How can I compile an Android kernel with root permission?

Question

I have successfully compiled an AOSP branch (andriod 5.1.1) and installed it to my nexus 5. I have also recompiled a new kernel and replaced the former kernel. I want to know if it is possible to gain root privilege by modify the kernel source code. If so, how?

Thanks!

Answer 1

in build/core/main.mk find block:

ifneq (,$(user_variant))
  # Target is secure in user builds.
  ADDITIONAL_DEFAULT_PROPERTIES += ro.secure=1

change ro.secure=0