A protocol is reached by name now, not by a compile-time integer. Init is
PID 1 and already knows which binary it started, so init serves /protocol
as a vfs backend: bind claims a contract with the provider's endpoint
attached, open answers with that endpoint as the reply's capability, and
readdir lists what is bound with the task and binary behind it. The kernel
reserves the prefix — nothing may mount over it, under it, or unmount it —
and ServiceId, ipc_register and ipc_lookup are gone, their syscall numbers
left vacant.
A bind is authorized by who the caller *is*: the kernel-stamped binary
together with the supervising task's identity, matched against
/system/configuration/protocol.csv. Identity, not spelling — spawn is
ungated, so an attacker can run any bundled binary, and a name-only rule
would have let it launder grants through an init of its own making. A name
a live process holds is refused to everyone else; a dead one's is released.
Three review rounds against a hostile ring-3 process found what 108 green
tests could not, because the suite contains no attacker. Publishing init's
supervision endpoint as the registry put PID 1's mailbox in every process's
hands, where two forged bytes reached the shutdown path: privileged traffic
is now believed only from the task that holds the contract it speaks for.
A capability arriving on a request outlived every path that ignored it,
one handle per call until the table was full — in init, and in the harness
ten services share — so the arriving capability is owned by the turn and
released unless a handler says otherwise. And the kernel let anyone holding
an endpoint handle aim signals, timers, exit notices and interrupts at it:
binding now requires having created it.
Suite 108/108. The new protocol-registry case asserts eleven properties,
each one an attack that must fail.
A new user-memory module owns every kernel touch of a user buffer:
copyFromUser, the new copyToUser, and the resolve behind both. The walk
accumulates the U/S and writable bits down all four levels with the MMU's
own AND rule — folding a 2 MiB leaf in before it resolves and refusing a
1 GiB leaf outright — so a copy honours what ring 3 itself would be
allowed, closing the presence-only trust model the IPC layer carried since
bring-up. It then confirms the frame is physmap-backed, because that is how
the copy reaches it: an mmio_map'd BAR passes the permission walk and would
otherwise fault ring 0 on an alias the physmap never mapped, on the IPC path
as much as the new one.
The nine stragglers that dereferenced user pointers raw now route through
it, so a bad pointer returns -EFAULT where it used to fault the kernel.
The write direction restructures its callees around kernel bounce buffers:
scheduler and devices-broker enumerate from a slot cursor (a task exiting
between chunks can neither duplicate nor lose an entry), klog_read drains
the ring in chunks, and fs_node stages headers and names contiguously.
fs_resolve copies out before installing the endpoint handle, so a faulting
copy cannot strand a capability; its out-capacity bound no longer adds an
unbounded ring-3 length to the base, which wrapped and trapped the kernel's
own overflow check. debug_write reads the caller's message once.
Suite 107/107 (new user-memory case: seven bad pointers refused, each
paired with a sound call that must still succeed).
/etc/init.csv and /etc/devices.csv become /system/configuration/*.csv (the
repo's etc/ moves to system/configuration/, mirroring the runtime tree),
/var/log becomes /system/logs, and /mnt/usb becomes /volumes/usb. The
kernel VFS gains a carve-out so FAT may serve exactly /system/configuration
and /system/logs beneath the initrd-backed /system while /system and /test
themselves stay unshadowable; FAT's single /var mount splits into those two
rewritten mounts. The kvfs readdir check learns /system's third child and
the ramdisk spawn sweep skips the configuration tree.
Suite 106/106.
The 11 QEMU-suite fixtures lived mixed into system/services/ with their
binaries bundled at /system/tests/<name>. Now the repo path is the boot
path, like every real service: test/system/services/<name>. fat-test
moves out of the fat server's directory into its own; display-demo
stays a boot service.
- kernel VFS: setInitialRamdisk derives one read-only initrd mount per
top-level tree named by the ramdisk entry paths (/system, /test),
registers ancestors generically with self-parented roots, and refuses
backend shadowing of any initrd tree
- EFI loader: the fallback walk also enumerates \test (optional — a
volume without fixtures still boots); manifest and capsule unchanged
- path literals: vfs-test self-open + create probe, process-test
process_enumerate matches, the args-echo argv[0] expectation; the
kvfs case now covers the /test root end to end
- docs: DFHS /test rows, tree diagrams, loader prose, and the location
convention gain the third home; fixed the input-source link
100/100 QEMU cases pass.
system/kernel/vfs.zig is the resolve+redirect router: fs_resolve (#46)
walks the kernel mount table; a path under the kernel-backed /system
mount (the initrd, seeded by setInitialRamdisk with a derived directory
table) yields a permanent stateless node token served by fs_node (#47)
— read/status/readdir with copy-out, initrd reads lock-free — while a
path under a userspace mount yields the backend's endpoint (installed
in the caller's table, DEDUPLICATED so 16 slots can't be exhausted by
repeated resolves) plus the rewritten mount-relative path; the caller
then speaks the unchanged vfs-protocol rendezvous directly. The kernel
never blocks on a userspace filesystem, holds no open-file state, and
refuses create-intent on the immutable /system.
fs_mount (#48) is the syscall form of the old router's op-6 cap-pass
(possession of the backend handle is the capability; an optional
rewrite prefix maps the mount into the backend's namespace — how /var
will reach the flash volume); fs_unmount (#49) removes one. A dead
backend's mount clears lazily on resolve.
Dormant this milestone: the userspace vfs still serves runtime.fs
unchanged; the kvfs QEMU case covers the kernel side (resolution, ELF
magic read-through, /system listing, read-only + unknown refusals)
until the M-G cutover exercises the syscalls end-to-end.
Daniel Samson