Re: [RFC v3 16/27] lib: rspdm: Support SPDM get_certificate

[Alistair Francis]

On Wed, Mar 4, 2026 at 12:51 AM Jonathan Cameron
<jonathan.cameron@xxxxxxxxxx> wrote:
>
> On Wed, 11 Feb 2026 13:29:23 +1000
> alistair23@xxxxxxxxx wrote:
>
> > From: Alistair Francis <alistair@xxxxxxxxxxxxx>
> >
> > Support the GET_CERTIFICATE SPDM command.
> >
> > Signed-off-by: Alistair Francis <alistair@xxxxxxxxxxxxx>
>
> Minor things inline. The endian handling in general needs
> some care + possibly some tests.
>
> > diff --git a/lib/rspdm/state.rs b/lib/rspdm/state.rs
> > index 2606b825c494..1e5656144611 100644
> > --- a/lib/rspdm/state.rs
> > +++ b/lib/rspdm/state.rs
> > @@ -26,8 +26,9 @@
> >      SPDM_REQ, SPDM_RSP_MIN_CAPS, SPDM_SLOTS, SPDM_VER_10, SPDM_VER_11, SPDM_VER_12,
> >  };
>
> >  impl SpdmState {
> >      pub(crate) fn new(
> >          dev: *mut bindings::device,
> > @@ -620,4 +629,118 @@ pub(crate) fn get_digests(&mut self) -> Result<(), Error> {
> >
> >          Ok(())
> >      }
> > +
> > +    fn get_cert_exchange(
> > +        &mut self,
> > +        request_buf: &mut [u8],
> > +        response_vec: &mut KVec<u8>,
> > +        rsp_sz: usize,
> > +    ) -> Result<&mut GetCertificateRsp, Error> {
> > +        // 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::<GetCertificateReq>() as i32) {
> > +            pr_err!("Truncated certificate 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 GetCertificateRsp = Untrusted::new_mut(response_vec).validate_mut()?;
> > +
> > +        if rc
> > +            < (core::mem::size_of::<GetCertificateRsp>() + response.portion_length as usize) as i32
>
> As below, I'd keep the type matching the spec and have the little endian to cpu conversion out here.
>
>
> > +        {
> > +            pr_err!("Truncated certificate response\n");
> > +            to_result(-(bindings::EIO as i32))?;
> > +        }
> > +
> > +        Ok(response)
> > +    }
> > +
> > +    pub(crate) fn get_certificate(&mut self, slot: u8) -> Result<(), Error> {
> > +        let mut request = GetCertificateReq::default();
> > +        request.version = self.version;
> > +        request.param1 = slot;
> > +
> > +        let req_sz = core::mem::size_of::<GetCertificateReq>();
> > +        let rsp_sz = ((core::mem::size_of::<GetCertificateRsp>() + 0xffff) as u32)
>
> Similar to earlier comment, do we have U16_MAX or similar available?
>
> > +            .min(self.transport_sz) as usize;
> > +
> > +        request.offset = 0;
>
> That's the default, so worth setting here?

I like being explicit :)

>
> > +        request.length = (rsp_sz - core::mem::size_of::<GetCertificateRsp>()).to_le() as u16;
>
> Why store it in a u16 if it is le16?

core::mem::size_of gives us a usize. So this ensures it's little
endian then casts it to a u16.

We could cast it to a __le16. u16 is a standard Rust type (compared to
__le16 which is a internal kernel type), so I prefer u16 as it matches
other Rust implementations.

>
> > +
> > +        // 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)?;
> > +
> > +        let response = self.get_cert_exchange(request_buf, &mut response_vec, rsp_sz)?;
> > +
> > +        let total_cert_len =
> > +            ((response.portion_length + response.remainder_length) & 0xFFFF) as usize;
> > +
> > +        let mut certs_buf: KVec<u8> = KVec::new();
> > +
> > +        certs_buf.extend_from_slice(
> > +            &response_vec[8..(8 + response.portion_length as usize)],
> > +            GFP_KERNEL,
> > +        )?;
> > +
> > +        let mut offset: usize = response.portion_length as usize;
> > +        let mut remainder_length = response.remainder_length as usize;
> > +
> > +        while remainder_length > 0 {
> > +            request.offset = offset.to_le() as u16;
>
> Similar to other places, why not just make the type __le16
> and avoid need to cast.

