#!/bin/sh
# DF-4637 trigger — DOCUMENTED ONLY, NOT EXECUTED (no ppbus hardware on audit guest).
#
# Preconditions (hardware): parallel port (ppc(4)) + Iomega VP0 ZIP (vpo(4) kldload'ed,
# drive enumerated as /dev/daN) where the attached device is a *malicious emulator*
# that completes select/connect but never asserts nBUSY during cmd/data/status waits.
#
# Run as any user with read access to the da device (operator group on default devfs
# rules), or as root:
#
#   dd if=/dev/da1 of=/dev/null bs=512 count=1
#
# Expected on a vulnerable system: the issuing CPU stalls inside crit_enter() for the
# duration of the microseq spins (up to ~13M status-register polls per command —
# seconds per I/O, interrupts deferred, thread unkillable). Repeat per I/O.
#
# Guest check performed 2026-09-22 (env.txt): no ppc/ppbus/lpt/parallel in dmesg or
# pciconf; /boot/kernel/vpo.ko exists but cannot attach -> not runnable here.
exit 0