Berkeley Packet Filter

Abstract: Extended Berkeley Packet Filter (eBPF) is an instruction set and an execution environment inside the Linux kernel. It enables modification, interaction, and kernel programmability at runtime. eBPF can be used to program the eXpress Data Path (XDP), a kernel network layer that processes packets closer to the NIC for fast packet processing. Developers can write programs in C or P4 languages and then compile to eBPF instructions, which can be processed by the kernel or by programmable devices (e.g., SmartNICs). Since its introduction in 2014, eBPF has been rapidly adopted by major companies such as Facebook, Cloudflare, and Netronome. Use cases include network monitoring, network traffic manipulation, load balancing, and system profiling. This work aims to present eBPF to an inexpert audience, covering the main theoretical and fundamental aspects of eBPF and XDP, as well as introducing the reader to simple examples to give insight into the general operation and use of both technologies.

Abstract: The extended Berkeley Packet Filter (eBPF) is a recent technology available in the Linux kernel that enables flexible data processing. However, so far the eBPF was mainly used for monitoring tasks such as memory, CPU, page faults, traffic, and more, with a few examples of traditional network services, e.g., that modify the data in transit. In fact, the creation of complex network functions that go beyond simple proof-of-concept data plane applications has proven to be challenging due to the several limitations of this technology, but at the same time very promising due to some characteristics (e.g., dynamic recompilation of the source code) that are not available elsewhere. Based on our experience, this paper presents the most promising characteristics of this technology and the main encountered limitations, and we envision some solutions that can mitigate the latter. We also summarize the most important lessons learned while exploiting eBPF to create complex network functions and, finally, we provide a quantitative characterization of the most significant aspects of this technology.

Abstract: Extended Berkeley Packet Filter (eBPF) is a Linux subsystem that allows safely executing untrusted user-defined extensions inside the kernel. It relies on static analysis to protect the kernel against buggy and malicious extensions. As the eBPF ecosystem evolves to support more complex and diverse extensions, the limitations of its current verifier, including high rate of false positives, poor scalability, and lack of support for loops, have become a major barrier for developers. We design a static analyzer for eBPF within the framework of abstract interpretation. Our choice of abstraction is based on common patterns found in many eBPF programs. We observed that eBPF programs manipulate memory in a rather disciplined way which permits analyzing them successfully with a scalable mixture of very-precise abstraction of certain bounded regions with coarser abstractions of other parts of the memory. We use the Zone domain, a simple domain that tracks differences between pairs of registers and offsets, to achieve precise and scalable analysis. We demonstrate that this abstraction is as precise in practice as more costly abstract domains like Octagon and Polyhedra. Furthermore, our evaluation, based on hundreds of real-world eBPF programs, shows that the new tool generates no more false alarms than the existing Linux verifier, while it supports a wider class of programs (including programs with loops) and has better asymptotic complexity.

Abstract: Firewall capabilities of operating systems are traditionally provided by inflexible filter routines or hooks in the kernel. These require privileged access to be configured and are not easily extensible for custom low-level actions. Since Linux 3.0, the Berkeley Packet Filter (BPF) allows user-written extensions in the kernel processing path. The successor, extended BPF (eBPF), improves flexibility and is realized via a virtual machine featuring both a just-in-time (JIT) compiler and an interpreter running in the kernel. It executes custom eBPF programs supplied by the user, effectively moving kernel functionality into user space. We present two case studies on the usage of Linux eBPF. First, we analyze the performance of the eXpress Data Path (XDP). XDP uses eBPF to process ingress traffic before the allocation of kernel data structures which comes along with performance benefits. In the second case study, eBPF is used to install application-specific packet filtering configurations acting on the socket level. Our case studies focus on performance aspects and discuss benefits and drawbacks.