Re: [PATCH 21/31] gpu: nova-core: Hopper/Blackwell: add FMC signature extraction

[Joel Fernandes <joelagnelf@nvidia.com>]

Hi John,

On 12/3/2025 12:59 AM, John Hubbard wrote:
> Add extract_fmc_signatures_static() to parse cryptographic signatures
> from FMC ELF firmware sections. This extracts the SHA-384 hash, RSA
> public key, and signature needed for Chain of Trust verification.
> 
> Also exposes the elf_section() helper from firmware.rs for use by FSP.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  drivers/gpu/nova-core/firmware.rs |   4 +-
>  drivers/gpu/nova-core/fsp.rs      | 104 ++++++++++++++++++++++++++++++
>  2 files changed, 107 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/nova-core/firmware.rs b/drivers/gpu/nova-core/firmware.rs
> index 5cbb8be7434f..7f8d62f9ceba 100644
> --- a/drivers/gpu/nova-core/firmware.rs
> +++ b/drivers/gpu/nova-core/firmware.rs
> @@ -23,6 +23,8 @@
>      },
>  };
>  
> +pub(crate) use elf::elf_section;
> +
>  pub(crate) mod booter;
>  pub(crate) mod fsp;
>  pub(crate) mod fwsec;
> @@ -419,7 +421,7 @@ fn elf32_section<'a>(elf: &'a [u8], name: &str) -> Option<&'a [u8]> {
>      }
>  
>      /// Automatically detects ELF32 vs ELF64 based on the ELF header.
> -    pub(super) fn elf_section<'a>(elf: &'a [u8], name: &str) -> Option<&'a [u8]> {
> +    pub(crate) fn elf_section<'a>(elf: &'a [u8], name: &str) -> Option<&'a [u8]> {
>          // Check ELF magic.
>          if elf.len() < 5 || elf.get(0..4)? != b"\x7fELF" {
>              return None;
> diff --git a/drivers/gpu/nova-core/fsp.rs b/drivers/gpu/nova-core/fsp.rs
> index 389c43bfd538..311b6d4c6011 100644
> --- a/drivers/gpu/nova-core/fsp.rs
> +++ b/drivers/gpu/nova-core/fsp.rs
> @@ -256,4 +256,108 @@ pub(crate) fn wait_secure_boot(
>          })
>          .map(|_| ())
>      }
> +
> +    /// 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.
> +    pub(crate) fn extract_fmc_signatures_static(
> +        dev: &device::Device<device::Bound>,
> +        fmc_fw_data: &[u8],
> +    ) -> Result<KBox<FmcSignatures>> {
> +        dev_dbg!(dev, "FMC firmware size: {} bytes\n", fmc_fw_data.len());

Let us remove these? I think we discussed [1] that once things are working, we'd
not want these and can add it on-demand if needed.

[1] https://lore.kernel.org/all/d6c9c7f2-098e-4b55-b754-4287b698fc1c@nvidia.com/

> +
> +        // Extract hash section (SHA-384)
> +        let hash_section = crate::firmware::elf_section(fmc_fw_data, "hash")
> +            .ok_or(EINVAL)
> +            .inspect_err(|_| dev_err!(dev, "FMC firmware missing 'hash' section\n"))?;
> +
> +        // Extract public key section (RSA public key)
> +        let pkey_section = crate::firmware::elf_section(fmc_fw_data, "publickey")
> +            .ok_or(EINVAL)
> +            .inspect_err(|_| dev_err!(dev, "FMC firmware missing 'publickey' section\n"))?;
> +
> +        // Extract signature section (RSA signature)
> +        let sig_section = crate::firmware::elf_section(fmc_fw_data, "signature")
> +            .ok_or(EINVAL)
> +            .inspect_err(|_| dev_err!(dev, "FMC firmware missing 'signature' section\n"))?;
> +
> +        dev_dbg!(
> +            dev,
> +            "FMC ELF sections: hash={} bytes, pkey={} bytes, sig={} bytes\n",
> +            hash_section.len(),
> +            pkey_section.len(),
> +            sig_section.len()
> +        );
> +

Here as well.

