Reprogram TEE on Davinci

Guide to reprogram the TEE on Xiaomi Mi 9T / Redmi K20 devices to fix lost attestation keys.

Why?

If you are here it is because your phone has lost the TEE attestation keys, possibly due to flashing the persist partition of your phone.

If opening Key Attestation Demo does not give you any error, do NOT follow this guide.

This guide will NOT provide instructions for passing Strong verdict.

WARNINGS:

• Your data will be lost, so backup your phone data first.
• The original keys that your phone may include in the TEE will be lost.
• I am not responsible for any other problems that may arise, these instructions are made on a POCO X3 Pro (vayu) and work perfectly, they may not work as they should on other phones.

You will need:

• A working brain.
• A working computer.
• An unlocked bootloader.
• BASIC KNOWLEDGE OF LINUX.
• A valid keybox.xml file, you can use this one in the repo.
• The engineering ROM for your device.

Instructions:

1. Flash engineering ROM.
2. Phone must be connected to PC, then execute this commands IN ORDER:

adb root

adb disable-verity

adb reboot

adb root

adb remount

adb reboot

adb shell mkdir -p /data/nativetest64/qti_keymaster_tests/

adb push keybox.xml /data/nativetest64/qti_keymaster_tests/

adb shell LD_LIBRARY_PATH=/vendor/lib64/hw KmInstallKeybox /data/nativetest64/qti_keymaster_tests/keybox.xml 0 true

If you are using different keybox, you must change few arguments:

adb shell LD_LIBRARY_PATH=/vendor/lib64/hw KmInstallKeybox /data/nativetest64/qti_keymaster_tests/{KEYBOX FILE} {DEVICE ID} {ATTEST PROPS?}

Attest props must be true unless it gives some error.