[PATCH v4 1/2] tpm: Issue a TPM2_Shutdown for TPM2 devices.

[Josh Zimmerman <joshz@xxxxxxxxxx>]

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