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 SEC("kprobe/urandom_read_iter")
oncpu(struct pt_regs * args)43 int oncpu(struct pt_regs *args)
44 {
45 __u32 max_len = sizeof(struct bpf_stack_build_id)
46 * PERF_MAX_STACK_DEPTH;
47 __u32 key = 0, val = 0, *value_p;
48 void *stack_p;
49
50 value_p = bpf_map_lookup_elem(&control_map, &key);
51 if (value_p && *value_p)
52 return 0; /* skip if non-zero *value_p */
53
54 /* The size of stackmap and stackid_hmap should be the same */
55 key = bpf_get_stackid(args, &stackmap, BPF_F_USER_STACK);
56 if ((int)key >= 0) {
57 bpf_map_update_elem(&stackid_hmap, &key, &val, 0);
58 stack_p = bpf_map_lookup_elem(&stack_amap, &key);
59 if (stack_p)
60 bpf_get_stack(args, stack_p, max_len,
61 BPF_F_USER_STACK | BPF_F_USER_BUILD_ID);
62 }
63
64 return 0;
65 }
66
67 char _license[] SEC("license") = "GPL";
68