RE: TPM selftest failure in 4.15 (Dell XPS 13, Nuvoton 6xx)

Mario.Limonciello
2018-02-01T21:06:59Z

> -----Original Message-----
> From: Limonciello, Mario
> Sent: Thursday, February 1, 2018 2:12 PM
> To: 'Paul Menzel' <pmenzel@molgen.mpg.de>; James Bottomley
> <James.Bottomley@HansenPartnership.com>
> Cc: linux-integrity <linux-integrity@vger.kernel.org>; regressions@leemhuis.info;
> Alexander Steffen <Alexander.Steffen@infineon.com>
> Subject: RE: TPM selftest failure in 4.15 (Dell XPS 13, Nuvoton 6xx)
>
>
>
> > -----Original Message-----
> > From: Paul Menzel [mailto:pmenzel@molgen.mpg.de]
> > Sent: Thursday, February 1, 2018 1:17 PM
> > To: James Bottomley <James.Bottomley@HansenPartnership.com>
> > Cc: linux-integrity <linux-integrity@vger.kernel.org>; Limonciello, Mario
> > <Mario_Limonciello@Dell.com>; regressions@leemhuis.info; Alexander Steffen
> > <Alexander.Steffen@infineon.com>
> > Subject: Re: TPM selftest failure in 4.15 (Dell XPS 13, Nuvoton 6xx)
> >
> > [resend with regressions@ address fixed, sorry]
> >
> > Am 01.02.2018 um 20:16 schrieb Paul Menzel:
> > > Dear James,
> > >
> > >
> > > Am 01.02.2018 um 16:24 schrieb James Bottomley:
> > >> On Thu, 2018-02-01 at 12:42 +0000, James Bottomley wrote:
> > >>> On Thu, 2018-02-01 at 13:21 +0100, Paul Menzel wrote:
> > >
> > >>>> On 02/01/18 13:16, James Bottomley wrote:
> > >>>>>
> > >>>>>
> > >>>>> Embarrassingly enough, I'm just on my way to do a TPM talk at
> > >>>>> FOSDEM. I installed my shiny new 4.15 kernel on the 'plane and
> > >>>>> this is what I got after I arrived this morning:
> > >>>>>
> > >>>>> jejb@jarvis:~> dmesg | grep -i tpm
> > >>>>> [ 0.000000] ACPI: TPM2 0x0000000079446CC0 000034
> > >>>>> (v03 Tpm2Tabl 00000001 AMI 00000000)
> > >>>>> [ 1.598059] tpm_tis MSFT0101:00: 2.0 TPM (device-id 0xFE, rev-id 2)
> > >>>>> [ 1.608863] tpm tpm0: A TPM error (2314) occurred continue selftest
> > >>>>> [ 1.640052] tpm tpm0: A TPM error (2314) occurred continue selftest
> > >>>>> [ 1.691215] tpm tpm0: A TPM error (2314) occurred continue selftest
> > >>>>> [ 1.782377] tpm tpm0: A TPM error (2314) occurred continue selftest
> > >>>>> [ 1.953539] tpm tpm0: A TPM error (2314) occurred continue selftest
> > >>>>> [ 2.284701] tpm tpm0: A TPM error (2314) occurred continue selftest
> > >>>>> [ 2.935743] tpm tpm0: A TPM error (2314) occurred continue selftest
> > >>>>> [ 4.216236] tpm tpm0: TPM self test failed
> > >>>>> [ 4.236829] ima: No TPM chip found, activating TPM-bypass! (rc=-19)
> > >>>>>
> > >>>>> The error is TPM_RC_TESTING, which means it looks like we don't
> > >>>>> wait long enough for the selftests to complete. I get this all
> > >>>>> the time booting with 4.15. Fortunately I have a 4.13 backup
> > >>>>> kernel which is fine (otherwise I'd be a bit hosed since all my
> > >>>>> keys now require a TPM).
> > >>>>>
> > >>>>> I'll debug on the train; my current suspicion is that the
> > >>>>> TPM_LONG duration might be a bit short for this chip (A nuvoton
> > >>>>> 6xx in a dell XPS-13).
> > >>>>
> > >>>> Please join the thread [1], where I reported the same problem for
> > >>>> the Dell XPS 13 9360. Unfortunately, no solution was found,
> > >>>> especially, as I did not use the TPM. Other owners of that system
> > >>>> unfortunately didn't have time to report back if it work for them,
> > >>>> so the "conclusion" kind of was, that my TPM was broken, and had to
> > >>>> be tested.
> > >>>
> > >>> OK, I'll try to find a fix. It's clearly a marginal problem since
> > >>> I've booted most -rc kernels without issue, so there's some slight
> > >>> timing change in 4.15 that triggered it. It could also be a shutdown
> > >>> issue. Any NV ram stuff deferred to start up would take a variable
> > >>> amount of time.
> > >>>
> > >>> You'd almost think it's some sort of TPM self protest: the more stuff
> > >>> I use it for the more problems it seems to create. I'm definitely
> > >>> motivated to fix it because without a TPM I can't actually do much
> > >>> with my laptop.
> > >>
> > >> OK, I investigated but now my TPM has returned to normal (as in it
> > >> passes the selftest immediately). There's clearly something that makes
> > >> it return TPM_RC_TESTING to every self test probe for seconds at a
> > >> time, but I don't know what it is. Sending a different command seems
> > >> to cause the problem to clear (Managed to reproduce once with the patch
> > >> to verify), so this is my proposed fix. It's clearly nonsensical to
> > >> detach the driver because the self test still returns TPM_RC_TESTING,
> > >> so convert that return to a TPM_RC_SUCCESS on timeout. It prints a
> > >> warning message so we'll see it in the logs if it causes problems.
> > >> Given that this seems to be some type of internal TPM issue, I don't
> > >> believe changing the timings would work.
> > >
> > > Maybe Mario can confirm this issue too, now that Linux 4.15 is released.
> > > Maybe he also has a way to get the Nuvoton people involved.
>
> James,
>
> Did you actually experiment with changing the timings?
>
> I was told that TPMs that are FIPS validated (such as that in the XPS 13) may
> take longer for the self tests to run.
>
> > >
> > >> ---
> > >>
> > >> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> > >> index f40d20671a78..3e1b062d8888 100644
> > >> --- a/drivers/char/tpm/tpm2-cmd.c
> > >> +++ b/drivers/char/tpm/tpm2-cmd.c
> > >> @@ -872,6 +872,17 @@ static int tpm2_do_selftest(struct tpm_chip *chip)
> > >> /* wait longer the next round */
> > >> delay_msec *= 2;
> > >> }
> > >> + if (rc == TPM2_RC_TESTING) {
> > >> + /*
> > >> + * A return of RC_TESTING means the TPM is still
> > >> + * running self tests. If one fails it will go into
> > >> + * failure mode and return RC_FAILED to every command,
> > >> + * so treat a still in testing return as a success
> > >> + * rather than causing a driver detach.
> > >> + */
> > >> + dev_err(&chip->dev,"TPM: Still in testing mode after %dms,
> > >> continuing\n", delay_msec);
> > >> + rc = TPM2_RC_SUCCESS;
> > >> + }
> > >> return rc;
> > >> }
> > >

