coresight: prevent deactivate active config while enabling the config

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.

Fixes: f8cce2ff3c04 ("coresight: syscfg: Add API to activate and enable configurations")
Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20250514161951.3427590-4-yeoreum.yun@arm.com

diff --git a/drivers/hwtracing/coresight/coresight-config.h b/drivers/hwtracing/coresight/coresight-config.h
index b9ebc9fcfb7f204ad76d99801c5f752223addd5b..90fd937d3bd8376d7927c408e762f4dad0c9641a 100644 (file)
--- 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 23017612f2eae03c2146cf577257ced5e7d3c002..83dad24e0116d449e402f188dcab3b11ab4d0606 100644 (file)
--- a/drivers/hwtracing/coresight/coresight-syscfg.c
+++ b/drivers/hwtracing/coresight/coresight-syscfg.c
@@ -869,6 +869,25 @@ unlock_exit:
 }
 EXPORT_SYMBOL_GPL(cscfg_csdev_reset_feats);
 
+static bool cscfg_config_desc_get(struct cscfg_config_desc *config_desc)
+{
+       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.
@@ -892,22 +911,17 @@ 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;
@@ -922,9 +936,8 @@ 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;
                }
@@ -1049,7 +1062,7 @@ 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;
 
@@ -1064,8 +1077,8 @@ 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;
@@ -1099,7 +1112,11 @@ 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);
@@ -1138,8 +1155,10 @@ 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);