arch/arm64/include/asm/pgtable.h in the Linux kernel before 3.15-rc5-next-20140519, as used in Android before 2016-07-05 on Nexus 5X and 6P devices, mishandles execute-only pages, which allows attackers to gain privileges via a crafted application, aka Android internal bug 28557020.
https://www.kernel.org/pub/linux/kernel/next/patch-v3.15-rc5-next-20140519.xz
https://github.com/torvalds/linux/commit/5a0fdfada3a2aa50d7b947a2e958bf00cbe0d830