An extended-capability walk (pci_types capabilities()) that follows a
chain running to/past the end of config space read at offset 4096,
which tripped the dword-offset assert in bus_addr_offset_in_dwords
("pcie offset larger than 4095") and aborted pcid with an Invalid
opcode fault / UNHANDLED EXCEPTION on boot — after switchroot to /usr,
so it blocked reaching login.
PCIe config space is exactly 4096 bytes (offsets 0..=4095). Fix at two
levels:
- ConfigRegionAccess::read/write (cfg_access/mod.rs): guard the single
access choke point — an out-of-range read returns the PCI "no
response" pattern (0xFFFFFFFF, which also terminates a capability
walk cleanly) and an out-of-range write is a no-op. This catches any
caller (capability walk, scheme reads, driver access).
- scheme.rs config read/write loop: clamp the loop bound with
saturating_add(...).min(4096) so a consumer requesting offset+len
past the boundary reads only the valid part instead of looping to
offset 4096.
Verified: boot no longer panics in pcid (progresses past the previous
crash point through switchroot and the /usr driver set).
Red Bear OS
9c571e2942