Same as above

>
> > +            request.length = (remainder_length
> > +                .min(rsp_sz - core::mem::size_of::<GetCertificateRsp>()))
> > +            .to_le() as u16;
>
> Likewise.

and above

>
> > +
> > +            let request_buf =
> > +                unsafe { from_raw_parts_mut(&mut request as *mut _ as *mut u8, req_sz) };
> > +
> > +            let response = self.get_cert_exchange(request_buf, &mut response_vec, rsp_sz)?;
> > +
> > +            if response.portion_length == 0
> > +                || (response.param1 & 0xF) != slot
> > +                || offset as u16 + response.portion_length + response.remainder_length
> > +                    != total_cert_len as u16
> > +            {
> > +                pr_err!("Malformed certificate response\n");
> > +                to_result(-(bindings::EPROTO as i32))?;
> > +            }
> > +
> > +            certs_buf.extend_from_slice(
> > +                &response_vec[8..(8 + response.portion_length as usize)],
> > +                GFP_KERNEL,
> > +            )?;
> > +            offset += response.portion_length as usize;
> > +            remainder_length = response.remainder_length as usize;
> > +        }
> > +
> > +        let header_length = core::mem::size_of::<SpdmCertChain>() + self.hash_len;
> > +
> > +        let ptr = certs_buf.as_mut_ptr();
> > +        // SAFETY: `SpdmCertChain` is repr(C) and packed, so we can convert it from a slice
> > +        let ptr = ptr.cast::<SpdmCertChain>();
> > +        // SAFETY: `ptr` came from a reference and the cast above is valid.
> > +        let certs: &mut SpdmCertChain = unsafe { &mut *ptr };
> > +
> > +        if total_cert_len < header_length
> > +            || total_cert_len != usize::from_le(certs.length as usize)
>
> That's a confusing bit of casting as you are interpretting an __le16 as a usize
> before doing the endian conversion?  Seems unlikely to get what you want
> on a big endian machine.

Yeah, I think this is wrong

>
> > +            || total_cert_len != certs_buf.len()
> > +        {
> > +            pr_err!("Malformed certificate chain in slot {slot}\n");
> > +            to_result(-(bindings::EPROTO as i32))?;
> > +        }
> > +
> > +        self.certs[slot as usize].clear();
> > +        self.certs[slot as usize].extend_from_slice(&certs_buf, GFP_KERNEL)?;
> > +
> > +        Ok(())
> > +    }
> >  }
> > diff --git a/lib/rspdm/validator.rs b/lib/rspdm/validator.rs
> > index 2150a23997db..a8bc3378676f 100644
> > --- a/lib/rspdm/validator.rs
> > +++ b/lib/rspdm/validator.rs
> > @@ -17,8 +17,9 @@
> >  };
>
> >  #[repr(C, packed)]
> > @@ -364,3 +365,62 @@ fn validate(unvalidated: &mut Unvalidated<KVec<u8>>) -> Result<Self, Self::Err>
> >          Ok(rsp)
> >      }
> >  }
>
> > +#[repr(C, packed)]
> > +pub(crate) struct GetCertificateRsp {
> > +    pub(crate) version: u8,
> > +    pub(crate) code: u8,
> > +    pub(crate) param1: u8,
> > +    pub(crate) param2: u8,
> > +
> > +    pub(crate) portion_length: u16,
> > +    pub(crate) remainder_length: u16,
> > +
> > +    pub(crate) cert_chain: __IncompleteArrayField<u8>,
> > +}
> > +
> > +impl Validate<&mut Unvalidated<KVec<u8>>> for &mut GetCertificateRsp {
> > +    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::<GetCertificateRsp>() {
> > +            return Err(EINVAL);
> > +        }
> > +
> > +        let ptr = raw.as_mut_ptr();
> > +        // CAST: `GetCertificateRsp` only contains integers and has `repr(C)`.
> > +        let ptr = ptr.cast::<GetCertificateRsp>();
> > +        // SAFETY: `ptr` came from a reference and the cast above is valid.
> > +        let rsp: &mut GetCertificateRsp = unsafe { &mut *ptr };
> > +
> > +        rsp.portion_length = rsp.portion_length.to_le();
> > +        rsp.remainder_length = rsp.remainder_length.to_le();
>
> Why to_le()?  I can understand from_le() but then I'm a bit dubious about the
> types. My gut feeling is that the validate code should leave these in little
> endian and we should convert them only at time of use.

Fixed

Alistair

>
> > +
> > +        Ok(rsp)
> > +    }
> > +}
>