Six steps an agent can execute: reclamation, the bounds build check, and
the four user-space USB/xHCI bounds where the hardware already reports the
number we guessed.
Deliberately excluded: the authorisation gate and moving the device
inventory to the manager. Both decide whether the OS is secure and both are
a direction rather than a specification — what a device capability is, which
syscalls change, what replaces device_claim for its seven callers. They want
a design session, not an agent.
Three open questions are written down rather than guessed: device_enumerate
most likely narrows to the firmware-discovered roots rather than retiring
(the manager cannot ask itself for the PCI host bridge); a manager restart
has no re-enumerate handshake, so it comes back blind while its buses live;
and "add adversarial tests" is not executable until the attacks are named.
An AMD Ryzen booted to a working compositor with no USB and no storage,
and the log said only "register refused". A tree-wide audit of every
compile-time ceiling followed: 235 of them, 139 on quantities the machine
or a file decides rather than us, 5 documented anywhere, 171 silent when
reached. docs/fixed-bounds-audit.md has the inventory.
Errno attribution. The errno space was split between the kernel and the
envelope, free to drift; it is now one list in system/abi.zig, restated on
both sides, with a comptime check in library/device/driver where the two
halves are visible. device_register's six refusals and device_claim's three
are distinct codes, so a bus driver can say which rule stopped it, and
BadParent splits into NoSuchParent and NotYourParent. pci-bus reconciles
found against registered instead of counting refused functions as found.
Idempotency ordering. The child cap was checked before the identity match,
so a restarted bus was refused its own devices — the supervision restart the
system leans on ratcheted toward a degraded machine. A re-registration
consumes no slot and is now admitted first.
IOMMU fail-closed. confineDevice returned success for a device id past the
confinement table, leaving the device outside every domain while the caller
believed it confined — unreachable only while ids stop at 64, which both the
inventory move and a hardware-reported domain count would change. It refuses
now, and the coupling to the broker's device cap is a comptime assert rather
than a sentence in a comment.
PCI apertures. The bridge's MMIO apertures are derived from the holes in the
firmware memory map, and the derivation copied sub-4 GiB entries into a
fixed [64] array and skipped the rest. A skipped region is not merely lost:
the gap finder concludes it is free, so a real machine's 60-200 entry map
yields an aperture over live RAM, and containment then admits a child BAR
covering kernel memory. Rewritten to walk the map in place, with the hole
finder extracted as a pure function and driven by a synthetic 100-entry map
in a new test case. Both new tests were verified to fail on the old code.
parameters.zig gains the rationale it was missing and loses a stale sentence
pointing at the wrong file; vdso.md documents the errno space, including
EPEER, which had no written meaning anywhere.
docs/os-development/bounds.md is how a ceiling is declared from here.
docs/bounds-track-plan.md is the plan to remove the ones we invented.
Suite 114 -> 115.
Daniel Samson