Local information disclosure via uncleared atomic fetch register

Information disclosure in the s390x BPF JIT in Linux allows local users to read stale register data through faulting arena atomics. bpf_jit_probe_atomic_pre() leaves probe->reg unset for fetch-style read-modify-write operations, so ex_handler_bpf() fails to clear the destination register after an unmapped arena-page fault. Exploitation requires local access to an s390x system and a BPF program that performs the faulting operation; the documented consequence is stale register disclosure rather than memory modification or service interruption.