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<ol class="chapter"><li class="chapter-item expanded affix "><li class="part-title">eBPF 实践教程:基于 libbpf 和 CO-RE</li><li class="chapter-item expanded "><a href="../0-introduce/index.html"><strong aria-hidden="true">1.</strong> 介绍 eBPF 的基本概念、常见的开发工具</a></li><li class="chapter-item expanded "><a href="../1-helloworld/index.html"><strong aria-hidden="true">2.</strong> eBPF Hello World,基本框架和开发流程</a></li><li class="chapter-item expanded "><a href="../2-kprobe-unlink/index.html"><strong aria-hidden="true">3.</strong> 使用 kprobe 监测捕获 unlink 系统调用</a></li><li class="chapter-item expanded "><a href="../3-fentry-unlink/index.html"><strong aria-hidden="true">4.</strong> 使用 fentry 监测捕获 unlink 系统调用</a></li><li class="chapter-item expanded "><a href="../4-opensnoop/index.html" class="active"><strong aria-hidden="true">5.</strong> 捕获进程打开文件的系统调用集合,使用全局变量过滤进程 pid</a></li><li class="chapter-item expanded "><a href="../5-uprobe-bashreadline/index.html"><strong aria-hidden="true">6.</strong> 使用 uprobe 捕获 bash 的 readline 函数调用</a></li><li class="chapter-item expanded "><a href="../6-sigsnoop/index.html"><strong aria-hidden="true">7.</strong> 捕获进程发送信号的系统调用集合,使用 hash map 保存状态</a></li><li class="chapter-item expanded "><a href="../7-execsnoop/index.html"><strong aria-hidden="true">8.</strong> 捕获进程执行/退出时间,通过 perf event array 向用户态打印输出</a></li><li class="chapter-item expanded "><a href="../8-exitsnoop/index.html"><strong aria-hidden="true">9.</strong> 使用 exitsnoop 监控进程退出事件,使用 ring buffer 向用户态打印输出</a></li><li class="chapter-item expanded "><a href="../9-runqlat/index.html"><strong aria-hidden="true">10.</strong> 一个 Linux 内核 BPF 程序,通过柱状图来总结调度程序运行队列延迟,显示任务等待运行在 CPU 上的时间长度</a></li><li class="chapter-item expanded "><a href="../10-hardirqs/index.html"><strong aria-hidden="true">11.</strong> 使用 hardirqs 或 softirqs 捕获中断事件</a></li><li class="chapter-item expanded "><a href="../11-bootstrap/index.html"><strong aria-hidden="true">12.</strong> 使用 bootstrap 开发用户态程序并跟踪 exec() 和 exit() 系统调用</a></li><li class="chapter-item expanded "><a href="../13-tcpconnlat/index.html"><strong aria-hidden="true">13.</strong> 使用 libbpf-bootstrap 开发程序统计 TCP 连接延时</a></li><li class="chapter-item expanded "><a href="../14-tcpstates/index.html"><strong aria-hidden="true">14.</strong> 使用 libbpf-bootstrap 记录 TCP 连接状态与 TCP RTT</a></li><li class="chapter-item expanded "><a href="../15-javagc/index.html"><strong aria-hidden="true">15.</strong> 使用 USDT 捕获用户态 Java GC 事件耗时</a></li><li class="chapter-item expanded "><a href="../16-memleak/index.html"><strong aria-hidden="true">16.</strong> 编写 eBPF 程序 Memleak 监控内存泄漏</a></li><li class="chapter-item expanded "><a href="../17-biopattern/index.html"><strong aria-hidden="true">17.</strong> 编写 eBPF 程序 Biopattern 统计随机/顺序磁盘 I/O</a></li><li class="chapter-item expanded "><a href="../18-further-reading/index.html"><strong aria-hidden="true">18.</strong> 更多的参考资料</a></li><li class="chapter-item expanded "><a href="../19-lsm-connect/index.html"><strong aria-hidden="true">19.</strong> 使用 LSM 进行安全检测防御</a></li><li class="chapter-item expanded "><a href="../20-tc/index.html"><strong aria-hidden="true">20.</strong> 使用 eBPF 进行 tc 流量控制</a></li><li class="chapter-item expanded affix "><li class="part-title">eBPF 高级特性与进阶主题</li><li class="chapter-item expanded "><a href="../22-android/index.html"><strong aria-hidden="true">21.</strong> 在 Android 上使用 eBPF 程序</a></li><li class="chapter-item expanded "><a href="../23-http/index.html"><strong aria-hidden="true">22.</strong> 使用 eBPF 追踪 HTTP 请求或其他七层协议</a></li><li class="chapter-item expanded "><a href="../29-sockops/index.html"><strong aria-hidden="true">23.</strong> 使用 sockops 加速网络请求转发</a></li><li class="chapter-item expanded "><a href="../24-hide/index.html"><strong aria-hidden="true">24.</strong> 使用 eBPF 隐藏进程或文件信息</a></li><li class="chapter-item expanded "><a href="../25-signal/index.html"><strong aria-hidden="true">25.</strong> 使用 bpf_send_signal 发送信号终止进程</a></li><li class="chapter-item expanded "><a href="../26-sudo/index.html"><strong aria-hidden="true">26.