FreeBSD Security Advisory – If a General Protection Fault happens on a FreeBSD/amd64 system while it is returning from an interrupt, trap or system call, the swapgs CPU instruction may be called one extra time when it should not resulting in userland and kernel state being mixed. A local attacker can by causing a General Protection Fault while the kernel is returning from an interrupt, trap or system call while manipulating stack frames and, run arbitrary code with kernel privileges.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/69617/FreeBSD-SA-08-07.amd64.txt
Source: https://packetstormsecurity.com/files/69617/FreeBSD-SA-08-07.amd64.txt.html