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The Verifier: Why eBPF Doesn't Crash the Kernel

Article 1 said the eBPF virtual machine design lets the verifier prove safety. This article watches it for real: we compile an XDP program that reads the first byte of a packet but forgets the bounds check, load it — the verifier rejects it with a log naming the exact register and reason. Add one data_end check and it goes through. The verifier is a safety prover at load time, tracking each register's state across every branch — letting eBPF load foreign code into the kernel safely.