eBPF, or extended Berkeley Packet Filter, is a technology that allows small, sandboxed programs or scripts to run in the kernel space of a Linux system without having to change the kernel’s source code or load Linux kernel modules.
A Linux system has two spaces: the kernel and the user space. The kernel represents the operating system’s core and is the only part with unlimited access to the hardware.
Applications reside in the user space, and when they need higher permissions, they send a request to the kernel. For applications that require more flexibility, such as direct hardware access, the kernel can be extended via what is known as the “Linux kernel modules” approach. This approach extends the kernel’s default functionality, allowing applications deeper access to the underlying components. However, this approach also introduces security risks, making eBPF an attractive alternative.
Problem it addresses
Typically, applications run in the user space, and if the application requires some privileges from the kernel (e.g., to access some hardware),
it requests it from the kernel via a so-called “system call.”
In most cases, this approach works just fine. However, there are instances where developers require more flexibility for low-level system access. Observability, security, and networking features are good examples. To achieve that, we can use Linux kernel modules, extending the kernel base without modifying the kernel source code. While there are benefits to using Linux kernel modules, it also introduces security risks. Because they operate within the kernel space, Linux kernel modules can crash the kernel, and when the kernel crashes, so does the entire machine. Additionally, kernel modules have elevated privileges and direct access to system resources. And if not properly secured, attackers can exploit these.
How it helps
eBPF provides a more controlled and contained environment for executing user-defined programs than Linux Kernel modules. It runs in a sandboxed environment within the kernel, providing isolation and mitigating risk. If a vulnerability or flaw is exploited in an eBPF program, its impact is generally limited to the sandboxed environment. Moreover, before an eBPF program can start running in the kernel, it has to pass some verifications. The verifier component checks the eBPF program for potential safety violations, such as out-of-bounds memory access, infinite loops, and unauthorized kernel functions. This way, it ensures the program won’t enter an infinite loop and cause a kernel crash. These safety controls make eBPF a more secure option to run applications in the Linux kernel than the Linux kernel modules.
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