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 
11 struct {
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 
18 struct {
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 
25 typedef struct bpf_stack_build_id stack_trace_t[PERF_MAX_STACK_DEPTH];
26 
27 struct {
28 	__uint(type, BPF_MAP_TYPE_STACK_TRACE);
29 	__uint(max_entries, 128);
30 	__uint(map_flags, BPF_F_STACK_BUILD_ID);
31 	__type(key, __u32);
32 	__type(value, stack_trace_t);
33 } stackmap SEC(".maps");
34 
35 struct {
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 */
43 struct random_urandom_args {
44 	unsigned long long pad;
45 	int got_bits;
46 	int pool_left;
47 	int input_left;
48 };
49 
50 SEC("tracepoint/random/urandom_read")
51 int 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 
75 char _license[] SEC("license") = "GPL";
76