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@xxxxxxxxxxx>
Acked-by: William Breathitt Gray <vilhelm.gray@xxxxxxxxx>
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
>
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