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

[Joel Fernandes <joelagnelf@nvidia.com>]

On 1/28/2026 3:08 AM, Alexandre Courbot wrote:
> On Wed Jan 28, 2026 at 4:58 PM JST, Alexandre Courbot wrote:
>> On Tue Jan 27, 2026 at 5:23 AM JST, Joel Fernandes wrote:
>>> Use checked_add() and checked_mul() when computing offsets from
>>> firmware-provided values in new_fwsec().
>>>
>>> Without checked arithmetic, corrupt firmware could cause integer overflow. The
>>> danger is not just wrapping to a huge value, but potentially wrapping to a
>>> small plausible offset that passes validation yet accesses entirely wrong data,
>>> causing silent corruption or security issues.
>>>
>>> Reviewed-by: Zhi Wang <zhiw@nvidia.com>
>>> Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
>>> ---
>>>   drivers/gpu/nova-core/firmware/fwsec.rs | 60 ++++++++++++++-----------
>>>   1 file changed, 35 insertions(+), 25 deletions(-)
>>>
>>> diff --git a/drivers/gpu/nova-core/firmware/fwsec.rs b/drivers/gpu/nova-core/firmware/fwsec.rs
>>> index a8ec08a500ac..71541b1f07d7 100644
>>> --- a/drivers/gpu/nova-core/firmware/fwsec.rs
>>> +++ b/drivers/gpu/nova-core/firmware/fwsec.rs
>>> @@ -46,10 +46,7 @@
>>>           Signed,
>>>           Unsigned, //
>>>       },
>>> -    num::{
>>> -        FromSafeCast,
>>> -        IntoSafeCast, //
>>> -    },
>>> +    num::FromSafeCast,
>>>       vbios::Vbios,
>>>   };
>>>   
>>> @@ -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.
>>> +        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`.
>>
>> Missing empty line before the SAFETY comment (also in other places).
>>
>> I will fix when applying, no need to resend.
> 
> I also got this clippy warning when building:
> 
> 		warning: unsafe block missing a safety comment
> 			--> ../drivers/gpu/nova-core/firmware/fwsec.rs:303:17
> 				|
> 		303 |                 unsafe { transmute_mut(&mut dma_object, dmem_mapper_offset) }?;
> 				|                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 				|
> 				= help: consider adding a safety comment on the preceding line
> 				= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#undocumented_unsafe_blocks
> 				= note: requested on the command line with `-W clippy::undocumented-unsafe-blocks`
> 
> 		warning: unsafe block missing a safety comment
> 			--> ../drivers/gpu/nova-core/firmware/fwsec.rs:319:17
> 				|
> 		319 |                 unsafe { transmute_mut(&mut dma_object, frts_cmd_offset) }?;
> 				|                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 				|
> 				= help: consider adding a safety comment on the preceding line
> 				= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#undocumented_unsafe_blocks
> 
> 		warning: 2 warnings emitted
> 
> Since the `unsafe` keyword has moved to a new line, its SAFETY comment needed
> to be moved right above it, despite it still being part of the same statement.
> I'll fix this as well.

Thanks Alex! Do you mind also dropping those "Compute .." comments that 
Danilo mentioned. But come to think of it, I think those comments do 
improve any loss of readability due to the checked_* calls.

--
Joel Fernandes