On Thu, May 25, 2017 at 4:06 PM, Josh Zimmerman <joshz@xxxxxxxxxx> 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@xxxxxxxxxx>
> Reviewed-by: Jarko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
>
> ----
> 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.
> + */
> + 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);
> + }
> +}
> +
> /**
> * 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.
> + */
> if (chip->flags & TPM_CHIP_FLAG_TPM2)
> return;
>
> --
> 2.13.0.219.gdb65acc882-goog
>
This was not meant to be sent explicitly to stable@; git send-email
"helpfully" added stable@ to the emails cc's despite my --suppress-cc
argument. Apologies.
Josh