linux-kernel - Re: tpm_tis TPM2.0 not detected on cold boot

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Date:   Sat, 29 Dec 2018 22:33:57 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Michael Niewöhner <linux@...ewoehner.de>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        peterhuewe@....de, jgg@...pe.ca, arnd@...db.de,
        linux-integrity@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Ken Goldman <kgold@...ux.ibm.com>
Subject: Re: tpm_tis TPM2.0 not detected on cold boot

On Tue, 2018-12-25 at 14:55 +0100, Michael Niewöhner wrote:
> On Sun, 2018-12-23 at 12:55 +0100, Michael Niewöhner wrote:
> > Hi Mimi,
> > 
> > On Sat, 2018-12-22 at 17:53 -0500, Mimi Zohar wrote:
> > > On Sat, 2018-12-22 at 14:47 +0100, Michael Niewöhner wrote:
> > > 
> > > > When I remove the timeout and boot directly to the linux kernel, I get
> > > > that
> > > > "2314 TPM-self test error" since it has not finished, yet. The TPM is
> > > > detected
> > > > by IMA and works fine then.
> > > > 
> > > > Some more tests showed that any delay before booting the kernel causes the
> > > > TPM
> > > > to not get detected. I tested, 10, 15, 20, 30, 60... seconds. Only in some
> > > > very
> > > > rare cases the TPM got detected.
> > > > 
> > > > I wanted to know if the TPM is in an well initialized state at the time of
> > > > that
> > > > error. Since I was not able to get some test/debug kernel patches working
> > > > I
> > > > decided to try kexec. It turned out that the TPM is indeed correctly
> > > > working
> > > > and
> > > > will be detected just fine by linux after kexec!
> > > 
> > > No surprise here.  kexec would be the equivalent of a soft reboot.
> > 
> > Well, I am not that deep in kexec internals but isn't a soft reboot much more
> > than a kexec? I thought kexec would "just" load the new kernel to memory and
> > executes it while a soft reboot goes at least through some UEFI
> > initialization.
> > For example, my pwm fans - in fact the EC - get resetted on a soft reboot,
> > while
> > a kexec does not touch them.
> > 

Similarly, the PCRs are not reset on kexec.

> > That is why I wanted to test if there is a different behaviour on kexec
> > compared
> > to a "real" soft reboot. If there was such difference I would have assumed a
> > UEFI bug that does not initialize the TPM correctly.
> > Kexec AFAIK does not invoke any UEFI initialization, so the TPM should be in
> > the
> > same state as before kexec and since there is no difference between sr and
> > kexec
> > I have the feeling there is something wrong in the kernel.
> > 
> > Correct me if I am wrong here, please.

But the problem you've described is on a cold boot, not a soft reboot.
 Both the soft reboot and kexec are working properly.  It seems the
difference is that on a cold boot, the TPM takes longer to initialize.

> > My current workaround is to do a machine_emergency_reboot() when TPM isn't
> > detected correctly. That is a pretty hard workaround but it seems to work for
> > now...

This is a again soft reboot.

>  
> > > 
> > > > 
> > > > Is there anyone having an idea what could be wrong here? I am willing to
> > > > debug
> > > > this but I have really no idea where to start :-(
> > > 
> > > A while ago, I was "playing" with a pi.  Commenting out
> > > tpm2_do_selftest() seemed to resolve a similar problem, but that was
> > > before James' patches.  I don't know if that would make a difference
> > > now.
> > 
> > Hm, I will try that..
> > 
> 
> Unfortunately this did not change anything

Not much I can do now.  After vacation, I'll set up the pi to see if
it is working properly with a recent kernel.

Mimi