On Tue, May 30, 2017 at 12:00:53PM -0700, Josh Zimmerman wrote:
> On Mon, May 29, 2017 at 10:07 PM, Jarkko Sakkinen
> <jarkko.sakki...@linux.intel.com> wrote:
> > 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 <jo...@google.com>
> >> Reviewed-by: Jarko Sakkinen <jarkko.sakki...@linux.intel.com>
> >> Cc: sta...@vger.kernel.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.
> Done.
>
> >> + 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.
> I'm not sure quite what you mean here. Are you suggesting that
> tpm_del_char_device should unconditionally call the tpm_shutdown that
> this patch introduces? Or that the tpm2_shutdown function from
> drivers/char/tpm/tpm2-cmd.c (which right now just sends the
> TPM2_Shutdown command) be renamed to tpm_shutdown?
The second option. In addition can make that your patch set applies to
security/next so I can merge both. I realized that the first patch does
not apply so that needs a resend too.
> >> +
> >> /**
> >> * 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.
> This is again in reference to
> https://patchwork.kernel.org/patch/9516631/; if at some point in the
> future a developer wishes to enable sysfs support for TPM2.0, the
> implicit locking must be fixed.
>
> I've attempted to clarify the phrasing here.
>
> Josh
OK lets keep it!
/Jarkko
------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
tpmdd-devel mailing list
tpmdd-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/tpmdd-devel
