drm/i915/eb: Report EFAULT when writing updated exec_obj offset

This was thrown out in

commit 2889caa9232109afc8881f29a2205abeb5709d0c
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Fri Jun 16 15:05:19 2017 +0100

    drm/i915: Eliminate lots of iterations over the execobjects array

with the justification that we're already past the point of no return
(in a comment, not in the commit message).

That's true, but also if userspace is silly and hands us read-only
memory, then we'll only notice that when we write to it. So reporting
the error is still our duty, not that it's likely - at this point
we're dealing with nasty userspace anyway.

Also this is what we've been doing for around 8 years before this
patch changed it.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jon Bloomfield <jon.bloomfield@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Jason Ekstrand <jason@jlekstrand.net>

1 files changed, 5 insertions, 7 deletions

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 3753b9661f32..9f8c32c93d82 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -3590,16 +3590,11 @@ i915_gem_execbuffer2_ioctl(struct drm_device *dev, void *data,
 
 	err = i915_gem_do_execbuffer(dev, file, args, exec2_list);
 
-	/*
-	 * Now that we have begun execution of the batchbuffer, we ignore
-	 * any new error after this point. Also given that we have already
-	 * updated the associated relocations, we try to write out the current
-	 * object locations irrespective of any error.
-	 */
 	if (args->flags & __EXEC_HAS_RELOC) {
 		struct drm_i915_gem_exec_object2 __user *user_exec_list =
 			u64_to_user_ptr(args->buffers_ptr);
 		unsigned int i;
+		bool failed = true;
 
 		/* Copy the new buffer offsets back to the user's exec list. */
 		/*
@@ -3623,9 +3618,12 @@ i915_gem_execbuffer2_ioctl(struct drm_device *dev, void *data,
 					&user_exec_list[i].offset,
 					end_user);
 		}
+		failed = false;
 end_user:
 		user_write_access_end();
-end:;
+end:
+		if (failed)
+			err = -EFAULT;
 	}
 
 	args->flags &= ~__I915_EXEC_UNKNOWN_FLAGS;