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

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Message-ID: <33ff21e2-1e27-cc85-0ea3-5127cb2598ba@linux.microsoft.com>
Date:   Sun, 7 Jul 2019 21:10:48 -0700
From:   Jordan Hand <jorhand@...ux.microsoft.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        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 7/5/19 3:26 AM, Jarkko Sakkinen wrote:
> On Wed, 2019-07-03 at 10:08 -0700, Jordan Hand 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.
>>
>> This doesn't really explain what the size will be used for. Matthew's
>> patch description for "tpm: Don't duplicate events from the final event
>> log in the TCG2 log" outlines this well. You could maybe word it
>> differently but I think the information is necessary:
>>
>> "We can avoid this problem by looking at the size of the Final Event Log
>> just before we call ExitBootServices() and exporting this to the main
>> kernel. The kernel can then skip over all events that occured before
>> ExitBootServices() and only append events that were not also logged to
>> the main log."
> 
> Not exactly sure what is missing from my paragraph. The way I see it has
> more information as it states what is used at as the vessel for
> exportation (the custom configuration table).
> 
> Maybe something like:
> 
> "Thus, it nees to save the final events table size at the time to the
> custom configuration table so that the TPM driver can later on skip the
> events generated during the preboot time."
> 
Yes, that sounds more clear to me.

Thanks,
Jordan