Re: Using Rust on non-Rust side of kernel

[Jarkko Sakkinen <jarkko@kernel.org>]

Hi,

Would it be possible to response in plain text?

BR, Jarkko

On Sat, Aug 23, 2025 at 11:38:00AM -0300, Daniel Almeida wrote:
> Hi Jarkko,
> 
> I must admit that I had a hard time understanding what you’re trying to say.
> 
> 
>     On 23 Aug 2025, at 09:22, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> 
> 
>     On Sat, Aug 23, 2025 at 03:12:48PM +0300, Jarkko Sakkinen wrote:
> 
>         Hi
> 
>        
> 
>         As of today can we possibly do this:
> 
>        
> 
>         1. drivers/char/tpm (C code)
> 
>         2. drivers/char/tpm/protocol (imported tpm2_protocol)
> 
>        
> 
> 
> What do you mean?
> 
> 
>         ?
> 
>        
> 
>         And then build FFI from C to Rust for building commands that we need
> 
>         today etc.
> 
>        
> 
>         There's one particular challenge where this could help: early boot code
> 
>         for D-RTM (i.e., Trenchboot) as given my crate is just a thing in stack
> 
>         with no deps, it could be linked also to that payload.
> 
>        
> 
>         This would be much better integration step for TPM2 than having a
> 
>         separate driver on Rust side. We could start with tpm2-cmd1/cmd2, then
> 
>         move on to tpm2-space.c i.e. get all structural processing inside Rust.
> 
> 
> Can you expand on what these cmds are?
> 
> 
>        
> 
>         tpm2_protocol is light on definitions and should not need any kernel
> 
>         specific Rust shenanigans.
> 
> 
> You mean the Rust abstractions?
> 
> 
>        
> 
>         Consider it as value like integer but just a bit more complex internaal
> 
>         represention but in the end it is just a value on stack.
> 
> 
> Not sure what you mean here either.
> 
> 
>        
> 
>         My goal with tpm2_protocol is to have ACPICA alike model of imports as
> 
>         the crate is driven by TCG spec updates and it is very likely to be
> 
>         also used by TPM-RS (also via import style process).
> 
>    
>     The source code since 0.10.0 version has been relocated here:
>    
>     https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/tpm2-protocol.git
>    
>     The representation of commands and responses defined is pretty well
>     high-lighted by
>    
>     https://bsky.app/profile/jarkk0.bsky.social/post/3lx2n2uvxos2h
>    
>     I'm also working on a test that measures the estimated compile time
>     size and realized run-time size (suggested by Philip Tricca) so that
>     we know where we are at on stack usage.
>    
>     I've started to optimize it after development phase with some
>     low-hanging fruit cut already in 0.10.0 but this work is barely
>     starting [1].
>    
>     There's also a kselftest compatible test that can be run with
>     "make test" in the repo using only rustc (build + run circa
>     2 seconds on my laptop).
>    
>     [1] https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/
>     tpm2-protocol.git/commit/?id=cd6641bf9e8c8fde8726bece9eb6cdc630d893c2
>    
>     BR, Jarkko
> 
> 
> 
> 
> My somewhat limited understanding here is that you’re trying to implement Rust
> code that can be called from the rest of the kernel, but that otherwise doesn’t
> depend on it? 
> 
> 
> If so, I did try something similar [0]. Perhaps this is useful to you and is
> somewhat applicable to your use case as well?
> 
> [0]: https://lwn.net/Articles/970565/
> 
>