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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">入门文档</li><li class="chapter-item expanded "><a href="../0-introduce/index.html"><strong aria-hidden="true">1.</strong> lesson 0-introduce</a></li><li class="chapter-item expanded "><a href="../1-helloworld/index.html"><strong aria-hidden="true">2.</strong> lesson 1-helloworld</a></li><li class="chapter-item expanded "><a href="../2-kprobe-unlink/index.html"><strong aria-hidden="true">3.</strong> lesson 2-kprobe-unlink</a></li><li class="chapter-item expanded "><a href="../3-fentry-unlink/index.html"><strong aria-hidden="true">4.</strong> lesson 3-fentry-unlink</a></li><li class="chapter-item expanded "><a href="../4-opensnoop/index.html"><strong aria-hidden="true">5.</strong> lesson 4-opensnoop</a></li><li class="chapter-item expanded "><a href="../5-uprobe-bashreadline/index.html"><strong aria-hidden="true">6.</strong> lesson 5-uprobe-bashreadline</a></li><li class="chapter-item expanded "><a href="../6-sigsnoop/index.html"><strong aria-hidden="true">7.</strong> lesson 6-sigsnoop</a></li><li class="chapter-item expanded "><a href="../7-execsnoop/index.html"><strong aria-hidden="true">8.</strong> lesson 7-execsnoop</a></li><li class="chapter-item expanded "><a href="../8-exitsnoop/index.html"><strong aria-hidden="true">9.</strong> lesson 8-execsnoop</a></li><li class="chapter-item expanded "><a href="../9-runqlat/index.html"><strong aria-hidden="true">10.</strong> lesson 9-runqlat</a></li><li class="chapter-item expanded "><a href="../10-hardirqs/index.html"><strong aria-hidden="true">11.</strong> lesson 10-hardirqs</a></li><li class="chapter-item expanded affix "><li class="part-title">进阶文档和示例</li><li class="chapter-item expanded "><a href="../11-bootstrap/index.html"><strong aria-hidden="true">12.</strong> lesson 11-bootstrap</a></li><li class="chapter-item expanded "><a href="../12-profile/index.html"><strong aria-hidden="true">13.</strong> lesson 12-profile</a></li><li class="chapter-item expanded "><a href="../13-tcpconnlat/index.html"><strong aria-hidden="true">14.</strong> lesson 13-tcpconnlat</a></li><li class="chapter-item expanded "><a href="../14-tcpstates/index.html"><strong aria-hidden="true">15.</strong> lesson 14-tcpstates</a></li><li class="chapter-item expanded "><a href="../15-javagc/index.html"><strong aria-hidden="true">16.</strong> lesson 15-javagc</a></li><li class="chapter-item expanded "><a href="../16-memleak/index.html"><strong aria-hidden="true">17.</strong> lesson 16-memleak</a></li><li class="chapter-item expanded "><a href="../17-biopattern/index.html"><strong aria-hidden="true">18.</strong> lesson 17-biopattern</a></li><li class="chapter-item expanded "><a href="../18-further-reading/index.html"><strong aria-hidden="true">19.</strong> lesson 18-further-reading</a></li><li class="chapter-item expanded "><a href="../19-lsm-connect/index.html"><strong aria-hidden="true">20.</strong> lesson 19-lsm-connect</a></li><li class="chapter-item expanded "><a href="../20-tc/index.html"><strong aria-hidden="true">21.</strong> lesson 20-tc</a></li><li class="chapter-item expanded "><a href="../21-xdp/index.html" class="active"><strong aria-hidden="true">22.</strong> lesson 21-xdp</a></li><li class="chapter-item expanded affix "><li class="part-title">高级主题</li><li class="chapter-item expanded "><a href="../22-android/index.html"><strong aria-hidden="true">23.</strong> 在 Android 上使用 eBPF 程序</a></li><li class="chapter-item expanded "><a href="../30-sslsniff/index.html"><strong aria-hidden="true">24.</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="../23-http/index.html"><strong aria-hidden="true">25.</strong> 使用 eBPF socket filter 或 syscall trace 追踪 HTTP 请求和其他七层协议</a></li><li class="chapter-item expanded "><a href="../29-sockops/index.html"><strong aria-hidden="true">26.</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">27.</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">28.</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">29.</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">30.</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">31.</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="../18-further-reading/ebpf-security.zh.html"><strong aria-hidden="true">32.