[Intel-gfx] [PATCH v4 1/8] drm/i915: Make sure fb gtt offsets stay within 32bits

[Chris Wilson]

Quoting Ville Syrjala (2018-10-23 17:02:01)
> 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)
> v3: Call it add_overflow_t() to match min_t() & co. (Chris)
> 
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_utils.h    | 11 +++++++----
>  drivers/gpu/drm/i915/intel_display.c | 18 +++++++++++++++++-
>  2 files changed, 24 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
> index 5858a43e19da..9726df37c4c4 100644
> --- a/drivers/gpu/drm/i915/i915_utils.h
> +++ b/drivers/gpu/drm/i915/i915_utils.h
> @@ -44,16 +44,19 @@
>                              __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_t(T, A, B) \
> +       __builtin_add_overflow_p((A), (B), (T)0)
>  #else
> -#define add_overflows(A, B) ({ \
> +#define add_overflows_t(T, A, B) ({ \
>         typeof(A) a = (A); \
>         typeof(B) b = (B); \
> -       a + b < a; \
> +       (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); \
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 969d22ca8dcd..e520facc23e1 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -2351,10 +2351,26 @@ 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));

fb height is limited to u16 or thereabouts?

> +
> +       /* Catch potential overflows early */
> +       if (add_overflows_t(u32, mul_u32_u32(height, fb->pitches[color_plane]),
> +                           fb->offsets[color_plane])) {
> +               DRM_DEBUG_KMS("Bad offset 0x%08x or pitch %d for color plane %d\n",
> +                             fb->offsets[color_plane], fb->pitches[color_plane],
> +                             color_plane);
> +               return -ERANGE;
> +       }

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris