Re: [PATCH v12 13/22] gpu: nova-core: Hopper/Blackwell: add FMC signature extraction

[Alexandre Courbot]

On Tue Jun 2, 2026 at 5:11 PM JST, Eliot Courtney wrote:
> On Tue Jun 2, 2026 at 12:21 PM JST, John Hubbard wrote:
>> Extract the SHA-384 hash, RSA public key, and RSA signature from the
>> FMC ELF32 firmware sections. FSP Chain of Trust verification needs
>> these to validate the FMC image during boot.
>>
>> Co-developed-by: Alexandre Courbot <acourbot@xxxxxxxxxx>
>> Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx>
>> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
>> ---
>>  drivers/gpu/nova-core/firmware/fsp.rs | 94 ++++++++++++++++++++++++++-
>>  1 file changed, 91 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/nova-core/firmware/fsp.rs b/drivers/gpu/nova-core/firmware/fsp.rs
>> index 011be1e571c2..db61905eac9d 100644
>> --- a/drivers/gpu/nova-core/firmware/fsp.rs
>> +++ b/drivers/gpu/nova-core/firmware/fsp.rs
>> @@ -15,13 +15,35 @@
>>      gpu::Chipset, //
>>  };
>>  
>> +/// Size of the FSP SHA-384 hash, in bytes.
>> +const FSP_HASH_SIZE: usize = 48;
>> +/// Maximum size of the FSP public key (RSA-3072), in bytes.
>> +///
>> +/// The FMC ELF `publickey` section may be shorter, so the remaining bytes are zero-padded.
>> +const FSP_PKEY_SIZE: usize = 384;
>> +/// Maximum size of the FSP signature (RSA-3072), in bytes.
>> +///
>> +/// The FMC ELF `signature` section may be shorter, so the remaining bytes are zero-padded.
>> +const FSP_SIG_SIZE: usize = 384;
>> +
>> +/// Structure to hold FMC signatures.
>> +///
>> +/// C representation is used because this type is used for communication with the FSP.
>> +#[derive(Debug, Clone, Copy)]
>> +#[repr(C)]
>> +pub(crate) struct FmcSignatures {
>> +    pub(crate) hash384: [u8; FSP_HASH_SIZE],
>> +    pub(crate) public_key: [u8; FSP_PKEY_SIZE],
>> +    pub(crate) signature: [u8; FSP_SIG_SIZE],
>> +}
>> +
>>  pub(crate) struct FspFirmware {
>>      /// FMC firmware image data (only the "image" ELF section).
>>      #[expect(dead_code)]
>>      pub(crate) fmc_image: Coherent<[u8]>,
>> -    /// Full FMC ELF for signature extraction.
>> +    /// FMC firmware signatures.
>>      #[expect(dead_code)]
>> -    pub(crate) fmc_elf: Firmware,
>> +    pub(crate) fmc_sigs: KBox<FmcSignatures>,
>>  }
>>  
>>  impl FspFirmware {
>> @@ -41,7 +63,73 @@ pub(crate) fn new(
>>  
>>          Ok(Self {
>>              fmc_image,
>> -            fmc_elf: fw,
>> +            fmc_sigs: Self::extract_fmc_signatures(&fw, dev)?,
>>          })
>>      }
>> +
>> +    /// Extract FMC firmware signatures for Chain of Trust verification.
>> +    ///
>> +    /// Extracts real cryptographic signatures from FMC ELF32 firmware sections.
>> +    /// Returns signatures in a heap-allocated structure to prevent stack overflow.
>> +    fn extract_fmc_signatures(
>> +        fmc_fw: &Firmware,
>> +        dev: &device::Device,
>> +    ) -> Result<KBox<FmcSignatures>> {
>> +        let get_section = |name: &str, max_len: usize| {
>> +            elf::elf_section(fmc_fw.data(), name)
>> +                .ok_or(EINVAL)
>> +                .inspect_err(|_| dev_err!(dev, "FMC firmware missing '{}' section\n", name))
>> +                .and_then(|section| {
>> +                    if section.len() > max_len {
>> +                        dev_err!(
>> +                            dev,
>> +                            "FMC {} section size {} > maximum {}\n",
>> +                            name,
>> +                            section.len(),
>> +                            max_len
>> +                        );
>> +                        Err(EINVAL)
>> +                    } else {
>> +                        Ok(section)
>> +                    }
>> +                })
>> +        };
>> +
>> +        let hash_section = get_section("hash", FSP_HASH_SIZE)?;
>> +        let pkey_section = get_section("publickey", FSP_PKEY_SIZE)?;
>> +        let sig_section = get_section("signature", FSP_SIG_SIZE)?;
>> +
>> +        // The hash section is a SHA-384 output: it must be exactly FSP_HASH_SIZE bytes.
>> +        if hash_section.len() != FSP_HASH_SIZE {
>> +            dev_err!(
>> +                dev,
>> +                "FMC hash section size {} != expected {}\n",
>> +                hash_section.len(),
>> +                FSP_HASH_SIZE
>> +            );
>> +            return Err(EINVAL);
>> +        }
>> +
>> +        // Initialize the signatures in place to avoid building the large `FmcSignatures` on the
>> +        // stack, then fill each section from the firmware.
>> +        let signatures = KBox::init(
>> +            init!(FmcSignatures {
>> +                hash384: [0; _],
>> +                public_key: [0; _],
>> +                signature: [0; _],
>> +            })
>
> This proc macro will generate some code like let field = [0; _]; which
> it then writes into the final init location, so it's stack-ish storage
> although I guess it'll be optimised out.
>
> optional nit: may be better to derive Zeroable and use ..Zeroable::init_zeroed()
> here.
>
> Reviewed-by: Eliot Courtney <ecourtney@xxxxxxxxxx>

Yup, this was also picked up by Sashiko. I ended up doing exactly what
you suggested [1].

[1] https://lore.kernel.org/all/DIYEINL9REVG.3484XPOLDZ0KJ@xxxxxxxxxx/