drm/vmwgfx: Fix command defines and checks

Make sure all guest-backed object commands are properly packed.
Have the command verifier treat uninitialized command entries as invalid
rather than dereferencing NULL pointers.
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>

drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c

@@ -2032,6 +2032,9 @@ static int vmw_cmd_check(struct vmw_private *dev_priv,
 		goto out_invalid;
 
 	entry = &vmw_cmd_entries[cmd_id];
+	if (unlikely(!entry->func))
+		goto out_invalid;
+
 	if (unlikely(!entry->user_allow && !sw_context->kernel))
 		goto out_privileged;