Re: [PATCH] drm/i915: use check_add_overflow() and drop local variants

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Fri, Apr 05, 2024 at 11:26:25PM +0300, Jani Nikula wrote:
> Prefer common check_add_overflow() from overflow.h over the locally
> rolled versions of it. While check_add_overflow() does require a
> variable to assign to, unlike add_overflows_t(), it's still better than
> having multiple versions around.
> 
> Cc: Kees Cook <keescook@chromium.org>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_fb.c |  6 +++---
>  drivers/gpu/drm/i915/i915_utils.h       | 14 --------------
>  2 files changed, 3 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_fb.c b/drivers/gpu/drm/i915/display/intel_fb.c
> index 3ea6470d6d92..86b443433e8b 100644
> --- a/drivers/gpu/drm/i915/display/intel_fb.c
> +++ b/drivers/gpu/drm/i915/display/intel_fb.c
> @@ -1106,7 +1106,7 @@ static int intel_fb_offset_to_xy(int *x, int *y,
>  {
>  	struct drm_i915_private *i915 = to_i915(fb->dev);
>  	unsigned int height;
> -	u32 alignment;
> +	u32 alignment, unused;
>  
>  	if (DISPLAY_VER(i915) >= 12 &&
>  	    !intel_fb_needs_pot_stride_remap(to_intel_framebuffer(fb)) &&
> @@ -1128,8 +1128,8 @@ static int intel_fb_offset_to_xy(int *x, int *y,
>  	height = ALIGN(height, intel_tile_height(fb, color_plane));
>  
>  	/* Catch potential overflows early */
> -	if (add_overflows_t(u32, mul_u32_u32(height, fb->pitches[color_plane]),
> -			    fb->offsets[color_plane])) {
> +	if (check_add_overflow(mul_u32_u32(height, fb->pitches[color_plane]),
> +			       fb->offsets[color_plane], &unused)) {
>  		drm_dbg_kms(&i915->drm,
>  			    "Bad offset 0x%08x or pitch %d for color plane %d\n",
>  			    fb->offsets[color_plane], fb->pitches[color_plane],
> diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
> index b45ef0560611..06ec6ceb61d5 100644
> --- a/drivers/gpu/drm/i915/i915_utils.h
> +++ b/drivers/gpu/drm/i915/i915_utils.h
> @@ -73,20 +73,6 @@ bool i915_error_injected(void);
>  	__i915_printk(i915, i915_error_injected() ? KERN_DEBUG : KERN_ERR, \
>  		      fmt, ##__VA_ARGS__)
>  
> -#if defined(GCC_VERSION) && GCC_VERSION >= 70000
> -#define add_overflows_t(T, A, B) \
> -	__builtin_add_overflow_p((A), (B), (T)0)
> -#else
> -#define add_overflows_t(T, A, B) ({ \
> -	typeof(A) a = (A); \
> -	typeof(B) b = (B); \
> -	(T)(a + b) < a; \
> -})
> -#endif
> -
> -#define add_overflows(A, B) \
> -	add_overflows_t(typeof((A) + (B)), (A), (B))
> -
>  #define range_overflows(start, size, max) ({ \
>  	typeof(start) start__ = (start); \
>  	typeof(size) size__ = (size); \
> -- 
> 2.39.2
>