Hi,
While browsing the source code and defconfig, I noticed the exynos-mem block device is enabled in the kernel you provide and is also word-writable.
It is the cause of the local root exploit published last month for Samsung phones, cf. http://forum.xda-developers.com/showthread.php?t=2048511
I'm no expert on Exynos SoC, but from what I gather, that block device is only used on android, so couldn't we at least disable it on ubuntu defconfig ?