tree b389467c4f5230592fda4016cdd0ee49ef19058b
parent 09543592072e9705ea7019c4633f3bcbc8621409
author Darren Krahn <dkrahn@google.com> 1517537194 -0800
committer Darren Krahn <dkrahn@google.com> 1519433820 -0800

Implement support for on-device persistent digests.

This feature allows digests from on-device persistent storage to be used
in place of digests embedded in descriptors. This allows verification of
partitions which hold per-device configuration data set during a factory
or provisioning stage and expected to remain unchanged from that point
forward.

Support is added for both 'hash' and 'hashtree' descriptors. In the case
of hashtree descriptors, the verity root digest needs to be added to the
kernel command line so this can be configured later without access to
AVB persistent storage. This is accomplished by supporting substitutions
of the form $(AVB_<part_name>_ROOT_DIGEST) where <part_name> is the
uppercase partition name. For example, if the partition name was
'factory' the kernel command line descriptor would hold:

 "androidboot.vbmeta.root_digest.factory=$(AVB_FACTORY_ROOT_DIGEST)"

The persistent value ops are designed to be reusable. Persistent values
are expected to be tamper-proof, similar to rollback indexes, and are
not expected to be available outside of the boot code running AVB.

Using persistent digests also requires that the partition not use A/B.
A new flag has been added to avbtool to support this as well as a
'flags' field in hash and hashtree descriptors.

This CL bumps the AVB version to 1.1 and any use of persistent digests
(or the --do_not_use_ab flag) will set the minimum libavb version in
vbmeta to 1.1. If these features are not used, the minimum remains 1.0.

Bug: 73020477
Test: Unit

Change-Id: Iffef31b232492bc8700ab8496c5da2ccfb49be44