Re: [PATCH] rust: add basic ELF sections parser

["Alexandre Courbot" <acourbot@nvidia.com>]

On Fri May 16, 2025 at 10:15 PM JST, Greg KH wrote:
> On Thu, May 15, 2025 at 12:17:00PM -0700, John Hubbard wrote:
>> On 5/15/25 7:30 AM, Timur Tabi wrote:
>> > On Thu, May 15, 2025 at 6:43 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>> >>> Or if ELF is the problem, I don't mind introducing a WAD loader. ;)
>> >>
>> >> The "problem" I'm not understanding is why does the kernel have to do
>> >> any of this parsing at all?
>> > 
>> > Nova will need to parse ELF headers in order to properly load and boot
>> > Nvidia firmware images.  Nouveau does this already:
>> > 
>> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c#n2931
>> 
>> Hi Greg!
>> 
>> Nouveau influenced us heavily here, because having firmware that we
>> can post once, and use everywhere (Nouveau and Nova), is very attractive.
>> 
>> Alex and Timur discuss other details that explain why the standard 
>> user-space approach is less simple and clean than it might appear at
>> first glance, but I wanted to emphasize that the firmware re-use point
>> a little bit, too.
>> 
>> Oh, and also: the ELF images are going to remain extremely simple,
>> because there is nothing now (nor can I see anything in the future)
>> that would drive anyone to do complicated things. For example, if
>> there is some exotic new thing in the future, it could be put into
>> its own firmware image if necessary--because we understand that
>> this parser here is intended to be a simple subset of ELF, and
>> left alone really.
>
> Ok, then why not just bury this down in the driver that is going to
> actually use it?  This patch series was adding it to ALL kernels, if you
> need/want it or not, and as such would be seen as a generic way to
> handle all ELF images.  But as that's not the case here, just copy what
> you did in the existing C driver and make it private to your code, so
> that no one else has to worry about accidentally thinking it would also
> work for their code :)

Keeping this local to nova-core is perfectly fine if you think this is
more acceptable. AFAIK there are no other users for it at the moment.

> And I still think that having the kernel do this is a mistake, firmware
> should always just be a "pass through" otherwise you open yourself up to
> all sorts of complexity and vulnerabilities in the kernel, both of which
> is generally not a good idea.

I agree on principle, but I cannot think of a way to avoid doing this in
the kernel without making things overly complex. We're happy to consider
alternatives though, if they exist.