Here is my first try for building an insecure kernel without su su or any other modifications.
Thanks to Androxyde for helping me build this kernel.
Xperia ION rooting pack: https://hotfile.com/dl/162186202/75d...oting.zip.html
Here is a batch file for adding su and busybox into the rom.
[Procedure for rooting]
1. Unlock the bootloader.
2. Flash your Xperia ION LT28i with the insecure kernel.
3. Boot the phone and connect with debugging on.
4. Extract the Xperia ION rooting pack and run the batch file.
5. Install the latest version of superuser and busybox from google play.