Re: [RFC PATCH v1 10/11] virt: coco: arm-cca-host: Publish slot zero and establish streams after acceptance

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Jason Gunthorpe <jgg@nvidia.com> writes:

> On Fri, Nov 13, 2026 at 02:24:59PM +0530, Aneesh Kumar K.V wrote:
>> Jason Gunthorpe <jgg@nvidia.com> writes:
>> 
>> > On Thu, Nov 12, 2026 at 03:07:43PM +0530, Aneesh Kumar K.V wrote:

 [ ... 96 lines skipped ... ] 

> We really want the certificates to be loaded at the start before doing
> key_exchange. That is when they are most useful.
>
> So when we fix this for 1.3 the opt in should trigger a transcript'd
> GET_DIGEST in plain text and certificate collection from all the slots
> in plain text.
>
> 1.3 will sign GET_DIGESTS during KEY_EXCHANGE
> 1.2 RMM could issue CHALLENGE if the device supports it right before
>     KEY_EXCHANGE and transcript it
> 1.2 RMM could issue GET_DIGESTS inside the session and fail if != to
>     the plaintext
>


So the combined flow would be:

Host                             RMM                              Device
|                                 |                                  |
| RMI_PDEV_CREATE(new-flow opt-in)|                                  |
|-------------------------------->|                                  |
|                                 | GET_VERSION / VERSION            |
|                                 | GET_CAPABILITIES / CAPABILITIES  |
|                                 | NEGOTIATE_ALGORITHMS / ALGORITHMS|
|                                 |<-------------------------------->|
| Cache individual VCA messages   |                                  |
|<--------------------------------|                                  |
|                                 |                                  |
|                                 | GET_DIGESTS / DIGESTS [plaintext]|
|                                 |<-------------------------------->|
| Cache discovery transcript      | Retain original slot mask        |
|<--------------------------------| and per-slot chain digests       |
|                                 |                                  |
|                                 | For each populated slot:         |
|                                 | GET_CERTIFICATE / CERTIFICATE    |
|                                 |<-------------------------------->|
| Cache complete chains by slot   |                                  |
|<--------------------------------|                                  |
|                                 |                                  |
|                      Pause: PDEV_NEEDS_KEY                         |
|                                 |                                  |
| Validate candidate certificate  |                                  |
| paths against userspace policy. |                                  |
| Select slot S and extract key S.|                                  |
| Discovery remains provisional.  |                                  |
|                                 |                                  |
| RMI_PDEV_SET_PUBKEY             |                                  |
| (slot S, key S, chain hash S)   |                                  |
|-------------------------------->|                                  |
|                                 |                                  |
|                    IF SPDM 1.2 AND CHALLENGE supported             |
|                                 |                                  |
|                                 | CHALLENGE(slot S, fresh nonce)   |
|                                 |--------------------------------->|
|                                 | CHALLENGE_AUTH                   |
|                                 |<---------------------------------|
|                                 | Verify signature using key S.    |
|                                 | Authenticates earlier DIGESTS.   |
| Cache challenge transcript      |                                  |
|<--------------------------------|                                  |
|                                 |                                  |
|                    END IF                                          |
|                                 |                                  |
|                                 | KEY_EXCHANGE(slot S)             |
|                                 |--------------------------------->|
|                                 | KEY_EXCHANGE_RSP                 |
|                                 |<---------------------------------|
|                                 | Verify signature using key S.    |
|                                 |                                  |
|                    IF SPDM 1.3 multikey negotiated                 |
|                                 |                                  |
|                                 | Signature covers earlier DIGESTS.|
|                                 | Authenticate retained inventory. |
|                                 |                                  |
|                    END IF                                          |
|                                 |                                  |
| Cache key-exchange transcript   |                                  |
|<--------------------------------|                                  |
|                                 | FINISH / FINISH_RSP              |
|                                 |<-------------------------------->|
|                                 | Session established.             |
|                                 |                                  |
|                    IF SPDM 1.2 AND CHALLENGE unavailable           |
|                                 |                                  |
|                                 | GET_DIGESTS / DIGESTS [secure]   |
| Relay ciphertext                |<-------------------------------->|
|                                 | Compare authenticated slot mask  |
|                                 | and every digest with original   |
|                                 | plaintext discovery.             |
|                                 |                                  |
|                                 | Mismatch: fail setup.            |
|                                 | Match: authenticate inventory.   |
|                                 |                                  |
|                    END IF                                          |
|                                 |                                  |
|                                 | Check collected chains against   |
|                                 | authenticated per-slot digests.  |
|                                 |                                  |
|                            PDEV_READY                              |

BTW, all these proposals require RMM changes. As I requested in my previous
email, it would be useful to describe what this would look like without a
firmware change.

-aneesh