From: Liam Beguin <liambeguin@gmail.com>
To: liambeguin@gmail.com, peda@axentia.se, jic23@kernel.org,
andy.shevchenko@gmail.com, lars@metafoo.de
Cc: linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org,
devicetree@vger.kernel.org, robh+dt@kernel.org
Subject: [PATCH v12 10/16] iio: afe: rescale: reduce risk of integer overflow
Date: Sat, 8 Jan 2022 15:53:13 -0500 [thread overview]
Message-ID: <20220108205319.2046348-11-liambeguin@gmail.com> (raw)
In-Reply-To: <20220108205319.2046348-1-liambeguin@gmail.com>
Reduce the risk of integer overflow by doing the scale calculation on
a 64-bit integer. Since the rescaling is only performed on *val, reuse
the IIO_VAL_FRACTIONAL_LOG2 case.
Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
---
drivers/iio/afe/iio-rescale.c | 23 ++++++++++++++++++-----
1 file changed, 18 insertions(+), 5 deletions(-)
diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index ed3ef994997f..5b87965482d2 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -24,21 +24,31 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
int *val, int *val2)
{
s64 tmp;
+ int _val, _val2;
s32 rem, rem2;
u32 mult;
u32 neg;
switch (scale_type) {
- case IIO_VAL_FRACTIONAL:
- *val *= rescale->numerator;
- *val2 *= rescale->denominator;
- return scale_type;
case IIO_VAL_INT:
*val *= rescale->numerator;
if (rescale->denominator == 1)
return scale_type;
*val2 = rescale->denominator;
return IIO_VAL_FRACTIONAL;
+ case IIO_VAL_FRACTIONAL:
+ /*
+ * When the product of both scales doesn't overflow, avoid
+ * potential accuracy loss (for in kernel consumers) by
+ * keeping a fractional representation.
+ */
+ if (!check_mul_overflow(*val, rescale->numerator, &_val) &&
+ !check_mul_overflow(*val2, rescale->denominator, &_val2)) {
+ *val = _val;
+ *val2 = _val2;
+ return IIO_VAL_FRACTIONAL;
+ }
+ fallthrough;
case IIO_VAL_FRACTIONAL_LOG2:
tmp = (s64)*val * 1000000000LL;
tmp = div_s64(tmp, rescale->denominator);
@@ -50,7 +60,10 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
if (!rem)
return scale_type;
- tmp = 1 << *val2;
+ if (scale_type == IIO_VAL_FRACTIONAL)
+ tmp = *val2;
+ else
+ tmp = ULL(1) << *val2;
rem2 = *val % (int)tmp;
*val = *val / (int)tmp;
--
2.34.0
next prev parent reply other threads:[~2022-01-08 20:54 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-08 20:53 [PATCH v12 00/16] iio: afe: add temperature rescaling support Liam Beguin
2022-01-08 20:53 ` [PATCH v12 01/16] iio: inkern: apply consumer scale on IIO_VAL_INT cases Liam Beguin
2022-01-08 20:53 ` [PATCH v12 02/16] iio: inkern: apply consumer scale when no channel scale is available Liam Beguin
2022-01-08 20:53 ` [PATCH v12 03/16] iio: inkern: make a best effort on offset calculation Liam Beguin
2022-01-08 20:53 ` [PATCH v12 04/16] iio: afe: rescale: use s64 for temporary scale calculations Liam Beguin
2022-01-08 20:53 ` [PATCH v12 05/16] iio: afe: rescale: reorder includes Liam Beguin
2022-01-08 20:53 ` [PATCH v12 06/16] iio: afe: rescale: expose scale processing function Liam Beguin
2022-01-09 13:07 ` Andy Shevchenko
2022-01-09 20:19 ` Peter Rosin
2022-01-09 20:25 ` Peter Rosin
2022-01-11 14:43 ` Liam Beguin
2022-01-11 14:35 ` Liam Beguin
2022-01-08 20:53 ` [PATCH v12 07/16] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support Liam Beguin
2022-01-09 12:48 ` Andy Shevchenko
2022-01-09 20:20 ` Peter Rosin
2022-01-11 14:33 ` Liam Beguin
2022-01-08 20:53 ` [PATCH v12 08/16] iio: afe: rescale: add offset support Liam Beguin
2022-01-08 20:53 ` [PATCH v12 09/16] iio: afe: rescale: fix accuracy for small fractional scales Liam Beguin
2022-01-09 13:02 ` Andy Shevchenko
2022-01-09 20:07 ` Peter Rosin
2022-01-08 20:53 ` Liam Beguin [this message]
2022-01-08 20:53 ` [PATCH v12 11/16] iio: afe: rescale: make use of units.h Liam Beguin
2022-01-08 20:53 ` [PATCH v12 12/16] iio: test: add basic tests for the iio-rescale driver Liam Beguin
2022-01-08 20:53 ` [PATCH v12 13/16] iio: afe: rescale: add RTD temperature sensor support Liam Beguin
2022-01-08 20:53 ` [PATCH v12 14/16] iio: afe: rescale: add temperature transducers Liam Beguin
2022-01-08 20:53 ` [PATCH v12 15/16] dt-bindings: iio: afe: add bindings for temperature-sense-rtd Liam Beguin
2022-01-08 20:53 ` [PATCH v12 16/16] dt-bindings: iio: afe: add bindings for temperature transducers Liam Beguin
2022-01-09 13:10 ` [PATCH v12 00/16] iio: afe: add temperature rescaling support Andy Shevchenko
2022-01-30 14:39 ` Jonathan Cameron
2022-01-30 14:41 ` Jonathan Cameron
2022-01-30 14:59 ` Liam Beguin
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