Re: [PATCH] counter: stm32-timer-cnt: fix ceiling write max value

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 2 Mar 2021 23:56:46 +0900
William Breathitt Gray <vilhelm.gray@gmail.com> wrote:

> On Tue, Mar 02, 2021 at 03:43:55PM +0100, Fabrice Gasnier wrote:
> > The ceiling value isn't checked before writing it into registers. The user
> > could write a value higher than the counter resolution (e.g. 16 or 32 bits
> > indicated by max_arr). This makes most significant bits to be truncated.
> > Fix it by checking the max_arr to report a range error [1] to the user.
> > 
> > Fixes: ad29937e206f ("counter: Add STM32 Timer quadrature encoder")
> > 
> > [1] https://lkml.org/lkml/2021/2/12/358
> > 
> > Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>  
> 
> Acked-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Applied to the fixes-togreg branch of iio.git and marked for stable.

thanks

Jonathan
> 
> Side question: if priv->ceiling is tracking the current ceiling
> configuration, would it make sense to change stm32_count_ceiling_read()
> to print the value of priv->ceiling instead of doing a regmap_read()
> call?
> 
> > ---
> >  drivers/counter/stm32-timer-cnt.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/drivers/counter/stm32-timer-cnt.c b/drivers/counter/stm32-timer-cnt.c
> > index ef2a974..2cf0c05 100644
> > --- a/drivers/counter/stm32-timer-cnt.c
> > +++ b/drivers/counter/stm32-timer-cnt.c
> > @@ -32,6 +32,7 @@ struct stm32_timer_cnt {
> >  	struct regmap *regmap;
> >  	struct clk *clk;
> >  	u32 ceiling;
> > +	u32 max_arr;
> >  	bool enabled;
> >  	struct stm32_timer_regs bak;
> >  };
> > @@ -185,6 +186,9 @@ static ssize_t stm32_count_ceiling_write(struct counter_device *counter,
> >  	if (ret)
> >  		return ret;
> >  
> > +	if (ceiling > priv->max_arr)
> > +		return -ERANGE;
> > +
> >  	/* TIMx_ARR register shouldn't be buffered (ARPE=0) */
> >  	regmap_update_bits(priv->regmap, TIM_CR1, TIM_CR1_ARPE, 0);
> >  	regmap_write(priv->regmap, TIM_ARR, ceiling);
> > @@ -360,6 +364,7 @@ static int stm32_timer_cnt_probe(struct platform_device *pdev)
> >  	priv->regmap = ddata->regmap;
> >  	priv->clk = ddata->clk;
> >  	priv->ceiling = ddata->max_arr;
> > +	priv->max_arr = ddata->max_arr;
> >  
> >  	priv->counter.name = dev_name(dev);
> >  	priv->counter.parent = dev;
> > -- 
> > 2.7.4
> >