Commit 4e26195f authored by Jason Gunthorpe's avatar Jason Gunthorpe Committed by Jarkko Sakkinen

tpm: Provide strong locking for device removal

Add a read/write semaphore around the ops function pointers so
ops can be set to null when the driver un-registers.

Previously the tpm core expected module locking to be enough to
ensure that tpm_unregister could not be called during certain times,
however that hasn't been sufficient for a long time.

Introduce a read/write semaphore around 'ops' so the core can set
it to null when unregistering. This provides a strong fence around
the driver callbacks, guaranteeing to the driver that no callbacks
are running or will run again.

For now the ops_lock is placed very high in the call stack, it could
be pushed down and made more granular in future if necessary.
Signed-off-by: default avatarJason Gunthorpe <jgunthorpe@obsidianresearch.com>
Reviewed-by: default avatarStefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: default avatarJarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: default avatarJarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
parent 3635e2ec
......@@ -36,10 +36,60 @@ static DEFINE_SPINLOCK(driver_lock);
struct class *tpm_class;
dev_t tpm_devt;
/*
* tpm_chip_find_get - return tpm_chip for a given chip number
* @chip_num the device number for the chip
/**
* 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 lock 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)
{
int rc = -EIO;
get_device(&chip->dev);
down_read(&chip->ops_sem);
if (!chip->ops)
goto out_lock;
if (!try_module_get(chip->dev.parent->driver->owner))
goto out_lock;
return 0;
out_lock:
up_read(&chip->ops_sem);
put_device(&chip->dev);
return rc;
}
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)
{
module_put(chip->dev.parent->driver->owner);
up_read(&chip->ops_sem);
put_device(&chip->dev);
}
EXPORT_SYMBOL_GPL(tpm_put_ops);
/**
* tpm_chip_find_get() - return tpm_chip for a given chip number
* @chip_num: id to find
*
* The return'd chip has been tpm_try_get_ops'd and must be released via
* tpm_put_ops
*/
struct tpm_chip *tpm_chip_find_get(int chip_num)
{
struct tpm_chip *pos, *chip = NULL;
......@@ -49,10 +99,10 @@ struct tpm_chip *tpm_chip_find_get(int chip_num)
if (chip_num != TPM_ANY_NUM && chip_num != pos->dev_num)
continue;
if (try_module_get(pos->dev.parent->driver->owner)) {
/* rcu prevents chip from being free'd */
if (!tpm_try_get_ops(pos))
chip = pos;
break;
}
break;
}
rcu_read_unlock();
return chip;
......@@ -95,6 +145,7 @@ struct tpm_chip *tpmm_chip_alloc(struct device *dev,
return ERR_PTR(-ENOMEM);
mutex_init(&chip->tpm_mutex);
init_rwsem(&chip->ops_sem);
INIT_LIST_HEAD(&chip->list);
chip->ops = ops;
......@@ -180,6 +231,12 @@ static int tpm_add_char_device(struct tpm_chip *chip)
static void tpm_del_char_device(struct tpm_chip *chip)
{
cdev_del(&chip->cdev);
/* Make the driver uncallable. */
down_write(&chip->ops_sem);
chip->ops = NULL;
up_write(&chip->ops_sem);
device_del(&chip->dev);
}
......@@ -265,6 +322,9 @@ EXPORT_SYMBOL_GPL(tpm_chip_register);
* Takes the chip first away from the list of available TPM chips and then
* cleans up all the resources reserved by tpm_chip_register().
*
* Once this function returns the driver call backs in 'op's will not be
* running and will no longer start.
*
* NOTE: This function should be only called before deinitializing chip
* resources.
*/
......
......@@ -136,9 +136,18 @@ static ssize_t tpm_write(struct file *file, const char __user *buf,
return -EFAULT;
}
/* atomic tpm command send and result receive */
/* atomic tpm command send and result receive. We only hold the ops
* 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)) {
mutex_unlock(&priv->buffer_mutex);
return -EPIPE;
}