</strong> eBPF 运行时的安全性与面临的挑战</a></li><li class="chapter-item expanded "><a href="../34-syscall/index.html"><strong aria-hidden="true">33.</strong> 使用 eBPF 修改系统调用参数</a></li><li class="chapter-item expanded "><a href="../36-userspace-ebpf/index.html"><strong aria-hidden="true">34.</strong> 用户空间 eBPF 运行时：深度解析与应用实践</a></li><li class="chapter-item expanded affix "><li class="part-title">bcc 和 bpftrace 教程与文档</li><li class="chapter-item expanded "><a href="../bcc-documents/kernel-versions.html"><strong aria-hidden="true">35.</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">36.</strong> Kernel Configuration for BPF Features</a></li><li class="chapter-item expanded "><a href="../bcc-documents/reference_guide.html"><strong aria-hidden="true">37.</strong> bcc Reference Guide</a></li><li class="chapter-item expanded "><a href="../bcc-documents/special_filtering.html"><strong aria-hidden="true">38.</strong> Special Filtering</a></li><li class="chapter-item expanded "><a href="../bcc-documents/tutorial.html"><strong aria-hidden="true">39.</strong> bcc Tutorial</a></li><li class="chapter-item expanded "><a href="../bcc-documents/tutorial_bcc_python_developer.html"><strong aria-hidden="true">40.</strong> bcc Python Developer Tutorial</a></li><li class="chapter-item expanded "><a href="../bpftrace-tutorial/index.html"><strong aria-hidden="true">41.</strong> bpftrace Tutorial</a></li></ol>
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<h1 id="ebpf-入门实践教程二十一使用-xdp-实现可编程包处理"><a class="header" href="#ebpf-入门实践教程二十一使用-xdp-实现可编程包处理">eBPF 入门实践教程二十一：使用 xdp 实现可编程包处理</a></h1>
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<h2 id="背景"><a class="header" href="#背景">背景</a></h2>
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<p>xdp（eXpress Data Path）是 Linux 内核中新兴的一种绕过内核的、可编程的包处理方案。相较于 cBPF，xdp 的挂载点非常底层，位于网络设备驱动的软中断处理过程，甚至早于 skb_buff 结构的分配。因此，在 xdp 上挂载 eBPF 程序适用于很多简单但次数极多的包处理操作（如防御 Dos 攻击），可以达到很高的性能（24Mpps/core）。</p>
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<h2 id="xdp-概述"><a class="header" href="#xdp-概述">XDP 概述</a></h2>
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<p>xdp 不是第一个支持可编程包处理的系统，在此之前，以 DPDK（Data Plane Development Kit）为代表的内核旁路方案甚至能够取得更高的性能，其思路为完全绕过内核，由用户态的网络应用接管网络设备，从而避免了用户态和内核态的切换开销。然而，这样的方式具有很多天然的缺陷：</p>
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<ul>
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<li>无法与内核中成熟的网络模块集成，而不得不在用户态将其重新实现；</li>
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<li>破坏了内核的安全边界，使得内核提供的很多网络工具变得不可用；</li>
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<li>在与常规的 socket 交互时，需要从用户态重新将包注入到内核；</li>
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<li>需要占用一个或多个单独的 CPU 来进行包处理；</li>
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</ul>
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<p>除此之外，利用内核模块和内核网络协议栈中的 hook 点也是一种思路，然而前者对内核的改动大，出错的代价高昂；后者在整套包处理流程中位置偏后，其效率不够理想。</p>
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<p>总而言之，xdp + eBPF 为可编程包处理系统提出了一种更为稳健的思路，在某种程度上权衡了上述方案的种种优点和不足，获取较高性能的同时又不会对内核的包处理流程进行过多的改变，同时借助 eBPF 虚拟机的优势将用户定义的包处理过程进行隔离和限制，提高了安全性。</p>
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<h2 id="编写-ebpf-程序"><a class="header" href="#编写-ebpf-程序">编写 eBPF 程序</a></h2>
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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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/// @ifindex 1
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/// @flags 0
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/// @xdpopts {"old_prog_fd":0}
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SEC("xdp")
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int xdp_pass(struct xdp_md* ctx) {
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void* data = (void*)(long)ctx->data;
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void* data_end = (void*)(long)ctx->data_end;
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int pkt_sz = data_end - data;
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bpf_printk("packet size is %d", pkt_sz);
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return XDP_PASS;
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}
