1Android Verified Boot 2.0 2 3This file contains information about the current support of Android Verified 4Boot 2.0 in U-boot 5 61. OVERVIEW 7--------------------------------- 8Verified Boot establishes a chain of trust from the bootloader to system images 9* Provides integrity checking for: 10 - Android Boot image: Linux kernel + ramdisk. RAW hashing of the whole 11 partition is done and the hash is compared with the one stored in 12 the VBMeta image 13 - system/vendor partitions: verifying root hash of dm-verity hashtrees. 14* Provides capabilities for rollback protection. 15 16Integrity of the bootloader (U-boot BLOB and environment) is out of scope. 17 18For additional details check: 19https://android.googlesource.com/platform/external/avb/+/master/README.md 20 21 222. AVB 2.0 U-BOOT SHELL COMMANDS 23----------------------------------- 24Provides CLI interface to invoke AVB 2.0 verification + misc. commands for 25different testing purposes: 26 27avb init <dev> - initialize avb 2.0 for <dev> 28avb verify - run verification process using hash data from vbmeta structure 29avb read_rb <num> - read rollback index at location <num> 30avb write_rb <num> <rb> - write rollback index <rb> to <num> 31avb is_unlocked - returns unlock status of the device 32avb get_uuid <partname> - read and print uuid of partition <partname> 33avb read_part <partname> <offset> <num> <addr> - read <num> bytes from 34partition <partname> to buffer <addr> 35avb write_part <partname> <offset> <num> <addr> - write <num> bytes to 36<partname> by <offset> using data from <addr> 37 38 393. PARTITIONS TAMPERING (EXAMPLE) 40----------------------------------- 41Boot or system/vendor (dm-verity metadata section) is tampered: 42=> avb init 1 43=> avb verify 44avb_slot_verify.c:175: ERROR: boot: Hash of data does not match digest in 45descriptor. 46Slot verification result: ERROR_IO 47 48Vbmeta partition is tampered: 49=> avb init 1 50=> avb verify 51avb_vbmeta_image.c:206: ERROR: Hash does not match! 52avb_slot_verify.c:388: ERROR: vbmeta: Error verifying vbmeta image: 53HASH_MISMATCH 54Slot verification result: ERROR_IO 55 56 574. ENABLE ON YOUR BOARD 58----------------------------------- 59The following options must be enabled: 60CONFIG_LIBAVB=y 61CONFIG_AVB_VERIFY=y 62CONFIG_CMD_AVB=y 63 64 65Then add `avb verify` invocation to your android boot sequence of commands, 66e.g.: 67 68=> avb_verify=avb init $mmcdev; avb verify; 69=> if run avb_verify; then \ 70 echo AVB verification OK. Continue boot; \ 71 set bootargs $bootargs $avb_bootargs; \ 72 else \ 73 echo AVB verification failed; \ 74 exit; \ 75 fi; \ 76 77=> emmc_android_boot= \ 78 echo Trying to boot Android from eMMC ...; \ 79 ... \ 80 run avb_verify; \ 81 mmc read ${fdtaddr} ${fdt_start} ${fdt_size}; \ 82 mmc read ${loadaddr} ${boot_start} ${boot_size}; \ 83 bootm $loadaddr $loadaddr $fdtaddr; \ 84 85 86To switch on automatic generation of vbmeta partition in AOSP build, add these 87lines to device configuration mk file: 88 89BOARD_AVB_ENABLE := true 90BOARD_AVB_ALGORITHM := SHA512_RSA4096 91BOARD_BOOTIMAGE_PARTITION_SIZE := <boot partition size> 92 93After flashing U-boot don't forget to update environment and write new 94partition table: 95=> env default -f -a 96=> setenv partitions $partitions_android 97=> env save 98=> gpt write mmc 1 $partitions_android 99