tools/testing/selftests/bpf/progs/exhandler_kern.c

   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 }