arch/x86/entry/entry_64.S in the Linux kernel before 4.1.6 on the x86_64 platform does not properly determine when nested NMI processing is occurring, which allows local users to cause a denial of service (skipped NMI) by modifying the rsp register, issuing a syscall instruction, and triggering an NMI.
https://github.com/torvalds/linux/commit/810bc075f78ff2c221536eb3008eac6a492dba2d
https://bugzilla.redhat.com/show_bug.cgi?id=1243489
http://www.ubuntu.com/usn/USN-2691-1
http://www.ubuntu.com/usn/USN-2690-1
http://www.ubuntu.com/usn/USN-2689-1
http://www.ubuntu.com/usn/USN-2688-1
http://www.ubuntu.com/usn/USN-2687-1
http://www.securityfocus.com/bid/76003
http://www.openwall.com/lists/oss-security/2015/07/22/7
http://www.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.1.6