1// SPDX-License-Identifier: GPL-2.0
2/* Copyright (c) 2021 Google */
3
4#include "vmlinux.h"
5
6#include <bpf/bpf_helpers.h>
7
8extern const int bpf_prog_active __ksym; /* int type global var. */
9
10SEC("raw_tp/sys_enter")
11int handler1(const void *ctx)
12{
13 int *active;
14 __u32 cpu;
15
16 cpu = bpf_get_smp_processor_id();
17 active = (int *)bpf_per_cpu_ptr(&bpf_prog_active, cpu);
18 if (active) {
19 /* Kernel memory obtained from bpf_{per,this}_cpu_ptr
20 * is read-only, should _not_ pass verification.
21 */
22 /* WRITE_ONCE */
23 *(volatile int *)active = -1;
24 }
25
26 return 0;
27}
28
29__noinline int write_active(int *p)
30{
31 return p ? (*p = 42) : 0;
32}
33
34SEC("raw_tp/sys_enter")
35int handler2(const void *ctx)
36{
37 int *active;
38
39 active = bpf_this_cpu_ptr(&bpf_prog_active);
40 write_active(active);
41 return 0;
42}
43
44char _license[] SEC("license") = "GPL";
45

source code of linux/tools/testing/selftests/bpf/progs/test_ksyms_btf_write_check.c