Re: [RFC v3 15/27] lib: rspdm: Support SPDM get_digests

[Jonathan Cameron]

On Wed, 11 Feb 2026 13:29:22 +1000
alistair23@xxxxxxxxx wrote:

> From: Alistair Francis <alistair@xxxxxxxxxxxxx>
> 
> Support the GET_DIGESTS SPDM command.
> 
> Signed-off-by: Alistair Francis <alistair@xxxxxxxxxxxxx>
A few things inline.

Thanks,

J 
> diff --git a/lib/rspdm/state.rs b/lib/rspdm/state.rs
> index d0b10f27cd9c..2606b825c494 100644
> --- a/lib/rspdm/state.rs
> +++ b/lib/rspdm/state.rs


>  /// The current SPDM session state for a device. Based on the
> @@ -54,6 +54,10 @@
>  ///  Selected by responder during NEGOTIATE_ALGORITHMS exchange.
>  /// @meas_hash_alg: Hash algorithm for measurement blocks.
>  ///  Selected by responder during NEGOTIATE_ALGORITHMS exchange.
> +/// @supported_slots: Bitmask of responder's supported certificate slots.
> +///  Received during GET_DIGESTS exchange (from SPDM 1.3).
> +/// @provisioned_slots: Bitmask of responder's provisioned certificate slots.
> +///  Received during GET_DIGESTS exchange.
>  /// @base_asym_enc: Human-readable name of @base_asym_alg's signature encoding.
>  ///  Passed to crypto subsystem when calling verify_signature().
>  /// @sig_len: Signature length of @base_asym_alg (in bytes).
> @@ -68,6 +72,9 @@
>  /// @desc: Synchronous hash context for @base_hash_alg computation.
>  /// @hash_len: Hash length of @base_hash_alg (in bytes).
>  ///  H in SPDM specification.
> +/// @slot: Certificate chain in each of the 8 slots.  NULL pointer if a slot is
> +///  not populated.  Prefixed by the 4 + H header per SPDM 1.0.0 table 15.
> +/// @slot_sz: Certificate chain size (in bytes).

That's not matching the code..

>  #[expect(dead_code)]
>  pub struct SpdmState {
>      pub(crate) dev: *mut bindings::device,
> @@ -83,6 +90,8 @@ pub struct SpdmState {
>      pub(crate) base_asym_alg: u32,
>      pub(crate) base_hash_alg: u32,
>      pub(crate) meas_hash_alg: u32,
> +    pub(crate) supported_slots: u8,
> +    pub(crate) provisioned_slots: u8,
>  
>      /* Signature algorithm */
>      base_asym_enc: &'static CStr,
> @@ -93,6 +102,9 @@ pub struct SpdmState {
>      pub(crate) shash: *mut bindings::crypto_shash,
>      pub(crate) desc: Option<&'static mut bindings::shash_desc>,
>      pub(crate) hash_len: usize,
> +
> +    // Certificates
> +    pub(crate) certs: [KVec<u8>; SPDM_SLOTS],
>  }

> @@ -539,4 +554,70 @@ pub(crate) fn negotiate_algs(&mut self) -> Result<(), Error> {
>  
>          Ok(())
>      }
> +
> +    pub(crate) fn get_digests(&mut self) -> Result<(), Error> {
> +        let mut request = GetDigestsReq::default();
> +        request.version = self.version;
> +
> +        let req_sz = core::mem::size_of::<GetDigestsReq>();
> +        let rsp_sz = core::mem::size_of::<GetDigestsRsp>() + SPDM_SLOTS * self.hash_len;
> +
> +        // SAFETY: `request` is repr(C) and packed, so we can convert it to a slice
> +        let request_buf = unsafe { from_raw_parts_mut(&mut request as *mut _ as *mut u8, req_sz) };
> +
> +        let mut response_vec: KVec<u8> = KVec::with_capacity(rsp_sz, GFP_KERNEL)?;
> +        // SAFETY: `request` is repr(C) and packed, so we can convert it to a slice
> +        let response_buf = unsafe { from_raw_parts_mut(response_vec.as_mut_ptr(), rsp_sz) };
> +
> +        let rc = self.spdm_exchange(request_buf, response_buf)?;
> +
> +        if rc < (core::mem::size_of::<GetDigestsRsp>() as i32) {
> +            pr_err!("Truncated digests response\n");
> +            to_result(-(bindings::EIO as i32))?;
> +        }
> +
> +        // SAFETY: `rc` is the length of data read, which will be smaller
> +        // then the capacity of the vector
> +        unsafe { response_vec.inc_len(rc as usize) };
> +
> +        let response: &mut GetDigestsRsp = Untrusted::new_mut(&mut response_vec).validate_mut()?;
> +
> +        if rc

