Re: [PATCH v3 5/8] gpu: nova-core: add NVKV decoder

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] nova-core: NVKV decode corrupts array layouts on big-endian hosts
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commit 561207bfbca10da1af8ade9ea863d375b4883ed5
Author: Eliot Courtney <ecourtney@nvidia.com>

gpu: nova-core: add NVKV decoder

Add a decoder for NVKV. This is for receiving messages from GSP for
GMCAPI calls. The NVKV format essentially encodes a sequence of function
calls f(key, index, value).

> diff --git a/drivers/gpu/nova-core/gsp/nvkv/decode.rs b/drivers/gpu/nova-core/gsp/nvkv/decode.rs
> new file mode 100644
> index 0000000000000..c4c24fe1108e9
> --- /dev/null
> +++ b/drivers/gpu/nova-core/gsp/nvkv/decode.rs
[ ... ]
> +    /// Takes `count` bytes. If `count` is not a multiple of 8 (`u64` size), bytes are discarded up
> +    /// to the next multiple.
> +    fn take_u8s(&mut self, count: usize) -> Result<&'a [u8]> {
> +        let values = self.take_u64s(count.div_ceil(8))?;
> +        values.as_bytes().get(..count).ok_or(EINVAL)

[Severity: High]
Does Cursor::take_u8s() in drivers/gpu/nova-core/gsp/nvkv/decode.rs handle
big-endian architectures correctly?

Directly casting native u64 memory to u8 slices yields the bytes in reverse
order within each 64-bit word on big-endian systems.

This could cause the NVKV protocol to fail to correctly decode (and encode)
`Array8` arrays, causing GPU initialization (GSP RPC) to fail completely or
receive corrupted data.

> +    }
> +
> +    /// Takes `count` 32-bit values. If `count` is not a multiple of 2 (`u64` size), bytes are
> +    /// discarded up to the next multiple.
> +    fn take_u32s(&mut self, count: usize) -> Result<&'a [u32]> {
> +        let values = self.take_u64s(count.div_ceil(2))?;
> +        <[u32]>::ref_from_prefix_with_elems(values.as_bytes(), count)

[Severity: High]
Can Cursor::take_u32s() corrupt array layouts on big-endian hosts?

Directly mapping native-endian u64 memory to u32 slices swaps the order of
packed elements on big-endian systems (e.g., swapping the first and second
32-bit values within the 64-bit word).

This defect prevents correctly decoding `Array32` and `Seq32` arrays on these
platforms.

> +            .map(|(elems, _)| elems)
> +            .map_err(|_| EINVAL)
> +    }

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Sashiko AI review · https://sashiko.dev/#/patchset/20260928-b4-nvkv-v3-0-f04504c262c2@nvidia.com?part=5