Re: [PATCH v4 04/20] gpu: nova-core: vbios: read BitToken using FromBytes

[John Hubbard <jhubbard@nvidia.com>]

On 5/18/26 7:54 PM, Eliot Courtney wrote:
> If `header.token_size` is smaller than `BitToken`, then we currently can
> read past the end of `image.base.data`. Use checked arithmetic for
> computing offsets and simplify reading it in using `FromBytes`.
> 
> Fixes: dc70c6ae2441 ("gpu: nova-core: vbios: Add support to look up PMU table in FWSEC")
> Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
> ---
>  drivers/gpu/nova-core/vbios.rs | 37 ++++++++++++++++++-------------------
>  1 file changed, 18 insertions(+), 19 deletions(-)

Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,
-- 
John Hubbard

> 
> diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
> index 79eb01dabc6f..2ff67273fdff 100644
> --- a/drivers/gpu/nova-core/vbios.rs
> +++ b/drivers/gpu/nova-core/vbios.rs
> @@ -486,7 +486,7 @@ fn new(data: &[u8]) -> Result<Self> {
>  
>  /// BIT Token Entry: Records in the BIT table followed by the BIT header.
>  #[derive(Debug, Clone, Copy)]
> -#[expect(dead_code)]
> +#[repr(C)]
>  struct BitToken {
>      /// 00h: Token identifier
>      id: u8,
> @@ -498,6 +498,9 @@ struct BitToken {
>      data_offset: u16,
>  }
>  
> +// SAFETY: all bit patterns are valid for `BitToken`.
> +unsafe impl FromBytes for BitToken {}
> +
>  // Define the token ID for the Falcon data
>  const BIT_TOKEN_ID_FALCON_DATA: u8 = 0x70;
>  
> @@ -505,32 +508,28 @@ impl BitToken {
>      /// Find a BIT token entry by BIT ID in a PciAtBiosImage
>      fn from_id(image: &PciAtBiosImage, token_id: u8) -> Result<Self> {
>          let header = &image.bit_header;
> +        let entry_size = usize::from(header.token_size);
>  
>          // Offset to the first token entry
>          let tokens_start = image.bit_offset + usize::from(header.header_size);
>  
>          for i in 0..usize::from(header.token_entries) {
> -            let entry_offset = tokens_start + (i * usize::from(header.token_size));
> +            let entry_offset = i
> +                .checked_mul(entry_size)
> +                .and_then(|offset| tokens_start.checked_add(offset))
> +                .ok_or(EINVAL)?;
> +            let entry = image
> +                .base
> +                .data
> +                .get(entry_offset..)
> +                .and_then(|data| data.get(..entry_size))
> +                .ok_or(EINVAL)?;
>  
> -            // Make sure we don't go out of bounds
> -            if entry_offset + usize::from(header.token_size) > image.base.data.len() {
> -                return Err(EINVAL);
> -            }
> +            let (token, _) = BitToken::from_bytes_copy_prefix(entry).ok_or(EINVAL)?;
>  
>              // Check if this token has the requested ID
> -            if image.base.data[entry_offset] == token_id {
> -                return Ok(BitToken {
> -                    id: image.base.data[entry_offset],
> -                    data_version: image.base.data[entry_offset + 1],
> -                    data_size: u16::from_le_bytes([
> -                        image.base.data[entry_offset + 2],
> -                        image.base.data[entry_offset + 3],
> -                    ]),
> -                    data_offset: u16::from_le_bytes([
> -                        image.base.data[entry_offset + 4],
> -                        image.base.data[entry_offset + 5],
> -                    ]),
> -                });
> +            if token.id == token_id {
> +                return Ok(token);
>              }
>          }
>  
>