The RHEL kernel was missing some stack unwinder fixes which leads to an incorrect CS bit being set, and a kernel OOps. This can be triggered by an unprivileged local user on a EM64T architecture system. Note this doesn't affect upstream which contains a different fix. More details, fix, and reproducer in bz#213313 Marking private until update is released.
removing embargo
This issue has been addressed in following products: Red Hat Linux Enterprise 5 Via RHSA-2007:0940 available at https://rhn.redhat.com/errata/RHSA-2007-0940.html