[Intel-gfx] [PATCH v3 1/8] drm/i915: Make sure fb gtt offsets stay within 32bits

[Chris Wilson]

Quoting Ville Syrjala (2018-09-25 20:37:07)
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Let's try to make sure the fb offset computations never hit
> an integer overflow by making sure the entire fb stays
> below 32bits. framebuffer_check() in the core already does
> the same check, but as it doesn't know about tiling some things
> can slip through. Repeat the check in the driver with tiling
> taken into account.
> 
> v2: Use add_overflows() after massaging it to work for me (Chris)

Oh, it had fallen out of use.
 
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_utils.h    |  8 ++++----
>  drivers/gpu/drm/i915/intel_display.c | 18 +++++++++++++++++-
>  2 files changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
> index 395dd2511568..c43ec993fa90 100644
> --- a/drivers/gpu/drm/i915/i915_utils.h
> +++ b/drivers/gpu/drm/i915/i915_utils.h
> @@ -44,13 +44,13 @@
>                              __stringify(x), (long)(x))
>  
>  #if defined(GCC_VERSION) && GCC_VERSION >= 70000
> -#define add_overflows(A, B) \
> -       __builtin_add_overflow_p((A), (B), (typeof((A) + (B)))0)
> +#define add_overflows(A, B, C) \
> +       __builtin_add_overflow_p((A), (B), (C))
>  #else
> -#define add_overflows(A, B) ({ \
> +#define add_overflows(A, B, C) ({ \
>         typeof(A) a = (A); \
>         typeof(B) b = (B); \
> -       a + b < a; \
> +       (typeof(C))(a + b) < a; \
>  })
>  #endif
>  
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 4c5c2b39e65c..a3ae24e03316 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -2400,10 +2400,26 @@ static int intel_fb_offset_to_xy(int *x, int *y,
>                                  int color_plane)
>  {
>         struct drm_i915_private *dev_priv = to_i915(fb->dev);
> +       unsigned int height;
>  
>         if (fb->modifier != DRM_FORMAT_MOD_LINEAR &&
> -           fb->offsets[color_plane] % intel_tile_size(dev_priv))
> +           fb->offsets[color_plane] % intel_tile_size(dev_priv)) {
> +               DRM_DEBUG_KMS("Misaligned offset 0x%08x for color plane %d\n",
> +                             fb->offsets[color_plane], color_plane);
>                 return -EINVAL;
> +       }
> +
> +       height = drm_framebuffer_plane_height(fb->height, fb, color_plane);
> +       height = ALIGN(height, intel_tile_height(fb, color_plane));
> +
> +       /* Catch potential overflows early */
> +       if (add_overflows(mul_u32_u32(height, fb->pitches[color_plane]),
> +                         fb->offsets[color_plane], (u32)0)) {

Should we just pass type? Atm we aren't using the value for anything.
Then it would be add_overflows_t(a, b, T) with the obvious wrapping for
add_overflows(a, b). Although to be consistent with min_t, perhaps
add_overflows_t(T, a, b).
-Chris