My understanding of this isn't as good as it could be (I haven't read the spec for the eBPF instruction set in https://www.kernel.org/doc/Documentation/networki

My understanding of this isn't as good as it could be (I haven't read the spec for the eBPF instruction set in https://www.kernel.org/doc/Documentation/networking/filter.txt https://www.kernel.org/doc/Documentation/networking/filter.t... yet). But my understanding is that there's a "jump" instruction in the BPF instruction set and what the verifier does is ensures that all jumps go forwards and not backwards. This 2014 LWN article https://lwn.net/Articles/603983/ https://lwn.net/Articles/603983/ says that the verifier in the kernel is responsible for verifying there are no loops: > The verifier looks for a number of things. It tracks the state of every eBPF register and will not allow their values to be read if they have not been set. To the extent possible, the type of the value stored in each register is also tracked. Load and store instructions can only operate with registers containing the right type of data (a "context" pointer, for example), and all operations are bounds-checked. The verifier also disallows any program containing loops, thus ensuring that all programs will terminate.