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Message-ID: <20250514093900.GF26114@e132581.arm.com>
Date: Wed, 14 May 2025 10:39:00 +0100
From: Leo Yan <leo.yan@....com>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: mike.leach@...aro.org, 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 v5 3/3] coresight: prevent deactivate active config while
enabling the config
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@....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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