[Samsung Galaxy S8 & S8+ Cross Device Development] dr.ketan:
ROOT(Magisk) + OEM Fix + Busybox + EFS Backup

Pie

1.Enable Developer Option (settings - about phone - Software information - Tap 7 times on build number to activate developer option in settings menu)

2.Enable OEM Unlock from developer option

3.Download and copy Pie_G955F_Root_for_OEM_issue_devices_V*.zip to Ext SD card

4.Download TWRP for S8 from official page https://twrp.me

5.Switch Off device

6.Press Vol down + Bixby + Power to reboot to download mode, press volume up when asked to continue to download mode

7Download Odin and open it, Disable 'Auto reboot' from option menu of Odin

8.Select TWRP (tar image) with AP tab of Odin and Start

9.Once Successfully flashed, you will see 'Passed' in Odin tab

10.Disconnect device and hold Vol down + power till screen goes off, Now immediately press Vol Up + Bixby + Power to reboot to TWRP

11.Select to allow modification

12.From TWRP, Select WIPE menu - Then FORMAT DATA - You need to type 'yes' to perform wipe. WARNING : This will erase all data including Int SD storage from device

13.Once format device completes, go back and select REBOOT' Menu and then - 'RECOVERY', This will reboot to TWRP again

14.Now select Install and navigate path to Ext SD card - Pie_G955F_Root_for_OEM_issue_devices_V*.zip, you have copied earlier

15.Once Magisk flash successfully, Reboot to System

Important Note for Pie - There will be OEM unlock option there in developer setting but it will be disabled and can not enabled, this is because of it is hacked. Just ignore it. You can not boot device with TWRP if it is really disabled. Also If magisk app may not appear then simply download Magisk_for_Pie.apk from below attachement and install as regular app.

Oreo

PS : This guide is for Oreo and will be updated for Pie, when Pie will be out officially.

This is for Stock ROM/Kernel only

If you have custom kernel, read below.

Here is guide and tool to Root S8/S8+ + Busybox + OEM Fix + Data mount fix

1.Enable Developer Option (settings - about phone - Software information - Tap 7 times on build number to activate developer option in settings menu)

2.Enable OEM Unlock from developer option (Currently no workaround for those who doesn't have this option)

3.Download and copy G955FD_Root_for_OEM_issue_devices_V*.zip to Ext SD card

4.Download TWRP latest TWRP (Edit : Latest TWRP is already fixed for data mount error, so you won't require to select data mount fix in aroma)

5.Switch Off device

6.Press Vol down + Bixby + Power to reboot to download mode, press volume up when asked to continue to download mode

7.Download Odin and open it, Disable 'Auto reboot' from option menu of Odin

8.Select TWRP (tar image) with AP tab of Odin and Start

9.Once Successfully flashed, you will see 'Passed' in Odin tab

10.Disconnect device and hold Vol down + power till screen goes off, Now immediately press Vol Up + Bixby + Power to reboot to TWRP

11.Select to allow modification

12.From TWRP, Select WIPE menu - Then FORMAT DATA - You need to type 'yes' to perform wipe. WARNING : This will erase all data including Int SD storage from device

13.Once format device completes, go back and select REBOOT' Menu and then - 'RECOVERY', This will reboot to TWRP again

14.Now select Install and navigate path to Ext SD card - G955FD_Root_for_OEM_issue_devices_V*.zip, you have copied earlier, select desired option (You must select Root option if you are on stock kernel/ROM else device won't boot) and select 'OEM Patch' option if your device have OEM issue. If you are not sure about this then better select 'OEM Patch', this will prevent losing OEM unlock option and so prevent 'custom binary error'

15.Once flash successfully finish, Reboot to System

Magisk app may appear in drawer after one reboot.

Open settings - Developer option - Look for OEM Unlock option. If it is there, it is safe to reboot device.

For custom Kernel, you need to flash modified recovery

that doesn't require data mount fix

YOU MUST BACKUP EFS AS SOON AS ROOT DEVICE, and copy it to safer place,

EFS Backup Tool

As soon as you root device, you must make backup of EFS and must store a copy of backup to safer place like on cloud and on a PC

XDA version - Free version, complimentary tools for XDA users.

Play Store version - You can buy from Play store to support us.

Both version make same form of backup and have no difference, Paid version have additional function to make Auto Backup when you change the ROM

Credits : [MENTION=631273]Chainfire[/MENTION] [MENTION=4470081]topjohnwu[/MENTION] [MENTION=6371894]jesec[/MENTION] [MENTION=6911575]BlackMesa123[/MENTION] for OEM fix[MENTION=4544860]osm0sis[/MENTION] and some International forum discussion for original idea