drm/i915/query: nospec expects no more than an unsigned long

nospec quite reasonably asserts that it will never be used with an index
larger than unsigned long (that being the largest possibly index into an
C array). However, our ubi uses the convention of u64 for any large
integer, running afoul of the assertion on 32b. Reduce our index to an
unsigned long, checking for type overflow first.

  drivers/gpu/drm/i915/i915_query.c: In function 'i915_query_ioctl':
  include/linux/compiler.h:339:38: error: call to '__compiletime_assert_119' declared with attribute error: BUILD_BUG_ON failed: sizeof(_s) > sizeof(long)

Reported-by: kbuild-all@01.org
Fixes: 84b510e2 ("drm/i915/query: Protect tainted function pointer lookup")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180522121018.15199-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_query.c

@@ -102,7 +102,7 @@ int i915_query_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
 
 	for (i = 0; i < args->num_items; i++, user_item_ptr++) {
 		struct drm_i915_query_item item;
-		u64 func_idx;
+		unsigned long func_idx;
 		int ret;
 
 		if (copy_from_user(&item, user_item_ptr, sizeof(item)))
@@ -111,6 +111,9 @@ int i915_query_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
 		if (item.query_id == 0)
 			return -EINVAL;
 
+		if (overflows_type(item.query_id - 1, unsigned long))
+			return -EINVAL;
+
 		func_idx = item.query_id - 1;
 
 		ret = -EINVAL;