random/urandom_read")
51int oncpu(struct random_urandom_args *args)
52{
53	__u32 max_len = sizeof(struct bpf_stack_build_id)
54			* PERF_MAX_STACK_DEPTH;
55	__u32 key = 0, val = 0, *value_p;
56	void *stack_p;
57
58	value_p = bpf_map_lookup_elem(&control_map, &key);
59	if (value_p && *value_p)
60		return 0; /* skip if non-zero *value_p */
61
62	/* The size of stackmap and stackid_hmap should be the same */
63	key = bpf_get_stackid(args, &stackmap, BPF_F_USER_STACK);
64	if ((int)key >= 0) {
65		bpf_map_update_elem(&stackid_hmap, &key, &val, 0);
66		stack_p = bpf_map_lookup_elem(&stack_amap, &key);
67		if (stack_p)
68			bpf_get_stack(args, stack_p, max_len,
69				      BPF_F_USER_STACK | BPF_F_USER_BUILD_ID);
70	}
71
72	return 0;
73}
74
75char _license[] SEC("license") = "GPL";
76__u32 _version SEC("version") = 1; /* ignored by tracepoints, required by libbpf.a */