regmap: Disable debugfs when locking is disabled

The recently added support for disabling the regmap internal locking left
debugfs enabled for devices with the locking disabled. This is a problem
since debugfs allows userspace to do things like initiate reads from the
hardware which will use the scratch buffers protected by the regmap locking
so could cause data corruption.

For safety address this by just disabling debugfs for these devices. That
is overly conservative since some of the debugfs files just read internal
data structures but it's much simpler to implmement and less likely to
lead to problems with tooling that works with debugfs.

Reported-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

---

Compile tested only so far.

 drivers/base/regmap/internal.h       | 8 ++++++++
 drivers/base/regmap/regmap-debugfs.c | 3 +++
 drivers/base/regmap/regmap.c         | 1 +
 3 files changed, 12 insertions(+)

-- 
2.15.1

2017-12-12 18:13 GMT+01:00 Mark Brown <broonie@kernel.org>:
> The recently added support for disabling the regmap internal locking left

> debugfs enabled for devices with the locking disabled. This is a problem

> since debugfs allows userspace to do things like initiate reads from the

> hardware which will use the scratch buffers protected by the regmap locking

> so could cause data corruption.

>

> For safety address this by just disabling debugfs for these devices. That

> is overly conservative since some of the debugfs files just read internal

> data structures but it's much simpler to implmement and less likely to

> lead to problems with tooling that works with debugfs.

>

> Reported-by: Lars-Peter Clausen <lars@metafoo.de>

> Signed-off-by: Mark Brown <broonie@kernel.org>

> ---

>

> Compile tested only so far.

>

>  drivers/base/regmap/internal.h       | 8 ++++++++

>  drivers/base/regmap/regmap-debugfs.c | 3 +++

>  drivers/base/regmap/regmap.c         | 1 +

>  3 files changed, 12 insertions(+)

>

> diff --git a/drivers/base/regmap/internal.h b/drivers/base/regmap/internal.h

> index 8641183cac2f..8d652023f8bd 100644

> --- a/drivers/base/regmap/internal.h

> +++ b/drivers/base/regmap/internal.h

> @@ -77,6 +77,7 @@ struct regmap {

>         int async_ret;

>

>  #ifdef CONFIG_DEBUG_FS

> +       bool debugfs_disable;

>         struct dentry *debugfs;

>         const char *debugfs_name;

>

> @@ -215,10 +216,17 @@ struct regmap_field {

>  extern void regmap_debugfs_initcall(void);

>  extern void regmap_debugfs_init(struct regmap *map, const char *name);

>  extern void regmap_debugfs_exit(struct regmap *map);

> +

> +static void regmap_debugfs_disable(struct regmap *map)

> +{

> +       map->debugfs_disable = true;

> +}

> +

>  #else

>  static inline void regmap_debugfs_initcall(void) { }

>  static inline void regmap_debugfs_init(struct regmap *map, const char *name) { }

>  static inline void regmap_debugfs_exit(struct regmap *map) { }

> +static inline void regmap_debugfs_disable(struct regmap *map) { }

>  #endif

>

>  /* regcache core declarations */

> diff --git a/drivers/base/regmap/regmap-debugfs.c b/drivers/base/regmap/regmap-debugfs.c

> index 36ce3511c733..c8ecefd75d6f 100644

> --- a/drivers/base/regmap/regmap-debugfs.c

> +++ b/drivers/base/regmap/regmap-debugfs.c

> @@ -529,6 +529,9 @@ void regmap_debugfs_init(struct regmap *map, const char *name)

>         struct regmap_range_node *range_node;

>         const char *devname = "dummy";

>

> +       if (map->debugfs_disable)

> +               return;

> +


I would still add the dev_dbg() here like in my version, since someone
may start wondering why the debugfs files are not being creating for
certain regmaps.

Thanks,
Bartosz

>         /* If we don't have the debugfs root yet, postpone init */

>         if (!regmap_debugfs_root) {

>                 struct regmap_debugfs_node *node;

> diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c

> index 1da2a9fc40b0..b884da59dd71 100644

> --- a/drivers/base/regmap/regmap.c

> +++ b/drivers/base/regmap/regmap.c

> @@ -674,6 +674,7 @@ struct regmap *__regmap_init(struct device *dev,

>

>         if (config->disable_locking) {

>                 map->lock = map->unlock = regmap_lock_unlock_empty;

> +               regmap_debugfs_disable(map);

>         } else if (config->lock && config->unlock) {

>                 map->lock = config->lock;

>                 map->unlock = config->unlock;

> --

> 2.15.1

>

On Wed, Dec 13, 2017 at 04:50:20PM +0100, Bartosz Golaszewski wrote:

> I would still add the dev_dbg() here like in my version, since someone

> may start wondering why the debugfs files are not being creating for

> certain regmaps.


Sure, can you send a patch for that please - I already applied mine?

2017-12-13 17:47 GMT+01:00 Mark Brown <broonie@kernel.org>:
> On Wed, Dec 13, 2017 at 04:50:20PM +0100, Bartosz Golaszewski wrote:

>

>> I would still add the dev_dbg() here like in my version, since someone

>> may start wondering why the debugfs files are not being creating for

>> certain regmaps.

>

> Sure, can you send a patch for that please - I already applied mine?


Done.

Thanks,
Bartosz