The recent Communist Chinese missile knockout of their own satellite was at 500 miles altitude. The GPS satellites are 10,900 miles up, so there is immense amount of space between them. It would be much easier to jam them from a constellation of lower satellites transmitting on the same frequencies.
The low earth satellites presently in reach of Chinese missiles only provide a bit more precision, which is important in a CAT IIIb landing, but no big deal to a bomb.
Edit: Ooh, that was dumb; thanks, Gorrilla. I was thinking of WAAS, or whatever they call it now, which has nothing to do with CAT IIIb, at least not yet.
Beyond this, a Chinese ground based laser has blinded at least one of the US spy satellites. That makes it harder to monitor North Korea.
I am more concerned they would knock out the GEO satellites, killing my reception of Benny Hill reruns.
GB