drm/i915: clarify reasoning for the access_ok call
This clarifies the comment above the access_ok check so a missing
VERIFY_READ doesn't alarm anyone.
v2:
- rewrote comment, thanks to Chris Wilson
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
[danvet: add patch history log to commit message.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 934396c..ea963c3 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -747,7 +747,11 @@
length = exec[i].relocation_count *
sizeof(struct drm_i915_gem_relocation_entry);
- /* we may also need to update the presumed offsets */
+ /*
+ * We must check that the entire relocation array is safe
+ * to read, but since we may need to update the presumed
+ * offsets during execution, check for full write access.
+ */
if (!access_ok(VERIFY_WRITE, ptr, length))
return -EFAULT;