[PATCH 5.4 47/60] counter: stm32-timer-cnt: fix ceiling write max value

Greg Kroah-Hartman
2021-03-22T12:59:05Z

From: Fabrice Gasnier <fabrice.gasnier@foss.st.com>

commit e4c3e133294c0a292d21073899b05ebf530169bd upstream.

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.

[1] https://lkml.org/lkml/2021/2/12/358

Fixes: ad29937e206f ("counter: Add STM32 Timer quadrature encoder")
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Acked-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Cc: <Stable@vger.kernel.org>
Link: https://lore.kernel.org/r/1614696235-24088-1-git-send-email-fabrice.gasnier@foss.st.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/counter/stm32-timer-cnt.c | 5 +++++
1 file changed, 5 insertions(+)

--- a/drivers/counter/stm32-timer-cnt.c
+++ b/drivers/counter/stm32-timer-cnt.c
@@ -25,6 +25,7 @@ struct stm32_timer_cnt {
struct regmap *regmap;
struct clk *clk;
u32 ceiling;
+ u32 max_arr;
};

/**
@@ -189,6 +190,9 @@ static ssize_t stm32_count_ceiling_write
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);
@@ -366,6 +370,7 @@ static int stm32_timer_cnt_probe(struct
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;