From $URL : Access to /dev/cpu/*/msr was protected only using filesystem checks. A local uid 0 (root) user with all capabilities dropped could use this flaw to execute arbitrary code in kernel mode. Upstream commit: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=c903f0456bc69176912dee6dd25c6a66ee1aed00 References: http://grsecurity.net/~spender/msr32.c
There are no longer any 2.x kernels available in the repository with the exception of sys-kernel/xbox-sources which is unsupported by security.