[PATCH] drm/amd/display: perform a bounds check before filling dirty rectangles

[Hamza Mahfooz]

Currently, it is possible for us to access memory that we shouldn't.
Since, we acquire (possibly dangling) pointers to dirty rectangles
before doing a bounds check to make sure we can actually accommodate the
number of dirty rectangles userspace has requested to fill. This issue
is especially evident if a compositor requests both MPO and damage clips
at the same time, in which case I have observed a soft-hang. So, to
avoid this issue, perform the bounds check before filling a single dirty
rectangle and WARN() about it, if it is ever attempted in
fill_dc_dirty_rect().

Cc: sta...@vger.kernel.org # 6.1+
Fixes: 30ebe41582d1 ("drm/amd/display: add FB_DAMAGE_CLIPS support")
Signed-off-by: Hamza Mahfooz <hamza.mahf...@amd.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c 
b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 64b8dcf8dbda..66bb03d503ea 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -5065,11 +5065,7 @@ static inline void fill_dc_dirty_rect(struct drm_plane 
*plane,
                                      s32 y, s32 width, s32 height,
                                      int *i, bool ffu)
 {
-       if (*i > DC_MAX_DIRTY_RECTS)
-               return;
-
-       if (*i == DC_MAX_DIRTY_RECTS)
-               goto out;
+       WARN_ON(*i >= DC_MAX_DIRTY_RECTS);
 
        dirty_rect->x = x;
        dirty_rect->y = y;
@@ -5085,7 +5081,6 @@ static inline void fill_dc_dirty_rect(struct drm_plane 
*plane,
                        "[PLANE:%d] PSR SU dirty rect at (%d, %d) size (%d, 
%d)",
                        plane->base.id, x, y, width, height);
 
-out:
        (*i)++;
 }
 
@@ -5172,6 +5167,9 @@ static void fill_dc_dirty_rects(struct drm_plane *plane,
 
        *dirty_regions_changed = bb_changed;
 
+       if ((num_clips + (bb_changed ? 2 : 0)) > DC_MAX_DIRTY_RECTS)
+               goto ffu;
+
        if (bb_changed) {
                fill_dc_dirty_rect(new_plane_state->plane, &dirty_rects[i],
                                   new_plane_state->crtc_x,
@@ -5201,9 +5199,6 @@ static void fill_dc_dirty_rects(struct drm_plane *plane,
                                   new_plane_state->crtc_h, &i, false);
        }
 
-       if (i > DC_MAX_DIRTY_RECTS)
-               goto ffu;
-
        flip_addrs->dirty_rect_count = i;
        return;
 
-- 
2.40.1