The ptrace_setxregs function in arch/xtensa/kernel/ptrace.c in the Linux kernel before 3.1 does not validate user-space pointers, which allows local users to obtain sensitive information from kernel memory locations via a crafted PTRACE_SETXTREGS request.
https://github.com/torvalds/linux/commit/0d0138ebe24b94065580bd2601f8bb7eb6152f56
http://www.openwall.com/lists/oss-security/2011/07/20/18