BPF, or the Berkeley Packet Filter, is a Linux kernel mechanism for running small, restricted programs inside the kernel. It is used for packet filtering, tracing, monitoring, and sandboxing. Modern Linux often uses eBPF, a more flexible version, and many deployments rely on JIT compilation so BPF bytecode is translated into native CPU instructions for speed.
In security, BPF matters because it sits close to sensitive kernel paths and can influence what data is inspected, allowed, or blocked. Its JIT layer also makes it relevant to microarchitectural attacks: if compiled code is reused or replaced, stale branch-prediction state can sometimes be abused to steer speculative execution, which is why BPF hardening and Spectre-v2 mitigations are important. Defenders use BPF for visibility and enforcement, while attackers may target it as an execution surface or as part of a side-channel chain.