RAP( Return address protection) is the most powerful kernel CFI implementation invented by PaX team and the 1st public version was released in PaX/Grsecurity 4.5.
* [Close, but No Cigar: On the Effectiveness of Intel's CET Against Code Reuse Attacks](https://grsecurity.net/effectiveness_of_intel_cet_against_code_reuse_attacks.php)