[U-Boot] [PATCH 8/8] doc: avb2.0: add README about AVB2.0 integration

[Sam Protsenko <semen.protsenko@linaro.org>]

On 25 April 2018 at 16:18, Igor Opaniuk <igor.opaniuk@linaro.org> wrote:
> Contains:
> 1. Overview of Android Verified Boot 2.0
> 2. Description of avb subset of commands
> 3. Examples of errors when boot/vendor/system/vbmeta partitions
> are tampered
> 4. Examples of enabling AVB2.0 on your setup
>
> Signed-off-by: Igor Opaniuk <igor.opaniuk@linaro.org>
> ---
>  doc/README.avb2 | 100 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 100 insertions(+)
>  create mode 100644 doc/README.avb2
>
> diff --git a/doc/README.avb2 b/doc/README.avb2
> new file mode 100644
> index 0000000..40db7c5
> --- /dev/null
> +++ b/doc/README.avb2
> @@ -0,0 +1,100 @@
> +Android Verified Boot 2.0
> +
> +This file contains information about the current support of Android Verified
> +Boot 2.0 in U-boot
> +
> +1. OVERVIEW
> +---------------------------------
> +Verified Boot establishes a chain of trust from the bootloader to system images
> +* Provides integrity checking for:
> +  - Android Boot image: Linux kernel + ramdisk. RAW hashing of the whole
> +    partition is done and the hash is compared with the one stored in
> +    the VBMeta image
> +  - system/vendor partitions: verifying root hash of dm-verity hashtrees.
> +* Provides capabilities for rollback protection.
> +
> +Integrity of the bootloader (U-boot BLOB and environment) is out of scope.
> +
> +For additional details check:
> +https://android.googlesource.com/platform/external/avb/+/master/README.md
> +
> +
> +2. AVB 2.0 U-BOOT SHELL COMMANDS
> +-----------------------------------
> +Provides CLI interface to invoke AVB 2.0 verification + misc. commands for
> +different testing purposes:
> +
> +avb init <dev> - initialize avb 2.0 for <dev>
> +avb verify - run verification process using hash data from vbmeta structure
> +avb read_rb <num> - read rollback index at location <num>
> +avb write_rb <num> <rb> - write rollback index <rb> to <num>
> +avb is_unlocked - returns unlock status of the device
> +avb get_uuid <partname> - read and print uuid of partition <partname>
> +avb read_part <partname> <offset> <num> <addr> - read <num> bytes from
> +partition <partname> to buffer <addr>
> +avb write_part <partname> <offset> <num> <addr> - write <num> bytes to
> +<partname> by <offset> using data from <addr>
> +
> +
> +3. PARTITIONS TAMPERING (EXAMPLE)
> +-----------------------------------
> +Boot or system/vendor (dm-verity metadata section) is tampered:
> +=> avb init 1
> +=> avb verify
> +avb_slot_verify.c:175: ERROR: boot: Hash of data does not match digest in
> +descriptor.
> +Slot verification result: ERROR_IO
> +
> +Vbmeta partition is tampered:
> +=> avb init 1
> +=> avb verify
> +avb_vbmeta_image.c:206: ERROR: Hash does not match!
> +avb_slot_verify.c:388: ERROR: vbmeta: Error verifying vbmeta image:
> +HASH_MISMATCH
> +Slot verification result: ERROR_IO
> +
> +
> +4. ENABLE ON YOUR BOARD
> +-----------------------------------
> +The following options must be enabled:
> +CONFIG_LIBAVB=y
> +CONFIG_LIBAVB_AB=y
> +CONFIG_CMD_AVB=y
> +
> +
> +Then add `avb verify` invocation to your android boot sequence of commands,
> +e.g.:
> +
> +=> avb_verify=avb init $mmcdev; avb verify;
> +=> if run avb_verify; then                       \
> +        echo AVB verification OK. Continue boot; \
> +        set bootargs $bootargs $avb_bootargs;    \
> +   else                                          \
> +        echo AVB verification failed;            \
> +        exit;                                    \
> +   fi;                                           \
> +
> +=> emmc_android_boot=                                   \
> +       echo Trying to boot Android from eMMC ...;       \
> +       ...                                              \
> +       run avb_verify;                                  \
> +       mmc read ${fdtaddr} ${fdt_start} ${fdt_size};    \
> +       mmc read ${loadaddr} ${boot_start} ${boot_size}; \
> +       bootm $loadaddr $loadaddr $fdtaddr;              \
> +
> +
> +To switch on automatic generation of vbmeta partition in AOSP build, add these
> +lines to device configuration mk file:
> +
> +BOARD_AVB_ENABLE := true
> +BOARD_AVB_ALGORITHM := SHA512_RSA4096
> +BOARD_BOOTIMAGE_PARTITION_SIZE := <boot partition size>
> +
> +After flashing U-boot don't forget to update environment and write new
> +partition table:
> +=> env default -f -a
> +=> setenv partitions $partitions_android
> +=> env save
> +=> fas 1
> +
> +$ fastboot oem format

FYI, those commands can be shrank down to a single command:

    => gpt write mmc 1 $partitions_android

because that's exactly what "fastboot oem format" is doing. This way
you can avoid using fastboot, and thus having it as a dependency. But
your way is better w.r.t. user experience (i.e. if environment is
already set, user can just run host command, and avoid tinkering with
U-Boot shell at all). Please choose which one is better depending on
targeting use-case.

> --
> 2.7.4
>