out_size = tpm_transmit(priv->chip, priv->data_buffer,
sizeof(priv->data_buffer));
tpm_put_ops(priv->chip);
if (out_size < 0) {
mutex_unlock(&priv->buffer_mutex);
return out_size;
......
......@@ -700,7 +700,7 @@ int tpm_is_tpm2(u32 chip_num)
rc = (chip->flags & TPM_CHIP_FLAG_TPM2) != 0;
tpm_chip_put(chip);
tpm_put_ops(chip);
return rc;
}
......@@ -729,7 +729,7 @@ int tpm_pcr_read(u32 chip_num, int pcr_idx, u8 *res_buf)
rc = tpm2_pcr_read(chip, pcr_idx, res_buf);
else
rc = tpm_pcr_read_dev(chip, pcr_idx, res_buf);
tpm_chip_put(chip);
tpm_put_ops(chip);
return rc;
}
EXPORT_SYMBOL_GPL(tpm_pcr_read);
......@@ -764,7 +764,7 @@ int tpm_pcr_extend(u32 chip_num, int pcr_idx, const u8 *hash)
if (chip->flags & TPM_CHIP_FLAG_TPM2) {
rc = tpm2_pcr_extend(chip, pcr_idx, hash);
tpm_chip_put(chip);
tpm_put_ops(chip);
return rc;
}
......@@ -774,7 +774,7 @@ int tpm_pcr_extend(u32 chip_num, int pcr_idx, const u8 *hash)
rc = tpm_transmit_cmd(chip, &cmd, EXTEND_PCR_RESULT_SIZE,
"attempting extend a PCR value");
tpm_chip_put(chip);
tpm_put_ops(chip);
return rc;
}
EXPORT_SYMBOL_GPL(tpm_pcr_extend);
......@@ -855,7 +855,7 @@ int tpm_send(u32 chip_num, void *cmd, size_t buflen)
rc = tpm_transmit_cmd(chip, cmd, buflen, "attempting tpm_cmd");
tpm_chip_put(chip);
tpm_put_ops(chip);
return rc;
}
EXPORT_SYMBOL_GPL(tpm_send);
......@@ -1037,7 +1037,7 @@ int tpm_get_random(u32 chip_num, u8 *out, size_t max)
if (chip->flags & TPM_CHIP_FLAG_TPM2) {
err = tpm2_get_random(chip, out, max);
tpm_chip_put(chip);
tpm_put_ops(chip);
return err;
}
......@@ -1059,7 +1059,7 @@ int tpm_get_random(u32 chip_num, u8 *out, size_t max)
num_bytes -= recd;
} while (retries-- && total < max);
tpm_chip_put(chip);
tpm_put_ops(chip);
return total ? total : -EIO;
}
EXPORT_SYMBOL_GPL(tpm_get_random);
......@@ -1085,7 +1085,7 @@ int tpm_seal_trusted(u32 chip_num, struct trusted_key_payload *payload,
rc = tpm2_seal_trusted(chip, payload, options);
tpm_chip_put(chip);
tpm_put_ops(chip);
return rc;
}
EXPORT_SYMBOL_GPL(tpm_seal_trusted);
......@@ -1111,7 +1111,8 @@ int tpm_unseal_trusted(u32 chip_num, struct trusted_key_payload *payload,
rc = tpm2_unseal_trusted(chip, payload, options);
tpm_chip_put(chip);
tpm_put_ops(chip);
return rc;
}
EXPORT_SYMBOL_GPL(tpm_unseal_trusted);
......
......@@ -295,5 +295,10 @@ int tpm_sysfs_add_device(struct tpm_chip *chip)
void tpm_sysfs_del_device(struct tpm_chip *chip)
{
/* The sysfs routines rely on an implicit tpm_try_get_ops, this
* function is called before ops is null'd and the sysfs core
* synchronizes this removal so that no callbacks are running or can
* run again
*/
sysfs_remove_group(&chip->dev.parent->kobj, &tpm_dev_group);
}
......@@ -170,7 +170,13 @@ struct tpm_chip {
struct device dev;
struct cdev cdev;
/* A driver callback under ops cannot be run unless ops_sem is held
* (sometimes implicitly, eg for the sysfs code). ops becomes null
* when the driver is unregistered, see tpm_try_get_ops.
*/
struct rw_semaphore ops_sem;
const struct tpm_class_ops *ops;
unsigned int flags;
int dev_num; /* /dev/tpm# */
......@@ -195,11 +201,6 @@ struct tpm_chip {
#define to_tpm_chip(d) container_of(d, struct tpm_chip, dev)
static inline void tpm_chip_put(struct tpm_chip *chip)
{
module_put(chip->dev.parent->driver->owner);
}
static inline int tpm_read_index(int base, int index)
{
outb(index, base);
......@@ -507,6 +508,9 @@ extern int wait_for_tpm_stat(struct tpm_chip *, u8, unsigned long,
wait_queue_head_t *, bool);
struct tpm_chip *tpm_chip_find_get(int chip_num);
__must_check int tpm_try_get_ops(struct tpm_chip *chip);
void tpm_put_ops(struct tpm_chip *chip);
extern struct tpm_chip *tpmm_chip_alloc(struct device *dev,
const struct tpm_class_ops *ops);
extern int tpm_chip_register(struct tpm_chip *chip);
......
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