On Tue, Sep 23, 2025 at 06:10:19PM +0100, Jonathan McDowell wrote: > 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_(try_get|put)_ops_locked, 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]>
Reviewed-by: Jarkko Sakkinen <[email protected]> > --- > v2: Switch to _locked instead of _internal_ for function names. > > 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 9c158c55c05f..c2ec56e2cd24 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 > I can take these to the next PR, thanks. BR, Jarkko
