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

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

On Wed, May 14, 2025 at 10:30:19AM +0100, Leo Yan wrote:
> 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>

And please add a fix tag:

Fixes: f8cce2ff3c04 ("coresight: syscfg: Add API to activate and enable configurations")

> > ---
> >  .../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}
> > 
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