Re: [PATCH v3 1/1] coresight: prevent deactivate active config while enabling the config

[Mike Leach]

Hi,

On Thu, 9 Jan 2025 at 17:20, Yeoreum Yun <yeoreum.yun@xxxxxxx> wrote:
>
> While enable active config via cscfg_csdev_enable_active_config(),
> active config could be deactivated via configfs' sysfs interface.
> This could make UAF issue in below scenario:
>
> CPU0                                          CPU1
> (sysfs enable)                                load module
>                                               cscfg_load_config_sets()
>                                               activate config. // sysfs
>                                               (sys_active_cnt == 1)
> ...
> cscfg_csdev_enable_active_config()
>   lock(csdev->cscfg_csdev_lock)
>   // here load config activate by CPU1
>   unlock(csdev->cscfg_csdev_lock)
>
>                                               deactivate config // sysfs
>                                               (sys_activec_cnt == 0)
>                                               cscfg_unload_config_sets()
>                                               unload module
>
>   // access to config_desc which freed
>   // while unloading module.
>   cfs_csdev_enable_config
>
> To address this, use cscfg_config_desc's active_cnt as a reference count
> which will be holded when
>     - activate the config.
>     - enable the activated config.
> and put the module reference when config_active_cnt == 0.
>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>
> ---
> from v2 to v3:
>     - add cscfg_config_desc_get()/put() (from Suzuki).
>     - remove sys_enable_cnt.
>
> from v1 to v2:
>     - modify commit message.
> ---
>  .../hwtracing/coresight/coresight-config.h    |  2 +-
>  .../coresight/coresight-etm4x-core.c          |  3 +
>  .../hwtracing/coresight/coresight-syscfg.c    | 55 ++++++++++++++-----
>  3 files changed, 44 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-config.h b/drivers/hwtracing/coresight/coresight-config.h
> index b9ebc9fcfb7f..90fd937d3bd8 100644
> --- a/drivers/hwtracing/coresight/coresight-config.h
> +++ b/drivers/hwtracing/coresight/coresight-config.h
> @@ -228,7 +228,7 @@ struct cscfg_feature_csdev {
>   * @feats_csdev:references to the device features to enable.
>   */
>  struct cscfg_config_csdev {
> -       const struct cscfg_config_desc *config_desc;
> +       struct cscfg_config_desc *config_desc;
>         struct coresight_device *csdev;
>         bool enabled;
>         struct list_head node;
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index 86893115df17..6218ef40acbc 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -986,6 +986,9 @@ static void etm4_disable_sysfs(struct coresight_device *csdev)
>         smp_call_function_single(drvdata->cpu, etm4_disable_hw, drvdata, 1);
>
>         raw_spin_unlock(&drvdata->spinlock);
> +
> +       cscfg_csdev_disable_active_config(csdev);
> +
>         cpus_read_unlock();
>
>         /*
> diff --git a/drivers/hwtracing/coresight/coresight-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
> index a70c1454b410..8766f72db33e 100644
> --- a/drivers/hwtracing/coresight/coresight-syscfg.c
> +++ b/drivers/hwtracing/coresight/coresight-syscfg.c
> @@ -391,14 +391,17 @@ static void cscfg_owner_put(struct cscfg_load_owner_info *owner_info)
>  static void cscfg_remove_owned_csdev_configs(struct coresight_device *csdev, void *load_owner)
>  {
>         struct cscfg_config_csdev *config_csdev, *tmp;
> +       unsigned long flags;
>
>         if (list_empty(&csdev->config_csdev_list))
>                 return;
>
> +       raw_spin_lock_irqsave(&csdev->cscfg_csdev_lock, flags);
>         list_for_each_entry_safe(config_csdev, tmp, &csdev->config_csdev_list, node) {
>                 if (config_csdev->config_desc->load_owner == load_owner)
>                         list_del(&config_csdev->node);
>         }
> +       raw_spin_unlock_irqrestore(&csdev->cscfg_csdev_lock, flags);
>  }
>
>  static void cscfg_remove_owned_csdev_features(struct coresight_device *csdev, void *load_owner)
> @@ -867,6 +870,28 @@ void cscfg_csdev_reset_feats(struct coresight_device *csdev)
>  }
>  EXPORT_SYMBOL_GPL(cscfg_csdev_reset_feats);
>
> +static bool cscfg_config_desc_get(struct cscfg_config_desc *config_desc, bool enable)
> +{
> +       if (enable)
> +               return atomic_inc_not_zero(&config_desc->active_cnt);
> +

Not sure why we have an "enable" parameter here - it completely
changes the meaning of the function - with no comment at the start.

>From where it is called it makes figuring out the logic confusing.

Just keep the "get" functionality and drop the parameter & the nz check.

