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Message-ID: <Z2msH5No7NAvFxcM@e129823.arm.com>
Date: Mon, 23 Dec 2024 18:29:51 +0000
From: Yeoreum Yun <yeoreum.yun@....com>
To: James Clark <james.clark@...aro.org>
Cc: Mike Leach <mike.leach@...aro.org>, coresight@...ts.linaro.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
nd@....com, suzuki.poulose@....com,
alexander.shishkin@...ux.intel.com
Subject: Re: [PATCH 1/1] coresight: prevent deactivate active config while
enable the config
Hi James.
>
>
> 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.
Sorry! This happens only in sysfs mode. not perf.
I've forgotten update the diagram...
>
> > 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.
>
In case of perf yes. However sysfs is done via configfs interface.
IOW, while cscfg_csdev_enable_active_config() iterating to find out the
config, it's possible to deactivate config via confis interface,
and unload moudle.
Above diagram explains this when coresight is configured with sysfs &
configfs interface NOT perf.
Sorry!
> >
> > // 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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