Linux内核功能eBPF入门学习（一）：BPF、eBPF、BCC等基本概念

红太狼 2022-11-27 05:23 340阅读 0赞

Linux内核观测技术BP

[https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html][https_www.lijiaocn.com_E6_8A_80_E5_B7_A7_2019_02_25_ebpf-introduction-1.html]

## 目录 ##

*  [目录][Link 1]
 *  [说明][Link 2]
 *  [BPF][]
 *  [eBPF带来的新变化][eBPF]
 *  [eBPF使用][eBPF 1]
    
     *  [升级内核][Link 3]
     *  [eBPF代码示例][eBPF 2]
     *  [eBPF代码编译装载][eBPF 3]
 *  [使用BCC简化eBPF应用开发过程][BCC_eBPF]
    
     *  [BCC安装][BCC]
     *  [BCC收集的eBPF应用][BCC_eBPF 1]
 *  [参考][Link 4]

## 说明 ##

eBPF是kernel 3.15中引入的全新设计，将原先的BPF发展成一个指令集更复杂、应用范围更广的“内核虚拟机”。

eBPF支持在用户态将C语言编写的一小段“内核代码”注入到内核中运行，注入时要先用llvm编译得到使用BPF指令集的elf文件，然后从elf文件中解析出可以注入内核的部分，最后用bpf\_load\_program方法完成注入。 用户态程序和注入到内核中的程序通过共用一个位于内核中`map`实现通信。为了防止注入的代码导致内核崩溃，eBPF会对注入的代码进行严格检查，拒绝不合格的代码的注入。

[BCC][BCC 1]是一个python库，实现了map创建、代码编译、解析、注入等操作，使开发人员只需聚焦于用C语言开发要注入的内核代码。 文章[eBPF简史][eBPF 4]从eBPF的前身BPF讲起，将eBPF的来龙去脉介绍的很明白，是难得的好文章，建议直接过去阅读，这里就不摘抄了。 [BPF: the universal in-kernel virtual machine][BPF_ the universal in-kernel virtual machine]介绍了BPF从网络子系统中的报文复制功能到内核通用虚拟机eBPF的演变过程。

## BPF ##

BPF是很早就有的内核特性，在内核中将报文“镜像”了一份，并用BPF指令检查镜像出来的报文、决定报文的去留，即在1)抛弃报文和2)将其复制到用户空间之间抉择。

具体实现就不去了解了，BPF好歹设计了一套指令集，虽然比较简单，但没有扎实的编译原理基础，估计一时半会儿也看不懂，这里只收集一下相关文档：

1.  [The BSD Packet Filter: A New Architecture for User-level Packet Capture][The BSD Packet Filter_ A New Architecture for User-level Packet Capture]
2.  [Kernel Documentation：BPF Documentation][Kernel Documentation_BPF Documentation]
3.  [Linux Socket Filtering aka Berkeley Packet Filter (BPF)][Linux Socket Filtering aka Berkeley Packet Filter _BPF]

另外学到了一个新知识，tcpdump使用的libpcap是基于BPF的，在使用tcpdump或者libpcap时传入的“host 192.168.1.1”、“tcp and port 80”等是`过滤表达式`。

过滤表达式会被编译成`BPF指令`，在tcpdump命令后面加上`-d`参数可以看到：

$ tcpdump -d -i eth0 tcp and port 80
    (000) ldh      [12]
    (001) jeq      #0x86dd          jt 2	jf 8
    (002) ldb      [20]
    (003) jeq      #0x6             jt 4	jf 19
    (004) ldh      [54]
    (005) jeq      #0x50            jt 18	jf 6
    (006) ldh      [56]
    (007) jeq      #0x50            jt 18	jf 19
    (008) jeq      #0x800           jt 9	jf 19
    (009) ldb      [23]
    (010) jeq      #0x6             jt 11	jf 19
    (011) ldh      [20]
    (012) jset     #0x1fff          jt 19	jf 13
    (013) ldxb     4*([14]&0xf)
    (014) ldh      [x + 14]
    (015) jeq      #0x50            jt 18	jf 16
    (016) ldh      [x + 16]
    (017) jeq      #0x50            jt 18	jf 19
    (018) ret      #65535
    (019) ret      #0

这些BPF指令是在内核中被BPF解释执行的。

## eBPF带来的新变化 ##

原先的BPF依然支持，用cBPF指代。eBPF全新设计了更丰富的指令集、增加了寄存器，性能大幅提高：

> The original patch that added support for eBPF in the 3.15 kernel showed that eBPF was up to four times faster on x86-64 than the old classic BPF (cBPF) implementation for some network filter microbenchmarks, and most were 1.5 times faster.

