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

["Alexandre Courbot" <acourbot@nvidia.com>]

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.