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

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Message-Id: <DCD2VJ1WJW2O.VM7E4PD3DFYO@nvidia.com>
Date: Wed, 27 Aug 2025 17:47:23 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "John Hubbard" <jhubbard@...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 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.

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.

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?