Re: [PATCH v11 2/9] coresight: etm3x: prohibit modifying cntr_val and reset while session is enabled

[Yeoreum Yun <yeoreum.yun@arm.com>]

On Tue, Sep 15, 2026 at 11:48:44AM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] coresight: TOCTOU race in sysfs configuration store functions
> --
> 
> commit 9a331a4cd5a9fd51e7380e92ed6bdd6d8e20d5e4
> Author: Yeoreum Yun <yeoreum.yun@arm.com>
> 
> coresight: etm3x: prohibit modifying cntr_val and reset while session is enabled
> 
> This commit attempts to prevent modifications to cntr_val and reset while
> a CoreSight trace session is enabled. It adds a check for the current
> mode using coresight_get_mode() before proceeding with the sysfs store
> operations.
> 
> > diff --git a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> > --- a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> > @@ -74,6 +74,8 @@ static ssize_t reset_store(struct device *dev,
> >  	ret = kstrtoul(buf, 16, &val);
> >  	if (ret)
> >  		return ret;
> > +	if (coresight_get_mode(drvdata->csdev))
> > +		return -EBUSY;
> >  
> >  	if (val) {
> >  		spin_lock(&drvdata->spinlock);
> 
> [Severity: Medium]
> Could this lockless check introduce a time-of-check to time-of-use race?
> 
> If a concurrent thread starts a trace session via the enable_source sysfs
> file right after coresight_get_mode() returns false, it might win the race
> before spin_lock() is acquired here.
> 
> This could result in resetting the configuration of an active trace session
> and erroneously releasing its trace ID, potentially leading to trace ID
> collisions and hardware trace stream corruption.
> 
> [ ... ]
> 
> > @@ -744,6 +746,8 @@ static ssize_t cntr_val_store(struct device *dev,
> >  	ret = kstrtoul(buf, 16, &val);
> >  	if (ret)
> >  		return ret;
> > +	if (coresight_get_mode(drvdata->csdev))
> > +		return -EBUSY;
> >  
> >  	spin_lock(&drvdata->spinlock);
> 
> [Severity: Medium]
> Is this susceptible to a similar race condition as reset_store?
> 
> Since coresight_get_mode() is checked outside the spinlock, a concurrent
> thread could enable the session just before spin_lock() is acquired,
> allowing the counter value to be modified while the session is active.

Anyway, the reset interface is nausty. but yeap it would be better to
check after grabbing *lock*  in here.

-- 
Sincerely,
Yeoreum Yun