Well - from some of the commentary on Wikipedia (I know it's not a great source, but...):
- Grsecurity distribute patches to the kernel, these are governed by GPLv2
- Grsecurity only sell these (not distribute for free), but as well as the GPLv2 license, they attach use conditions, basically saying "if you distribute these as per GPLv2 you don't get any future releases"
Grsecurity claim this means they're abiding by GPLv2, Perens says it breaks GPLv2. I suspect Perens is right, but the IP lawyers will have a bun fight over it in court.