drm/i915: convert to using range_overflows

Convert some of the obvious hand-rolled ranged overflow sanity checks to
our shiny new range_overflows macro.

Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161213203222.32564-4-matthew.auld@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_gem.c

@@ -1140,8 +1140,7 @@ i915_gem_pread_ioctl(struct drm_device *dev, void *data,
 		return -ENOENT;
 
 	/* Bounds check source.  */
-	if (args->offset > obj->base.size ||
-	    args->size > obj->base.size - args->offset) {
+	if (range_overflows_t(u64, args->offset, args->size, obj->base.size)) {
 		ret = -EINVAL;
 		goto out;
 	}
@@ -1454,8 +1453,7 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
 		return -ENOENT;
 
 	/* Bounds check destination. */
-	if (args->offset > obj->base.size ||
-	    args->size > obj->base.size - args->offset) {
+	if (range_overflows_t(u64, args->offset, args->size, obj->base.size)) {
 		ret = -EINVAL;
 		goto err;
 	}

drivers/gpu/drm/i915/i915_vma.c

@@ -176,10 +176,9 @@ int i915_vma_bind(struct i915_vma *vma, enum i915_cache_level cache_level,
 	if (bind_flags == 0)
 		return 0;
 
-	if (GEM_WARN_ON(vma->node.start + vma->node.size < vma->node.start))
-		return -ENODEV;
-
-	if (GEM_WARN_ON(vma->node.start + vma->node.size > vma->vm->total))
+	if (GEM_WARN_ON(range_overflows(vma->node.start,
+					vma->node.size,
+					vma->vm->total)))
 		return -ENODEV;
 
 	if (vma_flags == 0 && vma->vm->allocate_va_range) {