Re: [PATCH Part1 v5 34/38] x86/sev: Add snp_msg_seqno() helper

[Brijesh Singh]

On 9/9/21 10:43 AM, Peter Gonda wrote:
...

> > Does this address your concern?
>
> So the 'snp_msg_seqno()' call in 'enc_payload' will not increment the
> counter, its only incremented on 'snp_gen_msg_seqno()'? If thats
> correct, that addresses my first concern.

Yes, that is goal.

> > >
> >
> > So far, the only user for the snp_msg_seqno() is the attestation driver.
> > And the driver is designed to serialize the vmgexit request and thus we
> > should not run into concurrence issue.
>
> That seems a little dangerous as any module new code or out-of-tree
> module could use this function thus revealing this race condition
> right? Could we at least have a comment on these functions
> (snp_msg_seqno and snp_gen_msg_seqno) noting this?

Yes, if the driver is not performing the serialization then we will get 
into race condition.

One way to avoid this requirement is to do all the crypto inside the 
snp_issue_guest_request() and eliminate the need to export the 
snp_msg_seqno().

I will add the comment about it in the function.

thanks