Re: [PATCH v3 02/11] gpu: nova-core: vbios: limit `BitToken` entry reads

Eliot Courtney
2026-05-01T05:38:34Z

On Wed Apr 29, 2026 at 10:35 PM JST, Alexandre Courbot wrote:
> On Tue Apr 21, 2026 at 5:20 PM JST, Eliot Courtney wrote:
>> If `header.token_size` is smaller than `BitToken`, then we currently can
>> read past the end of `image.base.data`. Check that the token size is at
>> least as big as `BitToken`.
>>
>> Fixes: dc70c6ae2441 ("gpu: nova-core: vbios: Add support to look up PMU table in FWSEC")
>> Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
>> Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
>> ---
>> drivers/gpu/nova-core/vbios.rs | 34 +++++++++++++++++-----------------
>> 1 file changed, 17 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/gpu/nova-core/vbios.rs b/drivers/gpu/nova-core/vbios.rs
>> index 6de7e58e0da0..de856000de23 100644
>> --- a/drivers/gpu/nova-core/vbios.rs
>> +++ b/drivers/gpu/nova-core/vbios.rs
>> @@ -423,31 +423,31 @@ 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);
>> +
>> + if entry_size < size_of::<BitToken>() {
>> + return Err(EINVAL);
>> + }
>
> You can get rid of this check if you convert the code as suggested
> below.
>
>>
>> // 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));
>> -
>> - // 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 entry_offset = tokens_start + (i * entry_size);
>
> Should we use checked arithmetic here?
>
>> + let entry = image
>> + .base
>> + .data
>> + .get(entry_offset..)
>> + .and_then(|data| data.get(..entry_size))
>> + .ok_or(EINVAL)?;
>>
>> // Check if this token has the requested ID
>> - if image.base.data[entry_offset] == token_id {
>> + if entry[0] == 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],
>> - ]),
>> + id: entry[0],
>> + data_version: entry[1],
>> + data_size: u16::from_le_bytes([entry[2], entry[3]]),
>> + data_offset: u16::from_le_bytes([entry[4], entry[5]]),
>
> A common pattern in this file (with several such sites still to fix), is
> that since Nova only supports little-endian we can leverage `FromBytes`
> in order to avoid all these `from_le_bytes` call. Here this would look
> as follows:
>
> for i in 0..usize::from(header.token_entries) {
> let entry_offset = i
> .checked_mul(entry_size)
> .and_then(|off| tokens_start.checked_add(off))
> .ok_or(EINVAL)?;
>
> let entry = image
> .base
> .data
> .get(entry_offset..entry_offset + entry_size)
> .and_then(|data| data.get(..entry_size))
> .ok_or(EINVAL)?;
>
> let (token, _) = BitToken::from_bytes_copy_prefix(entry).ok_or(EINVAL)?;
>
> if token.id == token_id {
> return Ok(token);
> }
> }
>
> which has several benefits:
>
> - No error-prone `entry[index]` accesses,
> - The size check on `entry_size` is done for free by
> `from_bytes_copy_prefix`, and the slice bounds cannot be wrong,
> - Shorter, more readable code overall.
>
> Unfortunately we cannot just use `from_bytes_prefix` because we don't
> have any alignment guarantee, but this is still an improvement IMHO.
>
> If you go that way and derive `FromBytes` on `BitToken`, don't forget to
> also make it `#[repr(C)]`. :)

I agree this is better, thanks!