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

From: "Danilo Krummrich" <dakr@kernel.org>
To: "Joel Fernandes" <joelagnelf@nvidia.com>
Cc: linux-kernel@vger.kernel.org, "Paul Walmsley" <pjw@kernel.org>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Alexandre Ghiti" <alex@ghiti.fr>,
	"Miguel Ojeda" <ojeda@kernel.org>,
	"Boqun Feng" <boqun.feng@gmail.com>,
	"Gary Guo" <gary@garyguo.net>,
	"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
	"Benno Lossin" <lossin@kernel.org>,
	"Andreas Hindborg" <a.hindborg@kernel.org>,
	"Alice Ryhl" <aliceryhl@google.com>,
	"Trevor Gross" <tmgross@umich.edu>,
	"Alexandre Courbot" <acourbot@nvidia.com>,
	"John Hubbard" <jhubbard@nvidia.com>,
	"Alistair Popple" <apopple@nvidia.com>,
	"Timur Tabi" <ttabi@nvidia.com>, "Edwin Peer" <epeer@nvidia.com>,
	"Zhi Wang" <zhiw@nvidia.com>, "David Airlie" <airlied@gmail.com>,
	"Simona Vetter" <simona@ffwll.ch>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Alex Gaynor" <alex.gaynor@gmail.com>,
	"Dirk Behme" <dirk.behme@gmail.com>,
	nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	rust-for-linux@vger.kernel.org, linux-riscv@lists.infradead.org
Subject: Re: [PATCH v2 1/5] gpu: nova-core: use checked arithmetic in FWSEC firmware parsing
Date: Wed, 28 Jan 2026 11:53:48 +0100	[thread overview]
Message-ID: <DG0607SU943F.1FDOPYPN38FCS@kernel.org> (raw)
In-Reply-To: <20260126202305.2526618-2-joelagnelf@nvidia.com>

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) }?;

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