f760d05379
Add barrier() and barrier_var() macros into bpf_helpers.h to be used by end users. While a bit advanced and specialized instruments, they are sometimes indispensable. Instead of requiring each user to figure out exact asm volatile incantations for themselves, provide them from bpf_helpers.h. Also remove conflicting definitions from selftests. Some tests rely on barrier_var() definition being nothing, those will still work as libbpf does the #ifndef/#endif guarding for barrier() and barrier_var(), allowing users to redefine them, if necessary. Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20220509004148.1801791-8-andrii@kernel.org
52 lines
1.4 KiB
C
52 lines
1.4 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2021, Oracle and/or its affiliates. */
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#include "vmlinux.h"
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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#include <bpf/bpf_core_read.h>
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char _license[] SEC("license") = "GPL";
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unsigned int exception_triggered;
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int test_pid;
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/* TRACE_EVENT(task_newtask,
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* TP_PROTO(struct task_struct *p, u64 clone_flags)
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*/
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SEC("tp_btf/task_newtask")
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int BPF_PROG(trace_task_newtask, struct task_struct *task, u64 clone_flags)
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{
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int pid = bpf_get_current_pid_tgid() >> 32;
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struct callback_head *work;
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void *func;
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if (test_pid != pid)
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return 0;
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/* To verify we hit an exception we dereference task->task_works->func.
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* If task work has been added,
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* - task->task_works is non-NULL; and
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* - task->task_works->func is non-NULL also (the callback function
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* must be specified for the task work.
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*
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* However, for a newly-created task, task->task_works is NULLed,
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* so we know the exception handler triggered if task_works is
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* NULL and func is NULL.
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*/
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work = task->task_works;
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func = work->func;
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/* Currently verifier will fail for `btf_ptr |= btf_ptr` * instruction.
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* To workaround the issue, use barrier_var() and rewrite as below to
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* prevent compiler from generating verifier-unfriendly code.
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*/
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barrier_var(work);
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if (work)
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return 0;
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barrier_var(func);
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if (func)
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return 0;
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exception_triggered++;
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return 0;
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}
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