Tock Core Notes 2021-10-08

Attendees

Brad: Hard/impossible to get debug printing traits for everything, but does work for printing the memory map. PR is open and updated.
Phil: Using autogenerated registers for OpenTitan. Plan to keep them separate files for now (since they change often). Eventually merge them into the driver file once stabilized.
- No longer just constants, actually generating the register macro now.
Jett: Going to update the time HIL to remove the 'a lifetime.

https://github.com/tock/tock/blob/appid/doc/reference/trd-appid.md
End of section 4.
Challenge: generate compiled binary, then want to include TBF header. Integrity protection needs to cover code binary and headers, but not the credentials header.
Header has length. Need to pick some length, then compute header value and then insert in TBF header.
Should an app be signable serially? Or do all signatures have to happen at once?
Do signatures stack? Or does the second signature sign the previous signature?
- Idea: signature 2 signs over previous signature. Benefit would be could add an arbitrary number of signatures.
Verifier decides how to handle if there are multiple signatures.
Examples would help with why multiple signatures.
- Do Tock users want to do this?
- Work on use cases.
Idea: put signature/credentials in a "container" separate from TBF.
Idea: put signatures at the end, perhaps as some sort of list.
Various technical implementations proposed and discussed.
note: ARM MPU requires power of 2, appending to the binary would today double the length.
Signatures could be large (kilobytes) so reserving space could add a fair bit of speculative overhead.

Incorporated comments.
- "Word" -> "Character"
API change
- abort() result. https://github.com/tock/tock/blob/d834efc6a880a2561019b86162e9e5b08dc22f10/doc/reference/trd-uart.md#3-transmit-and-transmitclient
- Used to be: Ok() gets callback, Err() does not.
- Now has AbortResult, whether abort worked, and whether there will be a callback.
  - Idea: use three different fields in enum, no bool. Can add helper functions.