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Message-ID: <CAJ9a7ViuVntYL62q=WYPkFR3++cyufPdKUHm0FUAPyGy76pB_A@mail.gmail.com>
Date: Fri, 14 Mar 2025 14:50:00 +0000
From: Mike Leach <mike.leach@...aro.org>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: suzuki.poulose@....com, james.clark@...aro.org,
alexander.shishkin@...ux.intel.com, coresight@...ts.linaro.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] coresight: prevent deactivate active config while
enabling the config
Hi,
On Thu, 9 Jan 2025 at 17:20, Yeoreum Yun <yeoreum.yun@....com> 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@....com>
> ---
> 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
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