On Mon, May 29, 2017 at 10:07 PM, Jarkko Sakkinen
<[email protected]> 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 <[email protected]>
>> Reviewed-by: Jarko Sakkinen <[email protected]>
>> Cc: [email protected]
>
> 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?
>> +
>> /**
>> * 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
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