Perhaps another local variable to represent what this is better than the rc name does?

> +            < (core::mem::size_of::<GetDigestsReq>()
> +                + response.param2.count_ones() as usize * self.hash_len) as i32
> +        {
> +            pr_err!("Truncated digests response\n");
> +            to_result(-(bindings::EIO as i32))?;
> +        }
> +
> +        let mut deprovisioned_slots = self.provisioned_slots & !response.param2;
> +        while (deprovisioned_slots.trailing_zeros() as usize) < SPDM_SLOTS {
> +            let slot = deprovisioned_slots.trailing_zeros() as usize;
> +            self.certs[slot].clear();
> +            deprovisioned_slots &= !(1 << slot);
> +        }
> +
> +        self.provisioned_slots = response.param2;
> +        if self.provisioned_slots == 0 {
> +            pr_err!("No certificates provisioned\n");
> +            to_result(-(bindings::EPROTO as i32))?;
> +        }
> +
> +        if self.version >= 0x13 && (response.param2 & !response.param1 != 0) {

Should we use the define for the version?

> +            pr_err!("Malformed digests response\n");
> +            to_result(-(bindings::EPROTO as i32))?;
> +        }
> +
> +        let supported_slots = if self.version >= 0x13 {
> +            response.param1
> +        } else {
> +            0xFF
> +        };
> +
> +        if self.supported_slots != supported_slots {
> +            self.supported_slots = supported_slots;

Why not set it unconditionally? Is this expected to have
side effects?

> +        }
> +
> +        Ok(())
> +    }
>  }
> diff --git a/lib/rspdm/validator.rs b/lib/rspdm/validator.rs
> index 036a077c71c3..2150a23997db 100644
> --- a/lib/rspdm/validator.rs
> +++ b/lib/rspdm/validator.rs

> +
> +#[repr(C, packed)]
> +pub(crate) struct GetDigestsRsp {
> +    pub(crate) version: u8,
> +    pub(crate) code: u8,
> +    pub(crate) param1: u8,
> +    pub(crate) param2: u8,
> +
> +    pub(crate) digests: __IncompleteArrayField<u8>,
Maybe include KeyPairIDs, certificatinfo, and KeyUsageMask
in this structure definition (1.3.1 has them)
Or at very least a comment to say they are a job for another day.

None of those exist yet as we didn't ask for MULTI_KEY_CAP.

> +}
> +
> +impl Validate<&mut Unvalidated<KVec<u8>>> for &mut GetDigestsRsp {
> +    type Err = Error;
> +
> +    fn validate(unvalidated: &mut Unvalidated<KVec<u8>>) -> Result<Self, Self::Err> {
> +        let raw = unvalidated.raw_mut();
> +        if raw.len() < mem::size_of::<GetDigestsRsp>() {
> +            return Err(EINVAL);
> +        }
> +
> +        let ptr = raw.as_mut_ptr();
> +        // CAST: `GetDigestsRsp` only contains integers and has `repr(C)`.
> +        let ptr = ptr.cast::<GetDigestsRsp>();
> +        // SAFETY: `ptr` came from a reference and the cast above is valid.
> +        let rsp: &mut GetDigestsRsp = unsafe { &mut *ptr };
> +
> +        Ok(rsp)
> +    }
> +}