> +        // Validate section sizes - hash must be exactly 48 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);
> +        }
> +
> +        // Public key and signature can be smaller than the fixed array sizes
> +        if pkey_section.len() > FSP_PKEY_SIZE * 4 {
> +            dev_err!(
> +                dev,
> +                "FMC publickey section size {} > maximum {}\n",
> +                pkey_section.len(),
> +                FSP_PKEY_SIZE * 4
> +            );
> +            return Err(EINVAL);
> +        }
> +
> +        if sig_section.len() > FSP_SIG_SIZE * 4 {
> +            dev_err!(
> +                dev,
> +                "FMC signature section size {} > maximum {}\n",
> +                sig_section.len(),
> +                FSP_SIG_SIZE * 4
> +            );
> +            return Err(EINVAL);
> +        }
> +
> +        // Allocate signature structure on heap to avoid stack overflow
> +        let mut signatures = KBox::new(FmcSignatures::default(), GFP_KERNEL)?;
> +
> +        // Copy hash section directly as bytes (48 bytes exactly)
> +        // SAFETY: hash384 is a [u32; 12] array (48 bytes), and we create a byte slice of
> +        // exactly FSP_HASH_SIZE (48) bytes. The pointer is valid and properly aligned.
> +        let hash_bytes = unsafe {
> +            core::slice::from_raw_parts_mut(
> +                signatures.hash384.as_mut_ptr().cast::<u8>(),
> +                FSP_HASH_SIZE,
> +            )
> +        };
> +        hash_bytes.copy_from_slice(hash_section);
> +
> +        // Copy public key section (up to 388 bytes, zero-padded)
> +        // SAFETY: public_key is a [u32; 96] array (384 bytes), and we create a byte slice of
> +        // FSP_PKEY_SIZE * 4 bytes. The pointer is valid and properly aligned.
> +        let pkey_bytes = unsafe {
> +            core::slice::from_raw_parts_mut(
> +                signatures.public_key.as_mut_ptr().cast::<u8>(),
> +                FSP_PKEY_SIZE * 4,
> +            )
> +        };
> +        pkey_bytes[..pkey_section.len()].copy_from_slice(pkey_section);

Even if this works in practice, I believe it's UB as the `from_raw_parts_mut()`
should have the entire slice range to be valid memory (see [2]), but
FSP_PKEY_SIZE * 4 is 388 bytes while public_key is only 384 bytes ([u32; 96]).
This is vulnerable as the KBox holding the signature may not have the extra
space even if it does now.

Can we create a slice with exactly the bytes we need? something like:
let pkey_bytes = unsafe {
    core::slice::from_raw_parts_mut(
        signatures.public_key.as_mut_ptr().cast::<u8>(),
        pkey_section.len(),
    )
};
pkey_bytes.copy_from_slice(pkey_section);

Another reason for doing this is, the code is more fragile left as is, as there
is a risk of unrelated memory leaking into the slice and accessed by new/future
code.

[2] "Behavior is undefined if any of the following conditions are violated"
https://doc.rust-lang.org/std/slice/fn.from_raw_parts_mut.html

thanks,

 - Joel

> +
> +        // Copy signature section (up to 384 bytes, zero-padded)
> +        // SAFETY: signature is a [u32; 96] array (384 bytes), and we create a byte slice of
> +        // FSP_SIG_SIZE * 4 bytes. The pointer is valid and properly aligned.
> +        let sig_bytes = unsafe {
> +            core::slice::from_raw_parts_mut(
> +                signatures.signature.as_mut_ptr().cast::<u8>(),
> +                FSP_SIG_SIZE * 4,
> +            )
> +        };
> +        sig_bytes[..sig_section.len()].copy_from_slice(sig_section);
> +
> +        Ok(signatures)
> +    }
>  }