linux-kernel - Re: [PATCH] rust: add basic ELF sections parser

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Message-Id: <D9XMAV4ERYK7.39TLQBLYTX3TU@nvidia.com>
Date: Fri, 16 May 2025 22:26:10 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Greg KH" <gregkh@...uxfoundation.org>, "John Hubbard"
 <jhubbard@...dia.com>
Cc: "Timur Tabi" <timur@...nel.org>, "Miguel Ojeda" <ojeda@...nel.org>,
 "Alex Gaynor" <alex.gaynor@...il.com>, "Boqun Feng" <boqun.feng@...il.com>,
 "Gary Guo" <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, "Benno Lossin" <benno.lossin@...ton.me>,
 "Andreas Hindborg" <a.hindborg@...nel.org>, "Alice Ryhl"
 <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>, "Danilo
 Krummrich" <dakr@...nel.org>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH] rust: add basic ELF sections parser

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@...uxfoundation.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.