linux-kernel - Re: [PATCH] tpm: Document UEFI event log quirks

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Message-ID: <846cacae8cede764a2e84f628f539d94582fdbe0.camel@linux.intel.com>
Date:   Mon, 08 Jul 2019 18:25:38 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org,
        linux-integrity@...r.kernel.org, linux-doc@...r.kernel.org
Cc:     tweek@...gle.com, matthewgarrett@...gle.com,
        Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH] tpm: Document UEFI event log quirks

On Sun, 2019-07-07 at 12:33 -0700, Randy Dunlap wrote:
> On 7/5/19 3:15 AM, Jarkko Sakkinen wrote:
> > On Wed, 2019-07-03 at 09:45 -0700, Randy Dunlap wrote:
> > > > +This introduces another problem: nothing guarantees that it is not
> > > > +called before the stub gets to run. Thus, it needs to copy the final
> > > > +events table preboot size to the custom configuration table so that
> > > > +kernel offset it later on.
> 
>      (so that)
>      the kernel can use that final table preboot size as an events table
>      offset later on.
> 
> > > ?  kernel can offset it later on.
> > 
> > EFI stub calculates the total size of the events in the final events
> > table at the time.
> > 
> > Later on, TPM driver uses this offset to copy only the events that
> > were actually generated after ExitBootServices():
> > 
> > /*
> >  * Copy any of the final events log that didn't also end up in the
> >  * main log. Events can be logged in both if events are generated
> >  * between GetEventLog() and ExitBootServices().
> >  */
> > memcpy((void *)log->bios_event_log + log_size,
> >        final_tbl->events + log_tbl->final_events_preboot_size,
> >        efi_tpm_final_log_size);
> > 
> > What would be a better way to describe this?
> 
> Yeah, I think I see what it's doing, how it's using that.
> See above.
> 
> OK?

Your propsal looks legit, thank you. I'll send an update that
tries to address yours and Jordan's feedback.

/Jarkko