The mm subsystem in the Linux kernel through 3.2 does not properly enforce the CONFIG_STRICT_DEVMEM protection mechanism, which allows local users to read or write to kernel memory locations in the first megabyte (and bypass slab-allocation access restrictions) via an application that opens the /dev/mem file, related to arch/x86/mm/init.c and drivers/char/mem.c.
https://usn.ubuntu.com/3583-2/
https://usn.ubuntu.com/3583-1/
https://github.com/torvalds/linux/commit/a4866aa812518ed1a37d8ea0c881dc946409de94
https://access.redhat.com/errata/RHSA-2018:1854
https://access.redhat.com/errata/RHSA-2017:2669
https://access.redhat.com/errata/RHSA-2017:2077
https://access.redhat.com/errata/RHSA-2017:1842
http://www.securityfocus.com/bid/97690
http://www.openwall.com/lists/oss-security/2017/04/16/4