drm/i915/userptr: add user_size limit check

Don't allow a mismatch between obj->base.size/vma->size and the actual
number of pages for the backing store, which is limited to INT_MAX
pages.

v2: document what are missing before we can safely drop the limit check

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200117132413.1170563-1-matthew.auld@intel.com

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index e5558af..b64b0f3 100644 (file)
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -769,6 +769,23 @@ i915_gem_userptr_ioctl(struct drm_device *dev,
                            I915_USERPTR_UNSYNCHRONIZED))
                return -EINVAL;
 
+       /*
+        * XXX: There is a prevalence of the assumption that we fit the
+        * object's page count inside a 32bit _signed_ variable. Let's document
+        * this and catch if we ever need to fix it. In the meantime, if you do
+        * spot such a local variable, please consider fixing!
+        *
+        * Aside from our own locals (for which we have no excuse!):
+        * - sg_table embeds unsigned int for num_pages
+        * - get_user_pages*() mixed ints with longs
+        */
+
+       if (args->user_size >> PAGE_SHIFT > INT_MAX)
+               return -E2BIG;
+
+       if (overflows_type(args->user_size, obj->base.size))
+               return -E2BIG;
+
        if (!args->user_size)
                return -EINVAL;