linux-kernel - Re: [PATCH v2 2/8] gpu: nova-core: firmware: add support for common firmware header

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Message-ID: <2532f8a1-83ba-4f72-aae7-9d810eda417a@nvidia.com>
Date: Wed, 27 Aug 2025 14:50:36 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Alexandre Courbot <acourbot@...dia.com>, 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 <lossin@...nel.org>,
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>
Cc: Alistair Popple <apopple@...dia.com>,
 Joel Fernandes <joelagnelf@...dia.com>, Timur Tabi <ttabi@...dia.com>,
 rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
 nouveau@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2 2/8] gpu: nova-core: firmware: add support for common
 firmware header

On 8/27/25 1:47 AM, Alexandre Courbot wrote:
> On Wed Aug 27, 2025 at 10:34 AM JST, John Hubbard wrote:
> <snip>
>>> +    /// Returns the data payload of the firmware, or `None` if the data range is out of bounds of
>>> +    /// the firmware image.
>>> +    fn data(&self) -> Option<&[u8]> {
>>> +        let fw_start = self.hdr.data_offset as usize;
>>> +        let fw_size = self.hdr.data_size as usize;
>>> +
>>> +        self.fw.get(fw_start..fw_start + fw_size)
>>
>> This worries me a bit, because we never checked that these bounds
>> are reasonable: within the range of the firmware, and not overflowing
>> (.checked_add() for example), that sort of thing.
>>
>> Thoughts?
> 
> `get` returns `None` if the requested slice is out of bounds, so there
> should be no risk of panicking here.

I was wondering about the bounds themselves, though. Couldn't they
be wrong? (Do we care?)

> 
> However, `fw_start + fw_size` can panic in debug configuration if it
> overflows. In a release build I believe it will just happily wrap, and
> `get` should consequently return `None` at the invalid range... Although
> we can also get unlucky and produce a valid, yet incorrect, one.
> 
> This is actually something I've been thinking about while writing this
> series and could not really decide upon: how to deal with operands and
> functions in Rust that can potentially panic. Using `checked` operands
> everywhere is a bit tedious, and even with great care there is no way to
> guarantee that no panic occurs in a given function.

Yes, .checked_add() all over the place is just awful, would like to 
avoid that for sure.

> 
> Panics are a big no-no in the kernel, yet I don't feel like we have the
> proper tools to ensure they do not happen.
> 
> User-space has some crates like `no_panic`, but even these feel more
> like hacks than anything else. Something at the compiler level would be
> nice.
> 
> Maybe that would be a good discussion topic for the Plumber
> Microconference?

Yes. And maybe even for Kangrejos.

thanks,
-- 
John Hubbard