增加了名为`bpf`的系统调用，为用户态程序提供与内核中的eBPF进行交互的途径：

int bpf(int cmd, union bpf_attr *attr, unsigned int size);

`cmd`是eBPF支持的cmd，分为三类： 操作注入的代码、操作用于通信的map、前两个操作的混合。

通过eBPF可以做更多的事情，不再仅仅是进行报文复制和过滤，网络方面可以切入到更深的层次，在更“靠前”的阶段进行干预，例如[XDP][]借助eBPF在报文刚收到的时候就进行干预，[使用XDP(eXpress Data Path)防御DDoS攻击][XDP_eXpress Data Path_DDoS]。

还可以：

1.  限制进程可以使用的系统调用，[seccomp][];
2.  输出内核中的数据，进行内核调试、性能分析、调用跟踪；
3.  调试用户态程序，[Userland Statically Defined Tracepoints ][Userland Statically Defined Tracepoints]；

## eBPF使用 ##

eBPF是kernel 3.15开始支持的，在kernel 3.17源码中获得了一个单独的bpf目录，建议直接使用3.17以及以上版本的内核。下面这四篇文章可以帮你搭建对eBPF的认知框架：

1.  [LWN.net: A thorough introduction to eBPF][LWN.net_ A thorough introduction to eBPF]
2.  [LWN.net: An introduction to the BPF Compiler Collection][LWN.net_ An introduction to the BPF Compiler Collection]
3.  [LWN.net: Some advanced BCC topics][LWN.net_ Some advanced BCC topics]
4.  [LWN.net: Using user-space tracepoints with BPF][LWN.net_ Using user-space tracepoints with BPF]

### 升级内核 ###

见：[CentOS7/6内核升级的简单方法：借助ELRepo，用yum命令更新内核][CentOS7_6_ELRepo_yum]。

### eBPF代码示例 ###

[samples/bpf][samples_bpf]，暂时没有找到相关资料，目前以学习bcc的使用为主，2019-02-25 18:11:40

### eBPF代码编译装载 ###

同上一节。

## 使用BCC简化eBPF应用开发过程 ##

[BCC][BCC 1]首先提供了一个名为bcc的python库，简化了eBPF应用的开发过程，然后它收集大量的eBPF应用，主要是性能分析相关的。 可以直接使用bcc已经收集的命令调查问题（[bcc Tutorial][]），也可以用bcc提供的python库自己开发eBPF应用（[bcc Python Developer Tutorial][]）。

Kernel版本需要是4.1以上（2019-02-25 18:08:15），并且要安装kernel-devel，如果没有安装kernel-devel，eBPF应用会汇编译失败（bcc收集的命令运行时也会出现下面错误）：

# execsnoop
    chdir(/lib/modules/4.20.12-1.el7.elrepo.x86_64/build): No such file or directory
    Traceback (most recent call last):
      File "/usr/share/bcc/tools/execsnoop", line 166, in <module>
        b = BPF(text=bpf_text)
      File "/usr/lib/python2.7/site-packages/bcc/__init__.py", line 318, in __init__
        raise Exception("Failed to compile BPF text")
    Exception: Failed to compile BPF text

### BCC安装 ###

直接用yum安装：

yum install bcc-tools

用`rpm -ql`可以看到所有bcc文件，`tools/`目录中是bcc提供的命令，可以用`man`查看对应的手册，比如`man bcc-argdist`：

$ rpm -ql bcc-tools
    /usr/share/bcc
    /usr/share/bcc/introspection
    /usr/share/bcc/introspection/bps
    /usr/share/bcc/tools
    /usr/share/bcc/tools/argdist
    /usr/share/bcc/tools/bashreadline
    /usr/share/bcc/tools/biolatency
    ...
    /usr/share/bcc/tools/doc
    /usr/share/bcc/tools/doc/argdist_example.txt
    /usr/share/bcc/tools/doc/bashreadline_example.txt
    /usr/share/bcc/tools/doc/biolatency_example.txt
    /usr/share/bcc/tools/doc/biosnoop_example.txt
    ...
    /usr/share/man/man8/bcc-argdist.8.gz
    /usr/share/man/man8/bcc-bashreadline.8.gz
    /usr/share/man/man8/bcc-biolatency.8.gz
    /usr/share/man/man8/bcc-biosnoop.8.gz
    /usr/share/man/man8/bcc-biotop.8.gz

