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Message-ID: <0efe4ef1-30f5-47f8-b818-79b4cfa0891f@linaro.org>
Date: Mon, 23 Dec 2024 16:03:04 +0000
From: James Clark <james.clark@...aro.org>
To: Yeoreum Yun <yeoreum.yun@....com>, Mike Leach <mike.leach@...aro.org>
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org, nd@....com, suzuki.poulose@....com,
mike.leach@...aro.org, alexander.shishkin@...ux.intel.com
Subject: Re: [PATCH 1/1] coresight: prevent deactivate active config while
enable the config
On 18/12/2024 8:48 am, 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
> (perf or 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)
Assuming the left side does Perf, are there some steps missing? To get
to enable_active_config() you first need to pass through etm_setup_aux()
-> cscfg_activate_config(). That would also increment sys_active_cnt
which would leave it at 2 if there were two concurrent sessions. Then it
would end up as 1 here after deactivate, rather than 0.
It's not explicitly mentioned in the sequence but I'm assuming the left
and right are the same config, but I suppose it could be an issue with
different configs too.
> cscfg_unload_config_sets()
> unload module
On the left cscfg_activate_config() also bumps the module refcount, so
unload wouldn't cause a UAF here as far as I can see.
>
> // access to config_desc which freed
> // while unloading module.
> cfs_csdev_enable_config
>
> To address this, introduce sys_enable_cnt in cscfg_mgr to prevent
> deactivate while there is enabled configuration.
>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
> ---
> .../hwtracing/coresight/coresight-etm4x-core.c | 3 +++
> drivers/hwtracing/coresight/coresight-syscfg.c | 18 ++++++++++++++++--
> drivers/hwtracing/coresight/coresight-syscfg.h | 2 ++
> 3 files changed, 21 insertions(+), 2 deletions(-)
>
> 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..dfa7dcbaf25d 100644
> --- a/drivers/hwtracing/coresight/coresight-syscfg.c
> +++ b/drivers/hwtracing/coresight/coresight-syscfg.c
> @@ -953,7 +953,8 @@ int cscfg_config_sysfs_activate(struct cscfg_config_desc *config_desc, bool acti
> cscfg_mgr->sysfs_active_config = cfg_hash;
> } else {
> /* disable if matching current value */
> - if (cscfg_mgr->sysfs_active_config == cfg_hash) {
> + if (cscfg_mgr->sysfs_active_config == cfg_hash &&
> + !atomic_read(&cscfg_mgr->sys_enable_cnt)) {
> _cscfg_deactivate_config(cfg_hash);
So is sys_enable_cnt a global value? If a fix is needed doesn't it need
to be a per-config refcount?
Say you have two active configs, sys_enable_cnt is now 2, how do you
disable one without it always skipping here when the other config is
enabled?
> cscfg_mgr->sysfs_active_config = 0;
> } else
> @@ -1055,6 +1056,12 @@ int cscfg_csdev_enable_active_config(struct coresight_device *csdev,
> if (!atomic_read(&cscfg_mgr->sys_active_cnt))
> return 0;
>
> + /*
> + * increment sys_enable_cnt first to prevent deactivate the config
> + * while enable active config.
> + */
> + atomic_inc(&cscfg_mgr->sys_enable_cnt);
> +
> /*
> * Look for matching configuration - set the active configuration
> * context if found.
> @@ -1098,6 +1105,10 @@ int cscfg_csdev_enable_active_config(struct coresight_device *csdev,
> raw_spin_unlock_irqrestore(&csdev->cscfg_csdev_lock, flags);
> }
> }
> +
> + if (!config_csdev_active || err)
> + atomic_dec(&cscfg_mgr->sys_enable_cnt);
> +
> return err;
> }
> EXPORT_SYMBOL_GPL(cscfg_csdev_enable_active_config);
> @@ -1129,8 +1140,10 @@ void cscfg_csdev_disable_active_config(struct coresight_device *csdev)
> if (config_csdev) {
> if (!config_csdev->enabled)
> config_csdev = NULL;
> - else
> + else {
> config_csdev->enabled = false;
> + atomic_dec(&cscfg_mgr->sys_enable_cnt);
> + }
> }
> csdev->active_cscfg_ctxt = NULL;
> raw_spin_unlock_irqrestore(&csdev->cscfg_csdev_lock, flags);
> @@ -1179,6 +1192,7 @@ static int cscfg_create_device(void)
> INIT_LIST_HEAD(&cscfg_mgr->config_desc_list);
> INIT_LIST_HEAD(&cscfg_mgr->load_order_list);
> atomic_set(&cscfg_mgr->sys_active_cnt, 0);
> + atomic_set(&cscfg_mgr->sys_enable_cnt, 0);
> cscfg_mgr->load_state = CSCFG_NONE;
>
> /* setup the device */
> diff --git a/drivers/hwtracing/coresight/coresight-syscfg.h b/drivers/hwtracing/coresight/coresight-syscfg.h
> index 66e2db890d82..2fc397919985 100644
> --- a/drivers/hwtracing/coresight/coresight-syscfg.h
> +++ b/drivers/hwtracing/coresight/coresight-syscfg.h
> @@ -38,6 +38,7 @@ enum cscfg_load_ops {
> * @config_desc_list: List of system configuration descriptors to load into registered devices.
> * @load_order_list: Ordered list of owners for dynamically loaded configurations.
> * @sys_active_cnt: Total number of active config descriptor references.
> + * @sys_enable_cnt: Total number of enable of active config descriptor references.
When these are next to each other it makes me wonder why active_cnt
isn't enough to prevent unloading? Enabled is always a subset of active,
so as long as you gate unloads or modifications on the existing active
count it seems fine?
> * @cfgfs_subsys: configfs subsystem used to manage configurations.
> * @sysfs_active_config:Active config hash used if CoreSight controlled from sysfs.
> * @sysfs_active_preset:Active preset index used if CoreSight controlled from sysfs.
> @@ -50,6 +51,7 @@ struct cscfg_manager {
> struct list_head config_desc_list;
> struct list_head load_order_list;
> atomic_t sys_active_cnt;
> + atomic_t sys_enable_cnt;
> struct configfs_subsystem cfgfs_subsys;
> u32 sysfs_active_config;
> int sysfs_active_preset;
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