From: Omar Sandoval <osandov@osandov.com>
To: James Bottomley <James.Bottomley@hansenpartnership.com>
Cc: Peter Huewe <peterhuewe@gmx.de>,
Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
linux-integrity@vger.kernel.org
Subject: Re: [PATCH] tpm_tis: work around status register bug in STMicroelectronics TPM
Date: Wed, 15 Apr 2020 17:16:05 -0700 [thread overview]
Message-ID: <20200416001605.GA673482@vader> (raw)
In-Reply-To: <1586994699.3931.18.camel@HansenPartnership.com>
On Wed, Apr 15, 2020 at 04:51:39PM -0700, James Bottomley wrote:
> On Wed, 2020-04-15 at 15:45 -0700, Omar Sandoval wrote:
> > From: Omar Sandoval <osandov@fb.com>
> >
> > We've encountered a particular model of STMicroelectronics TPM that
> > transiently returns a bad value in the status register. This causes
> > the kernel to believe that the TPM is ready to receive a command when
> > it actually isn't, which in turn causes the send to time out in
> > get_burstcount(). In testing, reading the status register one extra
> > time convinces the TPM to return a valid value.
>
> Interesting, I've got a very early upgradeable nuvoton that seems to be
> behaving like this.
I'll attach the userspace reproducer I used to figure this out. I'd be
interested to see if it times out on your TPM, too. Note that it bangs
on /dev/mem and assumes that the MMIO address is 0xfed40000. That seems
to be the hard-coded address for x86 in the kernel, but just to be safe
you might want to check `grep MSFT0101 /proc/iomem`.
> > Signed-off-by: Omar Sandoval <osandov@fb.com>
> > ---
> > drivers/char/tpm/tpm_tis_core.c | 12 ++++++++++++
> > 1 file changed, 12 insertions(+)
> >
> > diff --git a/drivers/char/tpm/tpm_tis_core.c
> > b/drivers/char/tpm/tpm_tis_core.c
> > index 27c6ca031e23..277a21027fc7 100644
> > --- a/drivers/char/tpm/tpm_tis_core.c
> > +++ b/drivers/char/tpm/tpm_tis_core.c
> > @@ -238,6 +238,18 @@ static u8 tpm_tis_status(struct tpm_chip *chip)
> > rc = tpm_tis_read8(priv, TPM_STS(priv->locality), &status);
> > if (rc < 0)
> > return 0;
> > + /*
> > + * Some STMicroelectronics TPMs have a bug where the status
> > register is
> > + * sometimes bogus (all 1s) if read immediately after the
> > access
> > + * register is written to. Bits 0, 1, and 5 are always
> > supposed to read
> > + * as 0, so this is clearly invalid. Reading the register a
> > second time
> > + * returns a valid value.
> > + */
> > + if (unlikely(status == 0xff)) {
> > + rc = tpm_tis_read8(priv, TPM_STS(priv->locality),
> > &status);
> > + if (rc < 0)
> > + return 0;
> > + }
>
> You theorize that your case is fixed by the second read, but what if it
> isn't and the second read also returns 0xff? Shouldn't we have a line
> here saying
>
> if (unlikely(status == 0xff))
> status = 0;
>
> So if we get a second 0xff we just pretend the thing isn't ready?
We've been running this workaround in production for awhile and the
hangs haven't happened since, and my userspace reproducer never
witnessed a second 0xff. But it wouldn't hurt, so I can add it anyways.
next prev parent reply other threads:[~2020-04-16 0:16 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-15 22:45 [PATCH] tpm_tis: work around status register bug in STMicroelectronics TPM Omar Sandoval
2020-04-15 23:51 ` James Bottomley
2020-04-16 0:16 ` Omar Sandoval [this message]
2020-04-16 0:24 ` Omar Sandoval
2020-04-16 18:02 ` James Bottomley
2020-04-17 23:55 ` Jarkko Sakkinen
2020-04-18 0:12 ` James Bottomley
2020-04-20 20:46 ` Jarkko Sakkinen
2020-04-20 22:28 ` James Bottomley
2020-04-21 14:36 ` Mimi Zohar
2020-04-21 20:25 ` Jarkko Sakkinen
2020-04-21 20:31 ` Mimi Zohar
2020-04-21 20:23 ` Jarkko Sakkinen
2020-04-21 22:08 ` James Bottomley
2020-04-16 17:09 ` Jarkko Sakkinen
2020-04-16 17:56 ` James Bottomley
2020-08-27 15:24 ` Jason Andryuk
2020-08-28 23:18 ` Jarkko Sakkinen
2020-08-29 0:12 ` Jason Andryuk
2020-08-31 13:55 ` Jarkko Sakkinen
2020-09-04 12:03 ` Jarkko Sakkinen
2020-04-16 17:08 ` Jarkko Sakkinen
2020-04-16 18:54 ` Omar Sandoval
2020-04-17 23:54 ` Jarkko Sakkinen
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