> +       /* when activate config */
> +
> +       /* must ensure that config cannot be unloaded in use */
> +       if (cscfg_owner_get(config_desc->load_owner))
> +               return false;
> +
> +       atomic_inc(&config_desc->active_cnt);
> +
> +       return true;
> +}
> +
> +static void cscfg_config_desc_put(struct cscfg_config_desc *config_desc)
> +{
> +       if (!atomic_dec_return(&config_desc->active_cnt))
> +               cscfg_owner_put(config_desc->load_owner);
> +}
> +
>  /*
>   * This activate configuration for either perf or sysfs. Perf can have multiple
>   * active configs, selected per event, sysfs is limited to one.
> @@ -890,22 +915,17 @@ static int _cscfg_activate_config(unsigned long cfg_hash)
>                         if (config_desc->available == false)
>                                 return -EBUSY;
>
> -                       /* must ensure that config cannot be unloaded in use */
> -                       err = cscfg_owner_get(config_desc->load_owner);
> -                       if (err)
> +                       if (!cscfg_config_desc_get(config_desc, false)) {

Drop the false parameter here.

> +                               err = -EINVAL;
>                                 break;
> +                       }
> +
>                         /*
>                          * increment the global active count - control changes to
>                          * active configurations
>                          */
>                         atomic_inc(&cscfg_mgr->sys_active_cnt);
>
> -                       /*
> -                        * mark the descriptor as active so enable config on a
> -                        * device instance will use it
> -                        */
> -                       atomic_inc(&config_desc->active_cnt);
> -
>                         err = 0;
>                         dev_dbg(cscfg_device(), "Activate config %s.\n", config_desc->name);
>                         break;
> @@ -920,9 +940,8 @@ static void _cscfg_deactivate_config(unsigned long cfg_hash)
>
>         list_for_each_entry(config_desc, &cscfg_mgr->config_desc_list, item) {
>                 if ((unsigned long)config_desc->event_ea->var == cfg_hash) {
> -                       atomic_dec(&config_desc->active_cnt);
>                         atomic_dec(&cscfg_mgr->sys_active_cnt);
> -                       cscfg_owner_put(config_desc->load_owner);
> +                       cscfg_config_desc_put(config_desc);
>                         dev_dbg(cscfg_device(), "Deactivate config %s.\n", config_desc->name);
>                         break;
>                 }
> @@ -1047,7 +1066,7 @@ int cscfg_csdev_enable_active_config(struct coresight_device *csdev,
>                                      unsigned long cfg_hash, int preset)
>  {
>         struct cscfg_config_csdev *config_csdev_active = NULL, *config_csdev_item;
> -       const struct cscfg_config_desc *config_desc;
> +       struct cscfg_config_desc *config_desc;
>         unsigned long flags;
>         int err = 0;
>
> @@ -1062,8 +1081,8 @@ int cscfg_csdev_enable_active_config(struct coresight_device *csdev,
>         raw_spin_lock_irqsave(&csdev->cscfg_csdev_lock, flags);
>         list_for_each_entry(config_csdev_item, &csdev->config_csdev_list, node) {
>                 config_desc = config_csdev_item->config_desc;
> -               if ((atomic_read(&config_desc->active_cnt)) &&
> -                   ((unsigned long)config_desc->event_ea->var == cfg_hash)) {
> +               if (((unsigned long)config_desc->event_ea->var == cfg_hash) &&
> +                               cscfg_config_desc_get(config_desc, true)) {

This obfuscates the logic of the comparisons without good reason. With
the true parameter, the function does no "get" operation but just
replicates the logic being replaced - checking the active_cnt is
non-zero.

Restore this to the original logic to make it readable again

Regards

Mike

>                         config_csdev_active = config_csdev_item;
>                         csdev->active_cscfg_ctxt = (void *)config_csdev_active;
>                         break;
> @@ -1097,7 +1116,11 @@ int cscfg_csdev_enable_active_config(struct coresight_device *csdev,
>                                 err = -EBUSY;
>                         raw_spin_unlock_irqrestore(&csdev->cscfg_csdev_lock, flags);
>                 }
> +
> +               if (err)
> +                       cscfg_config_desc_put(config_desc);
>         }
> +
>         return err;
>  }
>  EXPORT_SYMBOL_GPL(cscfg_csdev_enable_active_config);
> @@ -1136,8 +1159,10 @@ void cscfg_csdev_disable_active_config(struct coresight_device *csdev)
>         raw_spin_unlock_irqrestore(&csdev->cscfg_csdev_lock, flags);
>
>         /* true if there was an enabled active config */
> -       if (config_csdev)
> +       if (config_csdev) {
>                 cscfg_csdev_disable_config(config_csdev);
> +               cscfg_config_desc_put(config_csdev->config_desc);
> +       }
>  }
>  EXPORT_SYMBOL_GPL(cscfg_csdev_disable_active_config);
>
> --
> LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
>


-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK