Introduction to Linux eBPF

Understanding eBPF Architecture

eBPF stands for Extended Berkeley Packet Filter, and it's a powerful technology that allows developers to run sandboxed programs in the Linux kernel without changing kernel source code or loading kernel modules. At its core, eBPF consists of a virtual machine that executes bytecode in the context of various kernel events, enabling a myriad of functionalities—from performance monitoring to security enhancements.

Key Components of eBPF

To grasp eBPF architecture, let’s break it down into its essential components:

eBPF Programs: These are small, efficient pieces of code compiled into bytecode that run inside the kernel. eBPF programs can be attached to various hooks or events that the kernel exposes.
Maps: Maps are used to store state between eBPF program invocations. They provide a way for programs to share data with one another or with user space applications, allowing for more dynamic interactions and functionality.
Verification: Before eBPF bytecode is executed, it’s checked by the eBPF verifier. This step ensures that the program is safe to run—no infinite loops or illegal memory accesses are permitted. This step is crucial for maintaining system stability and security.
Hook Points: These are pre-defined locations in the kernel where eBPF programs can be attached, such as network events, trace points, or security hooks. The flexibility in hook points allows eBPF to be versatile in its applications.

Use Cases of eBPF

The power of eBPF lies in its versatility. Below are some of the most common and impactful use cases of eBPF:

1. Network Performance Monitoring

eBPF provides advanced networking capabilities, enabling deep insights into network performance. Applications can leverage eBPF to collect metrics such as packet counts, latencies, and error rates. For instance, tools such as bpftrace and xdp utilize eBPF for high-performance packet filtering and network diagnostics, allowing operators to detect issues and improve network latency without impacting overall performance.

2. Security Enhancements

With eBPF, security monitoring becomes more granular and effective. Programs can be used to monitor system calls, detect suspicious behavior, and enforce security policies dynamically. Projects like Cilium leverage eBPF for enforcing network policies and securing workloads, proving eBPF’s capability as a robust security tool.

3. Performance Profiling and Debugging

eBPF can capture detailed metrics about system and application performance. With tools like perf, developers can attach eBPF programs to track CPU cycles, context switches, and other critical metrics. This insight enables developers to diagnose performance bottlenecks and optimize the code effectively.

4. Application Observability

One of the most exciting aspects of eBPF is its contribution to application observability. Tools such as tracee and strace use eBPF to provide real-time insights into application behaviors and dependencies. This helps maintain healthy microservices architectures, where observability is paramount.

5. Custom Protocol Support

With eBPF, it is possible to receive and process custom networking protocols efficiently. Developers can write eBPF code to understand and manipulate packets at the kernel level. This capability allows custom networking solutions and enhancements without the need for heavy modifications to existing kernel code.

Writing Your First eBPF Program

Now that you understand the architecture and use cases of eBPF, let’s dive into how to write your first eBPF program. Below is a simple example that counts the number of packets received on a specific network interface.

Prerequisites

Make sure you have the following prerequisites for this example:

A Linux kernel version that supports eBPF (4.1 and above).
The clang compiler and llvm for compiling eBPF code.
The libbpf library installed for easier handling of eBPF functionalities.

Step 1: Write eBPF Code

Here’s a simple eBPF program in C that counts packets received on the eth0 interface:

#include <linux/bpf.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#define SEC(NAME) __attribute__((section(NAME), used))

SEC("filter/count_packets")
int count_packets(struct __sk_buff *skb) {
    __u32 *packet_count;
    packet_count = bpf_map_lookup_elem(&packet_map, &key);
    if (packet_count) {
        (*packet_count)++;
    }
    return XDP_PASS; // Pass the packet to the kernel
}

Step 2: Compile the eBPF Program

You can compile the above code using clang with -target bpf option:

clang -O2 -target bpf -c count_packets.c -o count_packets.o

Step 3: Load and Attach the eBPF Program

You would typically use a user-space program to load and attach the eBPF to the desired interface. Below is a sample command using bpftool:

bpftool prog load count_packets.o /sys/fs/bpf/count_packets
bpftool net attach xdp id <PROGRAM_ID> dev eth0

Step 4: View the Results

Finally, you can retrieve and view the packet counts stored in the map with another bpftool command or by writing a small user-space program to reference the map.

Conclusion

eBPF represents a paradigm shift in Linux kernel programming, offering a modular and flexible way to extend kernel capabilities without compromising security or stability. Its application in various fields—from networking to observability and security—shows how eBPF can empower developers to create powerful tools that operate close to the metal.

As the ecosystem around eBPF continues to grow, with numerous tools and libraries emerging, diving deeper into eBPF is not just recommended; it’s exciting! Whether you focus on performance tuning, security measures, or custom networking solutions, eBPF provides an engaging and rewarding development experience that aligns with modern computing needs.

The world of eBPF is vast and promising, so stay tuned for more in-depth articles and practical examples in our series on this groundbreaking technology!

Networking & Infrastructure - Linux eBPF