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From: Josh Zimmerman <joshz-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
To: Jarkko Sakkinen
	<jarkko.sakkinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Cc: tpmdd-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
	jmorris-gx6/JNMH7DfYtjvyW6yDsg@public.gmane.org
Subject: Re: [PATCH v4 1/2] tpm: Issue a TPM2_Shutdown for TPM2 devices.
Date: Tue, 30 May 2017 12:00:53 -0700	[thread overview]
Message-ID: <CAHSjozABcEdQjpWQR3RV4B-cQ-Wfj_k7Bdr8pvG=CnD+RpU9zw@mail.gmail.com> (raw)
In-Reply-To: <20170530050701.drf6geqplnfezllv-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>

On Mon, May 29, 2017 at 10:07 PM, Jarkko Sakkinen
<jarkko.sakkinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> wrote:
> On Thu, May 25, 2017 at 04:20:28PM -0700, Josh Zimmerman wrote:
>> If a TPM2 loses power without a TPM2_Shutdown command being issued (a
>> "disorderly reboot"), it may lose some state that has yet to be
>> persisted to NVRam, and will increment the DA counter. After the DA
>> counter gets sufficiently large, the TPM will lock the user out.
>>
>> NOTE: This only changes behavior on TPM2 devices. Since TPM1 uses sysfs,
>> and sysfs relies on implicit locking on chip->ops, it is not safe to
>> allow this code to run in TPM1, or to add sysfs support to TPM2, until
>> that locking is made explicit.
>>
>> Signed-off-by: Josh Zimmerman <joshz-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
>> Reviewed-by: Jarko Sakkinen <jarkko.sakkinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
>> Cc: stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
>
> Still have some remarks.
>
>> ----
>> v2:
>>   - Properly split changes between this and another commit
>>   - Use proper locking primitive.
>>   - Fix commenting style
>> v3:
>>   - Re-fix commenting style
>> v4:
>>   - Update description and tags (Reviewed-by, Cc).
>> ---
>> ---
>>  drivers/char/tpm/tpm-chip.c  | 20 ++++++++++++++++++++
>>  drivers/char/tpm/tpm-sysfs.c |  3 +++
>>  2 files changed, 23 insertions(+)
>>
>> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
>> index 9dec9f551b83..272a42e77574 100644
>> --- a/drivers/char/tpm/tpm-chip.c
>> +++ b/drivers/char/tpm/tpm-chip.c
>> @@ -142,6 +142,25 @@ static void tpm_devs_release(struct device *dev)
>>         put_device(&chip->dev);
>>  }
>>
>> +static void tpm_shutdown(struct device *dev)
>> +{
>> +       struct tpm_chip *chip = container_of(dev, struct tpm_chip, dev);
>> +       /* TPM 2.0 requires that the TPM2_Shutdown() command be issued prior to
>> +        * loss of power. If it is not, the DA counter will be incremented and,
>> +        * eventually, the user will be locked out of their TPM.
>> +        * XXX: This codepath relies on the fact that sysfs is not enabled for
>> +        * TPM2: sysfs uses an implicit lock on chip->ops, so this use could
>> +        * race if TPM2 has sysfs support enabled before TPM sysfs's implicit
>> +        * locking is fixed.
>> +        */
>
> The comment should be either deleted or a kdoc.
Done.

>> +       if (chip->flags & TPM_CHIP_FLAG_TPM2) {
>> +               down_write(&chip->ops_sem);
>> +               tpm2_shutdown(chip, TPM_SU_CLEAR);
>> +               chip->ops = NULL;
>> +               up_write(&chip->ops_sem);
>> +       }
>> +}
>
> Would be a better idea to rename tpm2_shutdown as tpm_shutdown and call
> it unconditionally in tpm_del_char_device.
I'm not sure quite what you mean here. Are you suggesting that
tpm_del_char_device should unconditionally call the tpm_shutdown that
this patch introduces?  Or that the tpm2_shutdown function from
drivers/char/tpm/tpm2-cmd.c (which right now just sends the
TPM2_Shutdown command) be renamed to tpm_shutdown?

>> +
>>  /**
>>   * tpm_chip_alloc() - allocate a new struct tpm_chip instance
>>   * @pdev: device to which the chip is associated
>> @@ -181,6 +200,7 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
>>         device_initialize(&chip->devs);
>>
>>         chip->dev.class = tpm_class;
>> +       chip->dev.class.shutdown = tpm_shutdown;
>>         chip->dev.release = tpm_dev_release;
>>         chip->dev.parent = pdev;
>>         chip->dev.groups = chip->groups;
>> diff --git a/drivers/char/tpm/tpm-sysfs.c b/drivers/char/tpm/tpm-sysfs.c
>> index 55405dbe43fa..5e5ff7eb6f7e 100644
>> --- a/drivers/char/tpm/tpm-sysfs.c
>> +++ b/drivers/char/tpm/tpm-sysfs.c
>> @@ -294,6 +294,9 @@ static const struct attribute_group tpm_dev_group = {
>>
>>  void tpm_sysfs_add_device(struct tpm_chip *chip)
>>  {
>> +       /* XXX: Before this restriction is removed, tpm_sysfs must be updated
>> +        * to explicitly lock chip->ops.
>> +        */
>
> Not sure about this remark. Most, if not all, attributes in tpm-sysfs.c
> are useless attributes as you can use /dev/tpm0 to retrieve their
> values.
This is again in reference to
https://patchwork.kernel.org/patch/9516631/; if at some point in the
future a developer wishes to enable sysfs support for TPM2.0, the
implicit locking must be fixed.

I've attempted to clarify the phrasing here.

Josh

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  parent reply	other threads:[~2017-05-30 19:00 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-05-25 23:20 [PATCH v4 1/2] tpm: Issue a TPM2_Shutdown for TPM2 devices Josh Zimmerman
     [not found] ` <CAHSjozDnf5Nm9Nw=kKBQRRYYmEozT-m=XN-bxwLbk8Rs+=pduA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-05-30  5:07   ` Jarkko Sakkinen
     [not found]     ` <20170530050701.drf6geqplnfezllv-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-05-30 19:00       ` Josh Zimmerman [this message]
     [not found]         ` <CAHSjozABcEdQjpWQR3RV4B-cQ-Wfj_k7Bdr8pvG=CnD+RpU9zw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-05-31 12:01           ` Jarkko Sakkinen
     [not found]             ` <20170531120103.y6qf4v6hktzdbysx-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-05-31 22:08               ` Josh Zimmerman

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