Everything is managed by OnStar through their device that's factory installed into every new Chevy vehicle. They have had security breaches and had to fix white-hat reported vulnerabilities in the past[1]. This system isn't just "4G wifi as a hotspot", it has almost full access to every system in the car.
Chevy offers this mobile app called MyLink which lets you remote-start, lock, unlock your car using this same connection.
History shows that car manufacturers have not given near enough thought to the security of access to a vehicle. I'm afraid that it's only a matter of time before we have a bot net either using cars, a bot-net that attacks and takes over cars, or both, with the potential of lots of damage and loss of life.
As such I immediately told OnStar to disable service to my car and will be finding and disconnecting the OnStar box (as it still phones home periodically) as I just have no reason to trust such a thing at this time.
[1] https://www.wired.com/2015/09/gm-took-5-years-fix-full-takeo...