Starting with Android 8.0 Oreo, Google introduced the 'rollback protection' mechanism to prevent the old version from being swiped back to the old version. The purpose of this is for higher security, and the second is to improve the fragmentation with Project Treble. Speed up the system iteration.
Today (August 7th), Google officially pushed the Android 9 Pie system, and the four Pixels and Essential PH-1 were first upgraded. At the same time, the source code of Android 9 Pie was also submitted to AOSP. According to XDA mining, Android 9 Pie , 'rollback protection' changed from recommended to mandatory, including OEMs.
The implementation of 'anti-rollback' relies on the new Android Verified Boot 2.0 (Verified Boot 2.0). Even if the user is successful, the startup mechanism will refuse to start after detecting that the current version is lower than the previous version. In the Android 8.0 device, Pixel 2, Razer mobile phone, one plus 6 are integrated with this feature.
In the compatibility guide of the Android 9 Pie system, the boot/system/vendor three partitions have added 'rollback protection', but the baseband and camera are not. It may be because most security deployments are for the first three partitions. For the sake of it.