</strong> 使用 eBPF 添加 sudo 用户</a></li><li class="chapter-item expanded "><a href="../27-replace/index.html"><strong aria-hidden="true">27.</strong> 使用 eBPF 替换任意程序读取或写入的文本</a></li><li class="chapter-item expanded "><a href="../28-detach/index.html"><strong aria-hidden="true">28.</strong> BPF的生命周期:使用 Detached 模式在用户态应用退出后持续运行 eBPF 程序</a></li><li class="chapter-item expanded affix "><li class="part-title">bcc tutorial</li><li class="chapter-item expanded "><a href="../bcc-documents/kernel-versions.html"><strong aria-hidden="true">29.</strong> BPF Features by Linux Kernel Version</a></li><li class="chapter-item expanded "><a href="../bcc-documents/kernel_config.html"><strong aria-hidden="true">30.</strong> Kernel Configuration for BPF Features</a></li><li class="chapter-item expanded "><a href="../bcc-documents/reference_guide.html"><strong aria-hidden="true">31.</strong> bcc Reference Guide</a></li><li class="chapter-item expanded "><a href="../bcc-documents/special_filtering.html"><strong aria-hidden="true">32.</strong> Special Filtering</a></li><li class="chapter-item expanded "><a href="../bcc-documents/tutorial.html"><strong aria-hidden="true">33.</strong> bcc Tutorial</a></li><li class="chapter-item expanded "><a href="../bcc-documents/tutorial_bcc_python_developer.html"><strong aria-hidden="true">34.</strong> bcc Python Developer Tutorial</a></li></ol>
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<h1 id="ebpf-入门开发实践教程四在-ebpf-中捕获进程打开文件的系统调用集合使用全局变量过滤进程-pid"><a class="header" href="#ebpf-入门开发实践教程四在-ebpf-中捕获进程打开文件的系统调用集合使用全局变量过滤进程-pid">eBPF 入门开发实践教程四:在 eBPF 中捕获进程打开文件的系统调用集合,使用全局变量过滤进程 pid</a></h1>
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<p>eBPF(Extended Berkeley Packet Filter)是一种内核执行环境,它可以让用户在内核中运行一些安全的、高效的程序。它通常用于网络过滤、性能分析、安全监控等场景。eBPF 之所以强大,是因为它能够在内核运行时捕获和修改数据包或者系统调用,从而实现对操作系统行为的监控和调整。</p>
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<p>本文是 eBPF 入门开发实践教程的第四篇,主要介绍如何捕获进程打开文件的系统调用集合,并使用全局变量在 eBPF 中过滤进程 pid。</p>
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<p>在 Linux 系统中,进程与文件之间的交互是通过系统调用来实现的。系统调用是用户态程序与内核态程序之间的接口,它们允许用户态程序请求内核执行特定操作。在本教程中,我们关注的是 sys_openat 系统调用,它是用于打开文件的。</p>
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<p>当进程打开一个文件时,它会向内核发出 sys_openat 系统调用,并传递相关参数(例如文件路径、打开模式等)。内核会处理这个请求,并返回一个文件描述符(file descriptor),这个描述符将在后续的文件操作中用作引用。通过捕获 sys_openat 系统调用,我们可以了解进程在什么时候以及如何打开文件。</p>
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<h2 id="在-ebpf-中捕获进程打开文件的系统调用集合"><a class="header" href="#在-ebpf-中捕获进程打开文件的系统调用集合">在 eBPF 中捕获进程打开文件的系统调用集合</a></h2>
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<p>首先,我们需要编写一段 eBPF 程序来捕获进程打开文件的系统调用,具体实现如下:</p>
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<pre><code class="language-c">#include <vmlinux.h>
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#include <bpf/bpf_helpers.h>
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/// @description "Process ID to trace"
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const volatile int pid_target = 0;
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SEC("tracepoint/syscalls/sys_enter_openat")
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int tracepoint__syscalls__sys_enter_openat(struct trace_event_raw_sys_enter* ctx)
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{
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u64 id = bpf_get_current_pid_tgid();
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u32 pid = id;
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if (pid_target && pid_target != pid)
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return false;
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// Use bpf_printk to print the process information
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bpf_printk("Process ID: %d enter sys openat\n", pid);
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return 0;
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}
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/// "Trace open family syscalls."
