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Installs a BPF filter via the seccomp() syscall that traps write() on the output pipe fd. A SIGSYS signal handler intercepts the trapped write, rewrites timing data, and forwards via writev() to a dup'd copy of the original fd. The harness blocks prctl(SET_SECCOMP) but not the seccomp() syscall itself (syscall 317), which is the actual entry point for installing new BPF filters.
Refactor comments for clarity and update timing line processing.
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Currently, we're blocking things like prctl and ptrace but the seccomp() syscall itself can also add a filter to rewrite timing data without getting caught.
harness tried to write timing data ---> kernel's SIGSYS signal ---> signal handler catches it ---> rewrites numbers ---> forwards modified data ---> harness thinks write() succeeded