Two research passes confirmed the identity record itself (seed/pubkey/
cert) is already unreachable from any FORTH primitive -- only C-level
read_devblock/write_devblock touch it. But a device's ordinary user block
content CAN be copied between two attached devices today, using only
stock, unpinned words: <src> BLOCK <dst> BUFFER 1024 MOVE UPDATE
SAVE-BUFFERS, or the dedicated RELOCATE-BLOCK word (whose own doc comment
already admits "performs no policy validation of its own"). Checked
whether the existing per-block owner_fp/BLK-ACL-ALLOW@ metadata already
solves this -- it doesn't: owner_fp encodes who (a VM identity pubkey),
never where (physical device), and blk_get_buffer()/blk_update() never
consult acl_allow/acl_ttl at all -- those fields are completely inert.
Small, targeted fix, no rearchitecture:
- blk_subsys_relocate_block() (block_subsystem.c): same-device check.
Its own documented purpose is wear-leveling (relocate on the SAME
device) -- never stated as cross-device, and nothing enforced that
until now.
- New public blk_lbn_device_handle() (block_subsystem.c/.h): the missing
LBN-to-device direction (blk_get_device_range() already goes the other
way). Opaque, stable, == comparable.
- MOVE (memory_words.c) and CMOVE/CMOVE> (string_words.c): refuse when
both addresses are block-window addresses backed by two different
devices -- the exact shape of the composed attack. A copy where either
end is ordinary VM memory (the overwhelming common case: staging text
from PAD, editing a block in place) is untouched.
- blk_vm_check_epoch()/blk_vm_slot_for_addr() exposed (block_words.h) so
the two new call sites share the same window-slot invalidation contract
rather than a second, divergent copy of it.
Verified live on all three architectures, not just boot-clean: same-
device MOVE/RELOCATE-BLOCK still succeed exactly as before; cross-device
MOVE/CMOVE/RELOCATE-BLOCK all refused. Zero UNKNOWN WORD, identical
dict_hash across all three (this change adds no FORTH-visible word, only
internal refusal conditions, as predicted).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
