linux-kernel - Re: [PATCH v6 07/14] x86: Secure Launch kernel early boot stub

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Date:   Tue, 16 May 2023 02:45:49 +0100
From:   Matthew Garrett <mjg59@...f.ucam.org>
To:     "Daniel P. Smith" <dpsmith@...rtussolutions.com>
Cc:     Ross Philipson <ross.philipson@...cle.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-integrity@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-crypto@...r.kernel.org, iommu@...ts.linux-foundation.org,
        kexec@...ts.infradead.org, linux-efi@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        ardb@...nel.org, James.Bottomley@...senpartnership.com,
        luto@...capital.net, nivedita@...m.mit.edu,
        kanth.ghatraju@...cle.com, trenchboot-devel@...glegroups.com
Subject: Re: [PATCH v6 07/14] x86: Secure Launch kernel early boot stub

On Mon, May 15, 2023 at 09:11:15PM -0400, Daniel P. Smith wrote:
> On 5/12/23 12:17, Ross Philipson wrote:
> > This is a good point. At this point it is really something we
> > overlooked. We will have to revisit this and figure out the best way to
> > find the final event log depending on how things booted.
> 
> I believe Ross misunderstood what you were asking for here. There are two
> reasons this is not possible or desired. The first reason is that on Intel,
> the DRTM log is not initialized by TrenchBoot code in the preamble. It is
> only responsible for allocating a buffer and recording the location in the
> TXT structures. When the SINIT ACM is executed, it will initialize the log
> and record the measurement that CPU sent directly to the TPM and then the
> measurements the ACM makes of the environment. If you pointed at the SRTM
> log, then the ACM would write over existing log, which I don't think you
> want. Now if you pointed at the tail end of the SRTM log, you would still
> end up with a second, separate log that just happens to be memory adjacent.

Ok. I think it would be clearer if either the function names or some 
comments expressly indicated that this refers to the DRTM event log and 
that that's a separate entity from the SRTM one, "event log" on its own 
is likely to cause people to think of the existing log rather than 
associate it with something else.