Re: [PATCH v5 3/3] coresight: prevent deactivate active config while enabling the config

[Leo Yan <leo.yan@arm.com>]

On Tue, May 13, 2025 at 06:06:22PM +0100, Yeoreum Yun 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.
> cscfg_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@arm.com>
> ---
>  .../hwtracing/coresight/coresight-config.h    |  2 +-
>  .../hwtracing/coresight/coresight-syscfg.c    | 49 +++++++++++++------
>  2 files changed, 35 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-syscfg.c b/drivers/hwtracing/coresight/coresight-syscfg.c
> index 5d194b9269f5..6d8c212ad434 100644
> --- a/drivers/hwtracing/coresight/coresight-syscfg.c
> +++ b/drivers/hwtracing/coresight/coresight-syscfg.c
> @@ -870,6 +870,25 @@ 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)

I would like to change the return type to int, so the error is handled
within the function.  As a result, the caller _cscfg_activate_config()
does not need to explicitly return an error value.

Otherwise, the patch looks good to me.

Thanks,
Leo

> +{
> +	if (!atomic_fetch_inc(&config_desc->active_cnt)) {
> +		/* must ensure that config cannot be unloaded in use */
> +		if (unlikely(cscfg_owner_get(config_desc->load_owner))) {
> +			atomic_dec(&config_desc->active_cnt);
> +			return false;
> +		}
> +	}
> +
> +	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.
> @@ -893,22 +912,17 @@ 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)) {
> +				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;
> @@ -923,9 +937,8 @@ 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;
>  		}
> @@ -1050,7 +1063,7 @@ 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;
>  
> @@ -1065,8 +1078,8 @@ 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)) {
>  			config_csdev_active = config_csdev_item;
>  			csdev->active_cscfg_ctxt = (void *)config_csdev_active;
>  			break;
> @@ -1100,7 +1113,11 @@ 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);
> @@ -1139,8 +1156,10 @@ 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}
>