From a333c5c524c4e00183a34f93b075235ebf7d3325 Mon Sep 17 00:00:00 2001 From: Guenter Roeck Date: Tue, 21 Jan 2025 06:52:03 -0800 Subject: [PATCH] drm/i915/backlight: Return immediately when scale() finds invalid parameters commit 6f71507415841d1a6d38118e5fa0eaf0caab9c17 upstream. 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 Suggested-by: Linus Torvalds Suggested-by: David Laight Cc: David Laight Cc: Jani Nikula Cc: Andy Shevchenko Signed-off-by: Guenter Roeck Reviewed-by: Rodrigo Vivi Link: https://patchwork.freedesktop.org/patch/msgid/20250121145203.2851237-1-linux@roeck-us.net Signed-off-by: Rodrigo Vivi Signed-off-by: Greg Kroah-Hartman --- 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 beba39a38c87..6d69e75a287c 100644 --- a/drivers/gpu/drm/i915/display/intel_backlight.c +++ b/drivers/gpu/drm/i915/display/intel_backlight.c @@ -39,8 +39,9 @@ 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);