[RFC] SPDM attestation E2E findings from Renode testing

[Matt Johnston]

Hi Gary,

On Wed, 2026-04-01 at 21:35 +0000, Gary Beihl wrote:
> 
> 
> (c) Shared AF_MCTP socket (affects 80311: mctp_helper.hpp)
>  
> Only one socket can bind to (MCTP_ADDR_ANY, MCTP_TYPE_SPDM).  When spdmd
> attests multiple endpoints sequentially, the second
>   MctpIoClass::createSocket() fails with EADDRINUSE. The fix is a process-
> lifetime shared socket (singleton pattern), draining stale responses
> between endpoint attestations with recv(MSG_DONTWAIT).

Since Linux 6.17 it is possible to restrict a bind() to only receive from a
single remote endpoint [1]. Call connect() with the remote address before the
bind().

Is the SPDM implementation using asynchronous messages sent by the responder?
(KEY_UPDATE, HEARTBEAT, END_SESSION)
If not, I think the bind() could be removed altogether.
bind() isn't needed in the case where the Linux host is performing a plain
send() then receiving a response. A similar situation was fixed in pldmtool
[2].

[1] https://lore.kernel.org/all/20250710-mctp-bind-v4-6-8ec2f6460c56@codeconstruct.com.au/
[2] https://gerrit.openbmc.org/c/openbmc/pldm/+/83626 

Cheers,
Matt

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