1 // SPDX-License-Identifier: GPL-2.0
2 /* Copyright (c) 2021, Oracle and/or its affiliates. */
3
4 #include "vmlinux.h"
5
6 #include <bpf/bpf_helpers.h>
7 #include <bpf/bpf_tracing.h>
8 #include <bpf/bpf_core_read.h>
9
10 char _license[] SEC("license") = "GPL";
11
12 unsigned int exception_triggered;
13 int test_pid;
14
15 /* TRACE_EVENT(task_newtask,
16 * TP_PROTO(struct task_struct *p, u64 clone_flags)
17 */
18 SEC("tp_btf/task_newtask")
19 int BPF_PROG(trace_task_newtask, struct task_struct *task, u64 clone_flags)
20 {
21 int pid = bpf_get_current_pid_tgid() >> 32;
22 struct callback_head *work;
23 void *func;
24
25 if (test_pid != pid)
26 return 0;
27
28 /* To verify we hit an exception we dereference task->task_works->func.
29 * If task work has been added,
30 * - task->task_works is non-NULL; and
31 * - task->task_works->func is non-NULL also (the callback function
32 * must be specified for the task work.
33 *
34 * However, for a newly-created task, task->task_works is NULLed,
35 * so we know the exception handler triggered if task_works is
36 * NULL and func is NULL.
37 */
38 work = task->task_works;
39 func = work->func;
40 /* Currently verifier will fail for `btf_ptr |= btf_ptr` * instruction.
41 * To workaround the issue, use barrier_var() and rewrite as below to
42 * prevent compiler from generating verifier-unfriendly code.
43 */
44 barrier_var(work);
45 if (work)
46 return 0;
47 barrier_var(func);
48 if (func)
49 return 0;
50 exception_triggered++;
51 return 0;
52 }
53
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.