From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [PATCH v2] tpm: Issue a TPM2_Shutdown for TPM2 devices. Date: Mon, 15 May 2017 11:40:53 -0600 Message-ID: <20170515174053.GA6229@obsidianresearch.com> References: <20170515173304.12216-1-joshz@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20170515173304.12216-1-joshz-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: tpmdd-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Josh Zimmerman Cc: Greg Kroah-Hartman , tpmdd-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: tpmdd-devel@lists.sourceforge.net 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 > > 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 ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot