The scale() functions detects invalid parameters, but continues
its calculations anyway. This causes bad results if negative values
are used for unsigned operations. Worst case, a division by 0 error
will be seen if source_min == source_max.
On top of that, after v6.13, the sequence of WARN_ON() followed by clamp()
may result in a build error with gcc 13.x.
drivers/gpu/drm/i915/display/intel_backlight.c: In function 'scale':
include/linux/compiler_types.h:542:45: error:
call to '__compiletime_assert_415' declared with attribute error:
clamp() low limit source_min greater than high limit source_max
This happens if the compiler decides to rearrange the code as follows.
if (source_min > source_max) {
WARN(..);
/* Do the clamp() knowing that source_min > source_max */
source_val = clamp(source_val, source_min, source_max);
} else {
/* Do the clamp knowing that source_min <= source_max */
source_val = clamp(source_val, source_min, source_max);
}
Fix the problem by evaluating the return values from WARN_ON and returning
immediately after a warning. While at it, fix divide by zero error seen
if source_min == source_max.
Analyzed-by: Linus Torvalds <torva...@linux-foundation.org>
Suggested-by: Linus Torvalds <torva...@linux-foundation.org>
Suggested-by: David Laight <david.laight.li...@gmail.com>
Cc: David Laight <david.laight.li...@gmail.com>
Cc: Jani Nikula <jani.nik...@linux.intel.com>
Cc: Andy Shevchenko <andriy.shevche...@linux.intel.com>
Signed-off-by: Guenter Roeck <li...@roeck-us.net>
---
v2: Simplify code to always return target_min after a warning,
and also warn if source_min == source_max.
drivers/gpu/drm/i915/display/intel_backlight.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/display/intel_backlight.c
b/drivers/gpu/drm/i915/display/intel_backlight.c
index 3f81a726cc7d..ca588bed82b9 100644
--- a/drivers/gpu/drm/i915/display/intel_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_backlight.c
@@ -40,8 +40,9 @@ static u32 scale(u32 source_val,
{
u64 target_val;
- WARN_ON(source_min > source_max);
- WARN_ON(target_min > target_max);
+ if (WARN_ON(source_min >= source_max) ||
+ WARN_ON(target_min > target_max))
+ return target_min;
/* defensive */
source_val = clamp(source_val, source_min, source_max);
--
2.45.2
