Support for Control-flow Enforcement Technology (CET)?

My first question is, what Intel processors support CET?

As of October 20th 2017 there are no Intel processors currently being sold that support it.

Intel hasn't officially commented on when CET will be featured in new CPUs for control flow integrity protection, but given the timing of the GCC work, hopefully we'll see it in place for Cannonlake or worst case Ice lake.

Control-Flow Enforcement Technology Begins To Land In GCC 8

I performed a quick test using Fedora 26/GCC 7.2 on a 7th gen Core i5. It resulted in a failure, which was not surprising:

You need to use a version of GCC that supports this feature in order to use it within your program. This means you will want to use GCC 8.1 once it is released. It is unlikely kernel support will be required, but considering no processors on the market currently support, it is nearly impossible to predict what the requirements will be exactly.

However, I don't see any indication kernel support would be required, since these instructions that GCC would be using are platform independent. I would not be shocked if kernels added features, that used these instructions to their APIs in the future.