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From: Peter Jones <pjones@redhat.com>
To: Tyler Hicks <tyhicks@linux.microsoft.com>
Cc: Ard Biesheuvel <ardb@kernel.org>,
	Matthew Garrett <mjg59@google.com>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	Peter Huewe <peterhuewe@gmx.de>, Jason Gunthorpe <jgg@ziepe.ca>,
	Petr Vandrovec <petr@vmware.com>,
	Nayna Jain <nayna@linux.ibm.com>,
	Thirupathaiah Annapureddy <thiruan@microsoft.com>,
	linux-integrity <linux-integrity@vger.kernel.org>,
	linux-efi <linux-efi@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] tpm: Require that all digests are present in TCG_PCR_EVENT2 structures
Date: Tue, 30 Jun 2020 15:48:56 -0400
Message-ID: <20200630194855.mfctxgveltvphgnc@redhat.com> (raw)
In-Reply-To: <20200630192322.GF4694@sequoia>

On Tue, Jun 30, 2020 at 02:23:22PM -0500, Tyler Hicks wrote:
> > > I am all for stringent checks, but this could potentially break
> > > measured boot on systems that are working fine today, right?
> > 
> > Seems like in that case our measurement is unreliable and can't really
> > be trusted.  That said, having things that were using the measurements
> > before this suddenly stop being able to access sealed secrets is not a
> > great experience for the user who unwittingly bought the junk hardware.
> 
> I haven't seen where anyone has suggested that such junk hardware
> exists. Do you know of or expect any firmware that has mismatched
> TCG_PCR_EVENT2.digests.count and TCG_EfiSpecIdEvent.numberOfAlgorithms
> values?

If nobody has seen any hardware that actually produces the values you're
excluding, then I don't have a strong objection.
 
> I would think that the userspace code that's parsing
> /sys/kernel/security/tpm0/binary_bios_measurements would also have
> issues with such an event log.
> 
> > Same with the zero-supported-hashes case.
> 
> Small but important correction: it is a zero-hashes case, not a
> zero-supported-hashes case
> 
> There's no handshake involved or anything like that. This would only
> cause problems if the firmware provided no hashes, which means the
> firmware event log is unusable, anyways.

Indeed.

-- 
        Peter


      reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-15 23:25 Tyler Hicks
2020-06-16  9:08 ` Ard Biesheuvel
2020-06-16 15:22   ` Tyler Hicks
2020-06-17 23:09   ` Jarkko Sakkinen
2020-06-30 18:33     ` Tyler Hicks
2020-07-02 23:57       ` Jarkko Sakkinen
2020-06-30 18:53   ` Peter Jones
2020-06-30 19:10     ` Ard Biesheuvel
2020-06-30 19:23     ` Tyler Hicks
2020-06-30 19:48       ` Peter Jones [this message]

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