Re: [PATCH v4 1/2] Import CBOR library

[Alexander Graf <graf@amazon.com>]

Hey Greg,

On 10.10.23 08:13, Greg Kroah-Hartman wrote:
> On Mon, Oct 09, 2023 at 09:20:52PM +0000, Alexander Graf wrote:
>> To fully support the Nitro Secure Module communication protocol, we need
>> to encode and decode CBOR binary data. Import an MIT licensed library
>> from https://github.com/libmcu/cbor (commit f3d1696f886) so that we can
>> easily consume CBOR data.
> What is "CBOR"?  I don't see a description of it here.


CBOR is the "Concise Binary Object Representation" 
(https://en.wikipedia.org/wiki/CBOR) binary format.


>
> And I guess you are going to keep this in sync with upstream?  Or do you
> really need the full library here (you #ifdef the float stuff out), does
> your module really need all of the functionality and complexity of this
> library, or can it use just a much smaller one instead?


CBOR knows a total of 9 data types:

   - Unsigned integers
   - Signed integers
   - Binary string
   - UTF-8 string
   - Arrays
   - Maps (like a python dictionary)
   - Semantic tag
   - Bools
   - Floats

Out of these, the NSM communication protocol uses all except Semantic 
tags and Floats. The CBOR library that this patch imports does not have 
special handling for Semantic tags, which leaves only floats which are 
already #ifdef'ed out. That means there is not much to trim.

What you see here is what's needed to parse CBOR in kernel - if that's 
what we want to do. I'm happy to rip it out again and make it a pure 
user space problem to do CBOR :).


>
>> On top of the upstream code base, I added kernel module as well as
>> kernel header path awareness and made checkpatch happy.
> If only the one module needs this, why not put it in the directory for
> the module itself, and then when/if anyone else needs it, it could be
> moved?


That sounds like a great idea! Let me do that :)


Alex





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