Re: [PATCH v4 1/2] tpm: Issue a TPM2_Shutdown for TPM2 devices.

[Jarkko Sakkinen <jarkko.sakkinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

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. 

> +       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.



> +
>  /**
>   * 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.

>         if (chip->flags & TPM_CHIP_FLAG_TPM2)
>                 return;
> 
> --
> 2.13.0.219.gdb65acc882-goog

/Jarkko

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