I discussed this with some folks and although it would fix the problem it is not
accurately characterizing the situation. What is likely happening here is that
issuing the self test command in succession is causing the TPM to restart the
self test and not complete. Instead the selfTestDone bit should be polled.

I feel Paul is right, if a solution can't be brought up to do this instead, this
commit 125a2210541079e8e7c69e629ad06cabed788f8c should be reverted.

> > > Alexander replied the following in the other thread. No idea if you read
> > > it yet.
> > >
> > >> The list of "A TPM error (2314) occurred continue selftest" is caused
> > >> by my commit 125a2210541079e8e7c69e629ad06cabed788f8c ("tpm: React
> > >> correctly to
> > >> RC_TESTING from TPM 2.0 self tests") [1]. 2314 is TPM_RC_TESTING, so
> > >> the TPM
> > >> tells us that self-tests are still running in the background. This
> > >> problem was
> > >> not visible in previous versions, since it (incorrectly) ignored >
> > >> TPM_RC_TESTING.
> > >
> > > Maybe the commit should be reverted for now until this has cleared up
> > > for the Dell XPS 13 9360(?) to adhere to Linux' no regression policy.
> > >
> > >
> > > Kind regards,
> > >
> > > Paul
> > >
> > >
> > > PS: Alexander will also be at FOSDEM and mentioned your talk [2].
> > >
> > >
> > > [1]
> > >
> >
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=125
> > a2210541079e8e7c69e629ad06cabed788f8[2]
> > > https://lists.01.org/pipermail/tpm2/2018-January/000486.html