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char __license[] SEC("license") = "GPL";
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</code></pre>
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<p>这是一段 C 语言实现的 eBPF 内核侧代码，它能够通过 xdp 捕获所有经过目标网络设备的数据包，计算其大小并输出到 <code>trace_pipe</code> 中。</p>
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<p>值得注意的是，在代码中我们使用了以下注释：</p>
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<pre><code class="language-C">/// @ifindex 1
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/// @flags 0
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/// @xdpopts {"old_prog_fd":0}
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</code></pre>
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<p>这是由 eunomia-bpf 提供的功能，我们可以通过这样的注释告知 eunomia-bpf 加载器此 xdp 程序想要挂载的目标网络设备编号，挂载的标志和选项。</p>
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<p>这些变量的设计基于 libbpf 提供的 API，可以通过 <a href="https://patchwork.kernel.org/project/netdevbpf/patch/20220120061422.2710637-2-andrii@kernel.org/#24705508">patchwork</a> 查看接口的详细介绍。</p>
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<p><code>SEC("xdp")</code> 宏指出 BPF 程序的类型，<code>ctx</code> 是此 BPF 程序执行的上下文，用于包处理流程。</p>
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<p>在程序的最后，我们返回了 <code>XDP_PASS</code>，这表示我们的 xdp 程序会将经过目标网络设备的包正常交付给内核的网络协议栈。可以通过 <a href="https://prototype-kernel.readthedocs.io/en/latest/networking/XDP/implementation/xdp_actions.html">XDP actions</a> 了解更多 xdp 的处理动作。</p>
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<h2 id="编译运行"><a class="header" href="#编译运行">编译运行</a></h2>
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<p>通过容器编译：</p>
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<pre><code class="language-console">docker run -it -v `pwd`/:/src/ ghcr.io/eunomia-bpf/ecc-`uname -m`:latest
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</code></pre>
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<p>或是通过 <code>ecc</code> 编译：</p>
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<pre><code class="language-console">$ ecc xdp.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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</code></pre>
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<p>并通过 <code>ecli</code> 运行：</p>
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<pre><code class="language-console">sudo ecli run package.json
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</code></pre>
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<p>可以通过如下方式查看程序的输出：</p>
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<pre><code class="language-console">$ sudo cat /sys/kernel/tracing/trace_pipe
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node-1939 [000] d.s11 1601.190413: bpf_trace_printk: packet size is 177
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node-1939 [000] d.s11 1601.190479: bpf_trace_printk: packet size is 66
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ksoftirqd/1-19 [001] d.s.1 1601.237507: bpf_trace_printk: packet size is 66
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node-1939 [000] d.s11 1601.275860: bpf_trace_printk: packet size is 344
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</code></pre>
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<h2 id="总结"><a class="header" href="#总结">总结</a></h2>
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<p>本文介绍了如何使用 xdp 来处理经过特定网络设备的包，基于 eunomia-bpf 提供的通过注释向 libbpf 传递参数的方案，我们可以将自己编写的 xdp BPF 程序以指定选项挂载到目标设备，并在网络包进入内核网络协议栈之前就对其进行处理，从而获取高性能的可编程包处理能力。</p>
|
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<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>
|
||
<h2 id="参考资料"><a class="header" href="#参考资料">参考资料</a></h2>
|
||
<ul>
|
||
<li><a href="http://arthurchiao.art/blog/xdp-paper-acm-2018-zh/">http://arthurchiao.art/blog/xdp-paper-acm-2018-zh/</a></li>
|
||
<li><a href="http://arthurchiao.art/blog/linux-net-stack-implementation-rx-zh/">http://arthurchiao.art/blog/linux-net-stack-implementation-rx-zh/</a></li>
|
||
<li><a href="https://github.com/xdp-project/xdp-tutorial/tree/master/basic01-xdp-pass">https://github.com/xdp-project/xdp-tutorial/tree/master/basic01-xdp-pass</a></li>
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