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<ol class="chapter"><li class="chapter-item expanded affix "><a href="../https://github.com/eunomia-bpf/bpf-developer-tutorial.html">https://github.com/eunomia-bpf/bpf-developer-tutorial</a></li><li class="chapter-item expanded affix "><li class="part-title">目录</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"><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" class="active"><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="../30-sslsniff/index.html"><strong aria-hidden="true">23.</strong> 使用 uprobe 捕获多种库的 SSL/TLS 明文数据</a></li><li class="chapter-item expanded "><a href="../29-sockops/index.html"><strong aria-hidden="true">24.</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">25.</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">26.</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">27.</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">28.</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">29.</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 "><a href="../30-sslsniff/index.html"><strong aria-hidden="true">30.</strong> 使用 eBPF 用户态捕获多种库的 SSL/TLS 明文数据</a></li><li class="chapter-item expanded affix "><li class="part-title">bcc 教程与文档</li><li class="chapter-item expanded "><a href="../bcc-documents/kernel-versions.html"><strong aria-hidden="true">31.</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">32.</strong> Kernel Configuration for BPF Features</a></li><li class="chapter-item expanded "><a href="../bcc-documents/reference_guide.html"><strong aria-hidden="true">33.</strong> bcc Reference Guide</a></li><li class="chapter-item expanded "><a href="../bcc-documents/special_filtering.html"><strong aria-hidden="true">34.</strong> Special Filtering</a></li><li class="chapter-item expanded "><a href="../bcc-documents/tutorial.html"><strong aria-hidden="true">35.</strong> bcc Tutorial</a></li><li class="chapter-item expanded "><a href="../bcc-documents/tutorial_bcc_python_developer.html"><strong aria-hidden="true">36.</strong> bcc Python Developer Tutorial</a></li></ol>
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<h1 id="ebpf-入门开发实践教程五在-ebpf-中使用--uprobe-捕获-bash-的-readline-函数调用"><a class="header" href="#ebpf-入门开发实践教程五在-ebpf-中使用--uprobe-捕获-bash-的-readline-函数调用">eBPF 入门开发实践教程五：在 eBPF 中使用 uprobe 捕获 bash 的 readline 函数调用</a></h1>
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<p>eBPF (Extended Berkeley Packet Filter) 是 Linux 内核上的一个强大的网络和性能分析工具，它允许开发者在内核运行时动态加载、更新和运行用户定义的代码。</p>
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<p>本文是 eBPF 入门开发实践教程的第五篇，主要介绍如何使用 uprobe 捕获 bash 的 readline 函数调用。</p>
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<h2 id="什么是uprobe"><a class="header" href="#什么是uprobe">什么是uprobe</a></h2>
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<p>uprobe是一种用户空间探针，uprobe探针允许在用户空间程序中动态插桩，插桩位置包括：函数入口、特定偏移处，以及函数返回处。当我们定义uprobe时，内核会在附加的指令上创建快速断点指令（x86机器上为int3指令），当程序执行到该指令时，内核将触发事件，程序陷入到内核态，并以回调函数的方式调用探针函数，执行完探针函数再返回到用户态继续执行后序的指令。</p>
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<p>uprobe基于文件，当一个二进制文件中的一个函数被跟踪时，所有使用到这个文件的进程都会被插桩，包括那些尚未启动的进程，这样就可以在全系统范围内跟踪系统调用。</p>
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<p>uprobe适用于在用户态去解析一些内核态探针无法解析的流量，例如http2流量（报文header被编码，内核无法解码），https流量（加密流量，内核无法解密）。</p>
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<h2 id="使用-uprobe-捕获-bash-的-readline-函数调用"><a class="header" href="#使用-uprobe-捕获-bash-的-readline-函数调用">使用 uprobe 捕获 bash 的 readline 函数调用</a></h2>
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<p>uprobe 是一种用于捕获用户空间函数调用的 eBPF 的探针，我们可以通过它来捕获用户空间程序调用的系统函数。</p>
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<p>例如，我们可以使用 uprobe 来捕获 bash 的 readline 函数调用，从而获取用户在 bash 中输入的命令行。示例代码如下：</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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#include <bpf/bpf_tracing.h>
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#define TASK_COMM_LEN 16
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#define MAX_LINE_SIZE 80
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/* Format of u[ret]probe section definition supporting auto-attach:
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* u[ret]probe/binary:function[+offset]
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*
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* binary can be an absolute/relative path or a filename; the latter is resolved to a
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* full binary path via bpf_program__attach_uprobe_opts.
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*
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* Specifying uprobe+ ensures we carry out strict matching; either "uprobe" must be
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* specified (and auto-attach is not possible) or the above format is specified for
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* auto-attach.
