Re: [PATCH v1 2/2] tpm: Issue a TPM2_Shutdown for TPM2 devices.

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Wed, Jul 12, 2017 at 05:41:21PM -0700, Josh Zimmerman wrote:
> Backport of d1bd4a792d3961a04e6154118816b00167aad91a upstream.
> 
> 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@google.com>

Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

/Jarkko


> ---
>  drivers/char/tpm/tpm-chip.c  | 36 ++++++++++++++++++++++++++++++++++++
>  drivers/char/tpm/tpm-sysfs.c |  5 +++++
>  2 files changed, 41 insertions(+)
> 
> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index a017ccd8cc3b..9ff853229957 100644
> --- a/drivers/char/tpm/tpm-chip.c
> +++ b/drivers/char/tpm/tpm-chip.c
> @@ -130,6 +130,41 @@ static void tpm_dev_release(struct device *dev)
>  	kfree(chip);
>  }
>  
> +
> +/**
> + * tpm_class_shutdown() - prepare the TPM device for loss of power.
> + * @dev: device to which the chip is associated.
> + *
> + * Issues a TPM2_Shutdown command prior to loss of power, as required by the
> + * TPM 2.0 spec.
> + * Then, calls bus- and device- specific shutdown code.
> + *
> + * XXX: This codepath relies on the fact that sysfs is not enabled for
> + * TPM2: sysfs uses an implicit lock on chip->ops, so this could race if TPM2
> + * has sysfs support enabled before TPM sysfs's implicit locking is fixed.
> + */
> +static int tpm_class_shutdown(struct device *dev)
> +{
> +	struct tpm_chip *chip = container_of(dev, struct tpm_chip, dev);
> +
> +	if (chip->flags & TPM_CHIP_FLAG_TPM2) {
> +		down_write(&chip->ops_sem);
> +		tpm2_shutdown(chip, TPM2_SU_CLEAR);
> +		chip->ops = NULL;
> +		up_write(&chip->ops_sem);
> +	}
> +	/* Allow bus- and device-specific code to run. Note: since chip->ops
> +	 * is NULL, more-specific shutdown code will not be able to issue TPM
> +	 * commands.
> +	 */
> +	if (dev->bus && dev->bus->shutdown)
> +		dev->bus->shutdown(dev);
> +	else if (dev->driver && dev->driver->shutdown)
> +		dev->driver->shutdown(dev);
> +	return 0;
> +}
> +
> +
>  /**
>   * tpm_chip_alloc() - allocate a new struct tpm_chip instance
>   * @pdev: device to which the chip is associated
> @@ -168,6 +203,7 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
>  	device_initialize(&chip->dev);
>  
>  	chip->dev.class = tpm_class;
> +	chip->dev.class->shutdown = tpm_class_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 a76ab4af9fb2..774148db0fac 100644
> --- a/drivers/char/tpm/tpm-sysfs.c
> +++ b/drivers/char/tpm/tpm-sysfs.c
> @@ -284,6 +284,11 @@ static const struct attribute_group tpm_dev_group = {
>  
>  void tpm_sysfs_add_device(struct tpm_chip *chip)
>  {
> +	/* XXX: If you wish to remove this restriction, you must first update
> +	 * tpm_sysfs to explicitly lock chip->ops.
> +	 */
> +	if (chip->flags & TPM_CHIP_FLAG_TPM2)
> +		return;
>  	/* The sysfs routines rely on an implicit tpm_try_get_ops, device_del
>  	 * is called before ops is null'd and the sysfs core synchronizes this
>  	 * removal so that no callbacks are running or can run again
> -- 
> 2.13.2.932.g7449e964c-goog
>