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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Sep 25, 2018 at 09:29:44PM +0100, Chris Wilson wrote:
> Quoting Ville Syrjala (2018-09-25 20:37:07)
> > From: Ville Syrjälä <ville.syrjala@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@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).

Indeed, that does seem a bit more consistent with existing stuff.

-- 
Ville Syrjälä
Intel
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