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*/
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SEC("uretprobe//bin/bash:readline")
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int BPF_KRETPROBE(printret, const void *ret)
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{
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char str[MAX_LINE_SIZE];
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char comm[TASK_COMM_LEN];
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u32 pid;
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if (!ret)
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return 0;
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bpf_get_current_comm(&comm, sizeof(comm));
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pid = bpf_get_current_pid_tgid() >> 32;
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bpf_probe_read_user_str(str, sizeof(str), ret);
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bpf_printk("PID %d (%s) read: %s ", pid, comm, str);
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return 0;
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};
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char LICENSE[] SEC("license") = "GPL";
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</code></pre>
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<p>这段代码的作用是在 bash 的 readline 函数返回时执行指定的 BPF_KRETPROBE 函数，即 printret 函数。</p>
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<p>在 printret 函数中，我们首先获取了调用 readline 函数的进程的进程名称和进程 ID，然后通过 bpf_probe_read_user_str 函数读取了用户输入的命令行字符串，最后通过 bpf_printk 函数打印出进程 ID、进程名称和输入的命令行字符串。</p>
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<p>除此之外，我们还需要通过 SEC 宏来定义 uprobe 探针，并使用 BPF_KRETPROBE 宏来定义探针函数。</p>
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<p>在 SEC 宏中，我们需要指定 uprobe 的类型、要捕获的二进制文件的路径和要捕获的函数名称。例如，上面的代码中的 SEC 宏的定义如下：</p>
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<pre><code class="language-c">SEC("uprobe//bin/bash:readline")
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</code></pre>
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<p>这表示我们要捕获的是 /bin/bash 二进制文件中的 readline 函数。</p>
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<p>接下来，我们需要使用 BPF_KRETPROBE 宏来定义探针函数，例如：</p>
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<pre><code class="language-c">BPF_KRETPROBE(printret, const void *ret)
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</code></pre>
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<p>这里的 printret 是探针函数的名称，const void *ret 是探针函数的参数，它代表被捕获的函数的返回值。</p>
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<p>然后，我们使用了 bpf_get_current_comm 函数获取当前任务的名称，并将其存储在 comm 数组中。</p>
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<pre><code class="language-c"> bpf_get_current_comm(&comm, sizeof(comm));
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</code></pre>
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<p>使用 bpf_get_current_pid_tgid 函数获取当前进程的 PID，并将其存储在 pid 变量中。</p>
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<pre><code class="language-c"> pid = bpf_get_current_pid_tgid() >> 32;
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</code></pre>
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<p>使用 bpf_probe_read_user_str 函数从用户空间读取 readline 函数的返回值，并将其存储在 str 数组中。</p>
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<pre><code class="language-c"> bpf_probe_read_user_str(str, sizeof(str), ret);
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</code></pre>
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<p>最后使用 bpf_printk 函数输出 PID、任务名称和用户输入的字符串。</p>
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<pre><code class="language-c"> bpf_printk("PID %d (%s) read: %s ", pid, comm, str);
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</code></pre>
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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>
|
||
<p>编译运行上述代码：</p>
|
||
<pre><code class="language-console">$ ecc bashreadline.bpf.c
|
||
Compiling bpf object...
|
||
Packing ebpf object and config into package.json...
|
||
$ sudo ecli run package.json
|
||
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
|
||
bash-32969 [000] d..31 64001.375748: bpf_trace_printk: PID 32969 (bash) read: fff
|
||
bash-32969 [000] d..31 64002.056951: bpf_trace_printk: PID 32969 (bash) read: fff
|
||
</code></pre>
|
||
<p>可以看到，我们成功的捕获了 bash 的 readline 函数调用，并获取了用户在 bash 中输入的命令行。</p>
|
||
<h2 id="总结"><a class="header" href="#总结">总结</a></h2>
|
||
<p>在上述代码中，我们使用了 SEC 宏来定义了一个 uprobe 探针，它指定了要捕获的用户空间程序 (bin/bash) 和要捕获的函数 (readline)。此外，我们还使用了 BPF_KRETPROBE 宏来定义了一个用于处理 readline 函数返回值的回调函数 (printret)。该函数可以获取到 readline 函数的返回值，并将其打印到内核日志中。通过这样的方式，我们就可以使用 eBPF 来捕获 bash 的 readline 函数调用，并获取用户在 bash 中输入的命令行。</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> 或网站 <a href="https://eunomia.dev/zh/tutorials/">https://eunomia.dev/zh/tutorials/</a> 以获取更多示例和完整的教程。</p>
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