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char LICENSE[] SEC("license") = "GPL";
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</code></pre>
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<p>这段 eBPF 程序实现了:</p>
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<ol>
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<li>引入头文件:<vmlinux.h> 包含了内核数据结构的定义,<bpf/bpf_helpers.h> 包含了 eBPF 程序所需的辅助函数。</li>
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<li>定义全局变量 pid_target,用于过滤指定进程 ID。这里设为 0 表示捕获所有进程的 sys_openat 调用。</li>
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<li>使用 SEC 宏定义一个 eBPF 程序,关联到 tracepoint "tracepoint/syscalls/sys_enter_openat"。这个 tracepoint 会在进程发起 sys_openat 系统调用时触发。</li>
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<li>实现 eBPF 程序 tracepoint__syscalls__sys_enter_openat,它接收一个类型为 struct trace_event_raw_sys_enter 的参数 ctx。这个结构体包含了关于系统调用的信息。</li>
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<li>使用 bpf_get_current_pid_tgid() 函数获取当前进程的 PID 和 TGID(线程组 ID)。由于我们只关心 PID,所以将其赋值给 u32 类型的变量 pid。</li>
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<li>检查 pid_target 变量是否与当前进程的 pid 相等。如果 pid_target 不为 0 且与当前进程的 pid 不相等,则返回 false,不对该进程的 sys_openat 调用进行捕获。</li>
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<li>使用 bpf_printk() 函数打印捕获到的进程 ID 和 sys_openat 调用的相关信息。这些信息将在用户空间通过 BPF 工具查看。</li>
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<li>将程序许可证设置为 "GPL",这是运行 eBPF 程序的必要条件。</li>
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</ol>
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<p>这个 eBPF 程序可以通过 libbpf 或 eunomia-bpf 等工具加载到内核并执行。它将捕获指定进程(或所有进程)的 sys_openat 系统调用,并在用户空间输出相关信息。</p>
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<p>eunomia-bpf 是一个结合 Wasm 的开源 eBPF 动态加载运行时和开发工具链,它的目的是简化 eBPF 程序的开发、构建、分发、运行。可以参考 <a href="https://github.com/eunomia-bpf/eunomia-bpf">https://github.com/eunomia-bpf/eunomia-bpf</a> 下载和安装 ecc 编译工具链和 ecli 运行时。我们使用 eunomia-bpf 编译运行这个例子。</p>
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<p>编译运行上述代码:</p>
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<pre><code class="language-console">$ ecc opensnoop.bpf.c
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Compiling bpf object...
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Packing ebpf object and config into package.json...
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$ sudo ecli run package.json
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Runing eBPF program...
