linux-kernel - Re: [PATCH v2 1/5] gpu: nova-core: use checked arithmetic in FWSEC firmware parsing

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Message-Id: <DG0607SU943F.1FDOPYPN38FCS@kernel.org>
Date: Wed, 28 Jan 2026 11:53:48 +0100
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Joel Fernandes" <joelagnelf@...dia.com>
Cc: <linux-kernel@...r.kernel.org>, "Paul Walmsley" <pjw@...nel.org>,
 "Palmer Dabbelt" <palmer@...belt.com>, "Albert Ou" <aou@...s.berkeley.edu>,
 "Alexandre Ghiti" <alex@...ti.fr>, "Miguel Ojeda" <ojeda@...nel.org>,
 "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>,
 "Alexandre Courbot" <acourbot@...dia.com>, "John Hubbard"
 <jhubbard@...dia.com>, "Alistair Popple" <apopple@...dia.com>, "Timur Tabi"
 <ttabi@...dia.com>, "Edwin Peer" <epeer@...dia.com>, "Zhi Wang"
 <zhiw@...dia.com>, "David Airlie" <airlied@...il.com>, "Simona Vetter"
 <simona@...ll.ch>, "Bjorn Helgaas" <bhelgaas@...gle.com>, "Alex Gaynor"
 <alex.gaynor@...il.com>, "Dirk Behme" <dirk.behme@...il.com>,
 <nouveau@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
 <rust-for-linux@...r.kernel.org>, <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH v2 1/5] gpu: nova-core: use checked arithmetic in FWSEC
 firmware parsing

On Mon Jan 26, 2026 at 9:23 PM CET, Joel Fernandes wrote:
> @@ -267,7 +264,12 @@ fn new_fwsec(dev: &Device<device::Bound>, bios: &Vbios, cmd: FwsecCommand) -> Re
>          let ucode = bios.fwsec_image().ucode(&desc)?;
>          let mut dma_object = DmaObject::from_data(dev, ucode)?;
>  
> -        let hdr_offset = usize::from_safe_cast(desc.imem_load_size() + desc.interface_offset());
> +        // Compute hdr_offset = imem_load_size + interface_offset.

I do get the idea behind those comments, but are we sure that's really a good
idea? How do we ensure to keep them up to date in case we have to change the
code?

If we really want this, I'd at least chose a common syntax, e.g.

	// CALC: `imem_load_size + interface_offset`

without the variable name the resulting value is assigned to.

But I'd rather prefer to just drop those comments.

> +        let hdr_offset = desc
> +            .imem_load_size()
> +            .checked_add(desc.interface_offset())
> +            .map(usize::from_safe_cast)
> +            .ok_or(EINVAL)?;
>          // SAFETY: we have exclusive access to `dma_object`.
>          let hdr: &FalconAppifHdrV1 = unsafe { transmute(&dma_object, hdr_offset) }?;