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

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Message-ID: <a8ee93721a674434e22d31fd1d10bf9472c1c739.camel@linux.intel.com>
Date:   Fri, 05 Jul 2019 13:15:01 +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 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.
> 
> ?  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?

/Jarkko