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</code></pre>
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<p>运行这段程序后,可以通过查看 /sys/kernel/debug/tracing/trace_pipe 文件来查看 eBPF 程序的输出:</p>
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<pre><code class="language-console">$ sudo cat /sys/kernel/debug/tracing/trace_pipe
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<...>-3840345 [010] d... 3220701.101179: bpf_trace_printk: Process ID: 3840345 enter sys openat
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<...>-3840345 [010] d... 3220702.158000: bpf_trace_printk: Process ID: 3840345 enter sys openat
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</code></pre>
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<p>此时,我们已经能够捕获进程打开文件的系统调用了。</p>
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<h2 id="使用全局变量在-ebpf-中过滤进程-pid"><a class="header" href="#使用全局变量在-ebpf-中过滤进程-pid">使用全局变量在 eBPF 中过滤进程 pid</a></h2>
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<p>全局变量在 eBPF 程序中充当一种数据共享机制,它们允许用户态程序与 eBPF 程序之间进行数据交互。这在过滤特定条件或修改 eBPF 程序行为时非常有用。这种设计使得用户态程序能够在运行时动态地控制 eBPF 程序的行为。</p>
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<p>在我们的例子中,全局变量 <code>pid_target</code> 用于过滤进程 PID。用户态程序可以设置此变量的值,以便在 eBPF 程序中只捕获与指定 PID 相关的 <code>sys_openat</code> 系统调用。</p>
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<p>使用全局变量的原理是,全局变量在 eBPF 程序的数据段(data section)中定义并存储。当 eBPF 程序加载到内核并执行时,这些全局变量会保持在内核中,可以通过 BPF 系统调用进行访问。用户态程序可以使用 BPF 系统调用中的某些特性,如 bpf_obj_get_info_by_fd 和 bpf_obj_get_info,获取 eBPF 对象的信息,包括全局变量的位置和值。</p>
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<p>可以通过执行 ecli -h 命令来查看 opensnoop 的帮助信息:</p>
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<pre><code class="language-console">$ ecli package.json -h
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Usage: opensnoop_bpf [--help] [--version] [--verbose] [--pid_target VAR]
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Trace open family syscalls.
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Optional arguments:
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-h, --help shows help message and exits
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-v, --version prints version information and exits
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--verbose prints libbpf debug information
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--pid_target Process ID to trace
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Built with eunomia-bpf framework.
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See https://github.com/eunomia-bpf/eunomia-bpf for more information.
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</code></pre>
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<p>可以通过 --pid_target 参数来指定要捕获的进程的 pid,例如:</p>
|
||
<pre><code class="language-console">$ sudo ./ecli run package.json --pid_target 618
|
||
Runing eBPF program...
|
||
</code></pre>
|
||
<p>运行这段程序后,可以通过查看 /sys/kernel/debug/tracing/trace_pipe 文件来查看 eBPF 程序的输出:</p>
|
||
<pre><code class="language-console">$ sudo cat /sys/kernel/debug/tracing/trace_pipe
|
||
<...>-3840345 [010] d... 3220701.101179: bpf_trace_printk: Process ID: 618 enter sys openat
|
||
<...>-3840345 [010] d... 3220702.158000: bpf_trace_printk: Process ID: 618 enter sys openat
|
||
</code></pre>
|
||
<h2 id="总结"><a class="header" href="#总结">总结</a></h2>
|
||
<p>本文介绍了如何使用 eBPF 程序来捕获进程打开文件的系统调用。在 eBPF 程序中,我们可以通过定义 tracepoint__syscalls__sys_enter_open 和 tracepoint__syscalls__sys_enter_openat 函数并使用 SEC 宏把它们附加到 sys_enter_open 和 sys_enter_openat 两个 tracepoint 来捕获进程打开文件的系统调用。我们可以使用 bpf_get_current_pid_tgid 函数获取调用 open 或 openat 系统调用的进程 ID,并使用 bpf_printk 函数在内核日志中打印出来。在 eBPF 程序中,我们还可以通过定义一个全局变量 pid_target 来指定要捕获的进程的 pid,从而过滤输出,只输出指定的进程的信息。</p>
|
||
<p>通过学习本教程,您应该对如何在 eBPF 中捕获和过滤特定进程的系统调用有了更深入的了解。这种方法在系统监控、性能分析和安全审计等场景中具有广泛的应用。</p>
|
||
<p>更多的例子和详细的开发指南,请参考 eunomia-bpf 的官方文档:<a href="https://github.com/eunomia-bpf/eunomia-bpf">https://github.com/eunomia-bpf/eunomia-bpf</a></p>
|
||
<p>如果您希望学习更多关于 eBPF 的知识和实践,可以访问我们的教程代码仓库 <a href="https://github.com/eunomia-bpf/bpf-developer-tutorial">https://github.com/eunomia-bpf/bpf-developer-tutorial</a> 以获取更多示例和完整的教程。</p>
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