Re: [PATCH v2] tpm: Issue a TPM2_Shutdown for TPM2 devices.

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Mon, May 15, 2017 at 10:33:04AM -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 (eventually, this
> will cause the TPM to 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.
> 
> This patch is dependent on '[PATCH] Add "shutdown" to "struct class".'
> http://marc.info/?l=linux-kernel&m=149463235025420&w=2
> 
> Signed-off-by: Josh Zimmerman <joshz-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> 
> v2:
>   - Properly split changes between this and another commit
>   - Use proper locking primitive.
>   - Fix commenting style
>  drivers/char/tpm/tpm-chip.c  | 20 ++++++++++++++++++++
>  drivers/char/tpm/tpm-sysfs.c |  2 ++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index 9dec9f551b83..e0c4323876b8 100644
> +++ 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

Single * for this comment

> +	 * 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.
> +	 */
> +	if (chip->flags & TPM_CHIP_FLAG_TPM2) {
> +		down_write(&chip->ops_sem);
> +		tpm2_shutdown(chip, TPM_SU_CLEAR);

Would it be appropriate to now chain to the device_driver shutdown
in case any TPM-bus related shutdown is required?

We don't have any drivers that need that today though.

>  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.

comment style again

Otherwise seems like a reasonable approach, we can fix the
TPM2-onlyness in later patches.

Jason

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