### BCC收集的eBPF应用 ###

BCC的命令较多，单开一篇笔记，这篇到此为止。

## 参考 ##

1.  [张亦鸣: eBPF 简史][eBPF 4]
2.  [BCC - Tools for BPF-based Linux IO analysis, networking, monitoring, and more][BCC 1]
3.  [Kernel Documentation：BPF Documentation][Kernel Documentation_BPF Documentation]
4.  [Linux Socket Filtering aka Berkeley Packet Filter (BPF)][Linux Socket Filtering aka Berkeley Packet Filter _BPF]
5.  [The BSD Packet Filter: A New Architecture for User-level Packet Capture][The BSD Packet Filter_ A New Architecture for User-level Packet Capture]
6.  [A thorough introduction to eBPF][LWN.net_ A thorough introduction to eBPF]
7.  [XDP：eXpress Data Path][XDP]
8.  [How to Upgrade Kernel on CentOS 7][]
9.  [Welcome to the ELRepo Project][]
10. [CentOS7/6内核升级的简单方法：借助ELRepo，用yum命令更新内核][CentOS7_6_ELRepo_yum]
11. [LWN.net: An introduction to the BPF Compiler Collection][LWN.net_ An introduction to the BPF Compiler Collection]
12. [samples/bpf][samples_bpf]
13. [LWN.net: Some advanced BCC topics][LWN.net_ Some advanced BCC topics]
14. [LWN.net: Using user-space tracepoints with BPF][LWN.net_ Using user-space tracepoints with BPF]
15. [Installing BCC][]
16. [bcc Tutorial][]
17. [bcc Python Developer Tutorial][]
18. [BPF: the universal in-kernel virtual machine][BPF_ the universal in-kernel virtual machine]
19. [使用XDP(eXpress Data Path)防御DDoS攻击][XDP_eXpress Data Path_DDoS]

[https_www.lijiaocn.com_E6_8A_80_E5_B7_A7_2019_02_25_ebpf-introduction-1.html]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html
[Link 1]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html#%E7%9B%AE%E5%BD%95
[Link 2]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html#%E8%AF%B4%E6%98%8E
[BPF]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html#bpf
[eBPF]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html#ebpf%E5%B8%A6%E6%9D%A5%E7%9A%84%E6%96%B0%E5%8F%98%E5%8C%96
[eBPF 1]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html#ebpf%E4%BD%BF%E7%94%A8
[Link 3]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html#%E5%8D%87%E7%BA%A7%E5%86%85%E6%A0%B8
[eBPF 2]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html#ebpf%E4%BB%A3%E7%A0%81%E7%A4%BA%E4%BE%8B
[eBPF 3]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html#ebpf%E4%BB%A3%E7%A0%81%E7%BC%96%E8%AF%91%E8%A3%85%E8%BD%BD
[BCC_eBPF]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html#%E4%BD%BF%E7%94%A8bcc%E7%AE%80%E5%8C%96ebpf%E5%BA%94%E7%94%A8%E5%BC%80%E5%8F%91%E8%BF%87%E7%A8%8B
[BCC]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html#bcc%E5%AE%89%E8%A3%85
[BCC_eBPF 1]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html#bcc%E6%94%B6%E9%9B%86%E7%9A%84ebpf%E5%BA%94%E7%94%A8
[Link 4]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/ebpf-introduction-1.html#%E5%8F%82%E8%80%83
[BCC 1]: https://github.com/iovisor/bcc
[eBPF 4]: https://www.ibm.com/developerworks/cn/linux/l-lo-eBPF-history/index.html
[BPF_ the universal in-kernel virtual machine]: https://lwn.net/Articles/599755/
[The BSD Packet Filter_ A New Architecture for User-level Packet Capture]: https://www.tcpdump.org/papers/bpf-usenix93.pdf
[Kernel Documentation_BPF Documentation]: https://www.kernel.org/doc/Documentation/bpf/
[Linux Socket Filtering aka Berkeley Packet Filter _BPF]: https://www.kernel.org/doc/Documentation/networking/filter.txt
[XDP]: https://www.iovisor.org/technology/xdp
[XDP_eXpress Data Path_DDoS]: https://blog.csdn.net/dog250/article/details/77993218
[seccomp]: https://lwn.net/Articles/656307/
[Userland Statically Defined Tracepoints]: https://www.memsql.com/blog/bpf-linux-performance/
[LWN.net_ A thorough introduction to eBPF]: https://lwn.net/Articles/740157/
[LWN.net_ An introduction to the BPF Compiler Collection]: https://lwn.net/Articles/742082/
[LWN.net_ Some advanced BCC topics]: https://lwn.net/Articles/747640/
[LWN.net_ Using user-space tracepoints with BPF]: https://lwn.net/Articles/753601/
[CentOS7_6_ELRepo_yum]: https://www.lijiaocn.com/%E6%8A%80%E5%B7%A7/2019/02/25/centos-kernel-upgrade.html
[samples_bpf]: https://elixir.bootlin.com/linux/v4.14.2/source/samples/bpf
[bcc Tutorial]: https://github.com/iovisor/bcc/blob/master/docs/tutorial.md
[bcc Python Developer Tutorial]: https://github.com/iovisor/bcc/blob/master/docs/tutorial_bcc_python_developer.md
[How to Upgrade Kernel on CentOS 7]: https://www.howtoforge.com/tutorial/how-to-upgrade-kernel-in-centos-7-server/
[Welcome to the ELRepo Project]: https://elrepo.org/tiki/tiki-index.php
[Installing BCC]: https://github.com/iovisor/bcc/blob/master/INSTALL.md