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