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