[How To] repack XPERIA DRM-fix kernel.

[SXUsr]

Before attempting this you need to have a back up of your TA Partition and it's a MUST that you do that before unlocking your bootloader if you wish to retain your DRM keys, once they're gone they're gone!!

So if you haven't done that yet go do it now! - Universal (Dirtycow-based) TA Backup v2

Also note...

If you managed to backup for TA partition before then you can reactivate your original device key as follows:

flash_dk <ta backup image>  DK.ftf

Flashing this file with flashtool will write your device key to an alternative unit, from where the drmfix library will pick it up.
This is a one-time task. It will survive a complete reset of the phone or Android system upgrade. The device key has a length of just 16 bytes, so it is correct that the resulting DK.ftf has a size of only aprox. 500 bytes.

...to flash the DK.ftf you need to use Flashtool Version 9.22.3 for some reason, not sure if that still applies but if it doesn't work for you with the latest version you know where to get the one you need.

So begin by downloading and extracting these two tools, which can be used individually...

[PoC][Work in progress] Trim Area Proof Of Concept
[ROOT][Kernel][TWRP] repack of the stock kernel with dm-verity and SONY RIC off​

...I personally have one folder that I've called "Kernel Kit" and have both of these tools in it together as they don't conflict and just makes things easier. I did however copy PoC into the RootKernel folder as the only same file is the busybox application, pretty sure it's the same but PoC is newer so wanted to use that one, but it's up to you how you do it.

NOTE: You can add a recovery.img and your preferred SU to the folder/s. I prefer to flash TWRP to my recovery partition and flash SuperSU v2.82 and install Busybox after I've created my final kernel, but to include them in yours I believe you use PoC to include your recovery.img and Rootkernel to include your SU.zip and Busybox.​

Once your folder/s are set up you need to put your kernel.sin and TA.img in the PoC/Kernel Kit folder. I'm using the kernel.sin because it's the first format you come across when opening your .ftf with your favorite zip program, but PoC can use any format of kernel. So once you're at this stage we'll use the PoC tool first.

1. Click the DOUBLECLICKME file and you will be asked to select your kernel.sin and TA.img

2. When you get to the next step answer each of the following as follows...

dm-verity - y
Sony ric - y
Force-encypt - y for me but personal preference.​

...once it's done it will build a new_boot.img.

3. Open a cmd prompt window in the Rootkernel/Kernel Kit folder (alt + right click) then type/copy & paste the following...

rootkernel new_boot.img PoC_rk_194.img​

...(you can change PoC_rk_194.img to whatever name you want btw) and answer each of the following as follows...

Sony RIC - y
TWRP - n
DRM fix - n
Busybox - n​

...then once it's finished it will build a PoC_rk_194.img ready to be flashed to your phone.

Thanks to...

@rayman for Dirtycow
@munjeni for PoC
@tobias.waldvogel for Rootkernel​