Android 13’s new bootloader and anti-rollback on the Pixel 6

The latest iteration of Android comes with new UI improvements and functional features. The stable Android 13 update incremented the anti-rollback version in the bootloader of Pixel 6 devices. It means that once you upgrade your device to Android 13 then you can’t go back to an older version.

Do these devices Google Pixel 6/6 Pro/6a need an upgraded bootloader?

The rollback protection is materialized through electronic fuses on the Google Pixel 6, Pixel 6 Pro, and Pixel 6a devices. About an efuse, it’s a one-time flash. If you write something on the efuse then you can change that and the value written value on these stays forever. This new bootloader for the sixth generation stops installing an older version of Android on your device. The OTA of Android 13 is also responsible for that. The efuse increments its index only when successfully Android 13 is loaded on your device.

To know which bootloader is updated or older, exist in your Google Pixel 6, 6 Pro, 6a.

The job of the bootloader is to load the Operating System and chain-load another bootloader when the device starts. Google’s Fastboote utility will query the variables of an Android device from a computer. Here are steps on how to do Pixel device to its bootloader interface:

1. Make sure that you have the latest version of ADB and Fastboot utilities installed on your PC/Mac/Chromebook.
2. On your phone, go to Settings > About phone > Build number and tap on this entry 7 times to enable Developer options.
3. After enabling it, go back to the main settings page and tap on System, then go to Developer options.
4. Turn on USB debugging.
5. Connect your Pixel 6, Pixel 6 Pro, or Pixel 6a to your computer using a USB cable.
6. Open a terminal window and type the following command to check if your device is detected or not: ADB devices
7. Your phone should reboot to bootloader mode (also known as “Fastboot mode”).
8. Now, type the following command to check if the target device is detected by your PC in the bootloader mode: ADB reboot bootloader
9. Your phone should reboot to bootloader mode (also known as “Fastboot mode”).
10. Now, type the following command to check if the target device is detected by your PC in the bootloader mode: fastboot devices
11. To know the bootloader version, execute the command mentioned below: It is also possible to query the bootloader version from the user space Fastboot interface (aka fast boot). To do so, reboot the device using ADB reboot fast boot, then execute the same fast boot getvar version-bootloader command.

Those who don’t have a PC at the moment they can obtain a bootloader version from their smartphone. for this, you need to hold the Volume Down and Power buttons for some seconds and then release them when Fastboot mode appears on the screen. After that, you can locate the bootloader version on the screen.

Steps to safely upgrade the bootloader on Google Pixel 6/6 Pro/6a?

To not get into any issues you should install the bootloader partition to the inactive slot after successfully updating and booting into Android 13 at least once. This solves the problem of mismatch of version when you flash the Android 13 stable first time on these devices Pixel 6, Pixel 6 Pro, or Pixel 6a.

Option 1 (using recovery/OTA images):

After a successful boot into Android 13, download the full OTA image corresponding to that build. Next, sideload it from stock recovery and reboot the device to ensure that both slots have the same bootloader version.

Option 2 (using factory images):

People who upgraded to Android 13 by flashing the factory image after unlocking the bootloader should opt for this option. After a successful boot into Android 13 for the first time,

1. Check the currently active slot:
   ADB reboot bootloader
fastboot getvar current-slot
2. If the output returns the current slot as “a,” your active slot should be “a” and the other slot is “b.” If not, then your active slot is “b” and the other slot is “a.”
3. Extract the contents of the factory image ZIP file and locate the bootloader image in the extracted files. It should be named as “bootloader-[device codename]-[platform codename]-[major version]-[minor version].img.”
   • For the Pixel 6 and 6 Pro, the platform codename is “slider,” whereas, for the Pixel 6a, it’s “bluejay.”
4. Now, we need to flash the bootloader to both slots.
   1. If your active slot is ‘a’
      fastboot --slot=other flash bootloader bootloader_filename.image
fastboot set_active b
fastboot reboot bootloader
fastboot set_active a
fastboot reboot bootloader
fastboot reboot
   2. If your active slot is ‘b’
      fastboot --slot=other flash bootloader bootloader_filename.img
fastboot set_active a
fastboot reboot bootloader
fastboot set_active b
fastboot reboot bootloader
fastboot reboot
5. That’s all.

In this, you see different ways to check the bootloader version on your Pixel devices. You can choose the method which is suitable for you the most.

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