linux-kernel - Re: [PATCH v4] tpm: Trigger only missing TPM 2.0 self tests

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Message-ID: <20180220225811.eedakhqvrmw3yhrb@linux.intel.com>
Date:   Wed, 21 Feb 2018 00:58:11 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     linux-integrity@...r.kernel.org
Cc:     linux-security-module@...r.kernel.org,
        Alexander Steffen <Alexander.Steffen@...ineon.com>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        Jarkko Sakkinen <jarkko.sakkine@...ux.intel.com>,
        Peter Huewe <peterhuewe@....de>,
        Jason Gunthorpe <jgg@...pe.ca>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] tpm: Trigger only missing TPM 2.0 self tests

On Wed, Feb 21, 2018 at 12:53:47AM +0200, Jarkko Sakkinen wrote:
> From: Alexander Steffen <Alexander.Steffen@...ineon.com>
> 
> My Nuvoton 6xx in a Dell XPS-13 has been intermittently failing to work
> (necessitating a reboot). The problem seems to be that the TPM gets into a
> state where the partial self-test doesn't return TPM_RC_SUCCESS (meaning
> all tests have run to completion), but instead returns TPM_RC_TESTING
> (meaning some tests are still running in the background).  There are
> various theories that resending the self-test command actually causes the
> tests to restart and thus triggers more TPM_RC_TESTING returns until the
> timeout is exceeded.
> 
> There are several issues here: firstly being we shouldn't slow down the
> boot sequence waiting for the self test to complete once the TPM
> backgrounds them.  It will actually make available all functions that have
> passed and if it gets a failure return TPM_RC_FAILURE to every subsequent
> command.  So the fix is to kick off self tests once and if they return
> TPM_RC_TESTING log that as a backgrounded self test and continue on.  In
> order to prevent other tpm users from seeing any TPM_RC_TESTING returns
> (which it might if they send a command that needs a TPM subsystem which is
> still under test), we loop in tpm_transmit_cmd until either a timeout or we
> don't get a TPM_RC_TESTING return.
> 
> Finally, there have been observations of strange returns from a partial
> test. One Nuvoton is occasionally returning TPM_RC_COMMAND_CODE, so treat
> any unexpected return from a partial self test as an indication we need to
> run a full self test.
> 
> Signed-off-by: Alexander Steffen <Alexander.Steffen@...ineon.com>
> Signed-off-by: James Bottomley <James.Bottomley@...senPartnership.com>
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkine@...ux.intel.com>
> Fixes: 2482b1bba5122b1d5516c909832bdd282015b8e9
> ---
> v4: Some updatees from jarkko.sakkinen@...ux.intel.com:
>     - squashed tpm_buf migration
>     - cleaned up a bunch of clutter from the original patch

I decided to rather just clean up the code. Would have taken more
time to explain than do the code change. Hope you don't mind and
hope I didn't break it.

/Jarkko