Re: Only a limited ban then
Most of the time, they would already have access to that information, because most secure facilities are already on maps. They may not say what they do in there, but that it's government property and you can't go in there is in most cases already known, and China already has a list of most of the people who work in such places as well as anyone who posted information about it online.
There are, of course, exceptions to that. However, those places tend to put a bit more into security than having a good lock, so people who work there are unlikely to be able to simply take their phone. There are some pieces of information that could be gleaned from a personal device, but the point of the law is to prevent the software from having access to data on the device, not metadata. Maybe they will try a more severe ban, as some of them have indicated a desire to do.