[step0] control port access, IOPL=0 -> SIGSEGV (expect SIGSEGV/#GP)
[step1] open(/dev/io) ok, IOPL now = 3 (expect 3)
[step2] port access with fd: OK (expect OK)
[step3] parent closed fd (last close), parent IOPL=0 (expect 0 — clr hit closer)
[step4] child: all /dev/io fds closed, IOPL=3 (contract says 0)
[step4] child: port access after last close: OK — GRANT OUTLIVED THE FD
[step5] child: uid=65534 IOPL=3 port access: OK — GRANT SURVIVED PRIVILEGE DROP
[done ] child exit status 0
EXIT=0