From: Jonathan McDowell <[email protected]> There are situations where userspace might reasonably desire exclusive access to the TPM, or the kernel's internal context saving + flushing may cause issues, for example when performing firmware upgrades. Extend the locking already used for avoiding concurrent userspace access to prevent internal users of the TPM when /dev/tpm<n> is in use.
The few internal users who already hold the open_lock are changed to use tpm_internal_(try_get|put)_ops, with the old tpm_(try_get|put)_ops functions changing to obtain read access to the open_lock. We return -EBUSY when another user has exclusive access, rather than adding waits. Signed-off-by: Jonathan McDowell <[email protected]> --- v2: Switch to _locked instead of _internal_ for function names. v3: Move to end of patch series. drivers/char/tpm/tpm-chip.c | 53 +++++++++++++++++++++++++------ drivers/char/tpm/tpm-dev-common.c | 8 ++--- drivers/char/tpm/tpm.h | 2 ++ drivers/char/tpm/tpm2-space.c | 5 ++- 4 files changed, 52 insertions(+), 16 deletions(-) diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c index ba906966721a..687f6d8cd601 100644 --- a/drivers/char/tpm/tpm-chip.c +++ b/drivers/char/tpm/tpm-chip.c @@ -144,7 +144,7 @@ void tpm_chip_stop(struct tpm_chip *chip) EXPORT_SYMBOL_GPL(tpm_chip_stop); /** - * tpm_try_get_ops() - Get a ref to the tpm_chip + * tpm_try_get_ops_locked() - Get a ref to the tpm_chip * @chip: Chip to ref * * The caller must already have some kind of locking to ensure that chip is @@ -154,7 +154,7 @@ EXPORT_SYMBOL_GPL(tpm_chip_stop); * * Returns -ERRNO if the chip could not be got. */ -int tpm_try_get_ops(struct tpm_chip *chip) +int tpm_try_get_ops_locked(struct tpm_chip *chip) { int rc = -EIO; @@ -185,22 +185,57 @@ int tpm_try_get_ops(struct tpm_chip *chip) put_device(&chip->dev); return rc; } -EXPORT_SYMBOL_GPL(tpm_try_get_ops); /** - * tpm_put_ops() - Release a ref to the tpm_chip + * tpm_put_ops_locked() - Release a ref to the tpm_chip * @chip: Chip to put * - * This is the opposite pair to tpm_try_get_ops(). After this returns chip may - * be kfree'd. + * This is the opposite pair to tpm_try_get_ops_locked(). After this returns + * chip may be kfree'd. */ -void tpm_put_ops(struct tpm_chip *chip) +void tpm_put_ops_locked(struct tpm_chip *chip) { tpm_chip_stop(chip); mutex_unlock(&chip->tpm_mutex); up_read(&chip->ops_sem); put_device(&chip->dev); } + +/** + * tpm_try_get_ops() - Get a ref to the tpm_chip + * @chip: Chip to ref + * + * The caller must already have some kind of locking to ensure that chip is + * valid. This function will attempt to get the open_lock for the chip, + * ensuring no other user is expecting exclusive access, before locking the + * chip so that the ops member can be accessed safely. The locking prevents + * tpm_chip_unregister from completing, so it should not be held for long + * periods. + * + * Returns -ERRNO if the chip could not be got. + */ +int tpm_try_get_ops(struct tpm_chip *chip) +{ + if (!down_read_trylock(&chip->open_lock)) + return -EBUSY; + + return tpm_try_get_ops_locked(chip); +} +EXPORT_SYMBOL_GPL(tpm_try_get_ops); + +/** + * tpm_put_ops() - Release a ref to the tpm_chip + * @chip: Chip to put + * + * This is the opposite pair to tpm_try_get_ops(). After this returns + * chip may be kfree'd. + */ +void tpm_put_ops(struct tpm_chip *chip) +{ + tpm_put_ops_locked(chip); + + up_read(&chip->open_lock); +} EXPORT_SYMBOL_GPL(tpm_put_ops); /** @@ -644,10 +679,10 @@ void tpm_chip_unregister(struct tpm_chip *chip) #ifdef CONFIG_TCG_TPM2_HMAC int rc; - rc = tpm_try_get_ops(chip); + rc = tpm_try_get_ops_locked(chip); if (!rc) { tpm2_end_auth_session(chip); - tpm_put_ops(chip); + tpm_put_ops_locked(chip); } #endif diff --git a/drivers/char/tpm/tpm-dev-common.c b/drivers/char/tpm/tpm-dev-common.c index f2a5e09257dd..0f5bc63411aa 100644 --- a/drivers/char/tpm/tpm-dev-common.c +++ b/drivers/char/tpm/tpm-dev-common.c @@ -65,7 +65,7 @@ static void tpm_dev_async_work(struct work_struct *work) mutex_lock(&priv->buffer_mutex); priv->command_enqueued = false; - ret = tpm_try_get_ops(priv->chip); + ret = tpm_try_get_ops_locked(priv->chip); if (ret) { priv->response_length = ret; goto out; @@ -73,7 +73,7 @@ static void tpm_dev_async_work(struct work_struct *work) ret = tpm_dev_transmit(priv->chip, priv->space, priv->data_buffer, sizeof(priv->data_buffer)); - tpm_put_ops(priv->chip); + tpm_put_ops_locked(priv->chip); /* * If ret is > 0 then tpm_dev_transmit returned the size of the @@ -220,14 +220,14 @@ ssize_t tpm_common_write(struct file *file, const char __user *buf, * lock during this period so that the tpm can be unregistered even if * the char dev is held open. */ - if (tpm_try_get_ops(priv->chip)) { + if (tpm_try_get_ops_locked(priv->chip)) { ret = -EPIPE; goto out; } ret = tpm_dev_transmit(priv->chip, priv->space, priv->data_buffer, sizeof(priv->data_buffer)); - tpm_put_ops(priv->chip); + tpm_put_ops_locked(priv->chip); if (ret > 0) { priv->response_length = ret; diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h index 02c07fef41ba..57ef8589f5f5 100644 --- a/drivers/char/tpm/tpm.h +++ b/drivers/char/tpm/tpm.h @@ -272,6 +272,8 @@ struct tpm_chip *tpm_chip_alloc(struct device *dev, const struct tpm_class_ops *ops); struct tpm_chip *tpmm_chip_alloc(struct device *pdev, const struct tpm_class_ops *ops); +int tpm_try_get_ops_locked(struct tpm_chip *chip); +void tpm_put_ops_locked(struct tpm_chip *chip); int tpm_chip_register(struct tpm_chip *chip); void tpm_chip_unregister(struct tpm_chip *chip); diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c index 60354cd53b5c..0ad5e18355e0 100644 --- a/drivers/char/tpm/tpm2-space.c +++ b/drivers/char/tpm/tpm2-space.c @@ -58,10 +58,9 @@ int tpm2_init_space(struct tpm_space *space, unsigned int buf_size) void tpm2_del_space(struct tpm_chip *chip, struct tpm_space *space) { - - if (tpm_try_get_ops(chip) == 0) { + if (tpm_try_get_ops_locked(chip) == 0) { tpm2_flush_sessions(chip, space); - tpm_put_ops(chip); + tpm_put_ops_locked(chip); } kfree(space->context_buf); -- 2.51.0
