blob: a072119574feb19c0608d16a9dfa417859a1ec1b [file] [log] [blame]
Sam Protsenkocd43fa12020-01-24 17:53:44 +02001.. SPDX-License-Identifier: GPL-2.0+
2
3Android Verified Boot 2.0
4=========================
5
6This file contains information about the current support of Android Verified
7Boot 2.0 in U-Boot.
8
9Overview
10--------
11
12Verified Boot establishes a chain of trust from the bootloader to system images:
13
14* Provides integrity checking for:
15
16 * Android Boot image: Linux kernel + ramdisk. RAW hashing of the whole
17 partition is done and the hash is compared with the one stored in
18 the VBMeta image
19 * ``system``/``vendor`` partitions: verifying root hash of dm-verity hashtrees
20
21* Provides capabilities for rollback protection
22
23Integrity of the bootloader (U-Boot BLOB and environment) is out of scope.
24
25For additional details check [1]_.
26
27AVB using OP-TEE (optional)
28^^^^^^^^^^^^^^^^^^^^^^^^^^^
29
30If AVB is configured to use OP-TEE (see `Enable on your board`_) rollback
31indexes and device lock state are stored in RPMB. The RPMB partition is managed
32by OP-TEE (see [2]_ for details) which is a secure OS leveraging ARM
33TrustZone.
34
35AVB 2.0 U-Boot shell commands
36-----------------------------
37
38Provides CLI interface to invoke AVB 2.0 verification + misc. commands for
39different testing purposes::
40
41 avb init <dev> - initialize avb 2.0 for <dev>
42 avb verify - run verification process using hash data from vbmeta structure
43 avb read_rb <num> - read rollback index at location <num>
44 avb write_rb <num> <rb> - write rollback index <rb> to <num>
45 avb is_unlocked - returns unlock status of the device
46 avb get_uuid <partname> - read and print uuid of partition <partname>
47 avb read_part <partname> <offset> <num> <addr> - read <num> bytes from
48 partition <partname> to buffer <addr>
49 avb write_part <partname> <offset> <num> <addr> - write <num> bytes to
50 <partname> by <offset> using data from <addr>
51
52Partitions tampering (example)
53------------------------------
54
55Boot or system/vendor (dm-verity metadata section) is tampered::
56
57 => avb init 1
58 => avb verify
59 avb_slot_verify.c:175: ERROR: boot: Hash of data does not match digest in
60 descriptor.
61 Slot verification result: ERROR_IO
62
63Vbmeta partition is tampered::
64
65 => avb init 1
66 => avb verify
67 avb_vbmeta_image.c:206: ERROR: Hash does not match!
68 avb_slot_verify.c:388: ERROR: vbmeta: Error verifying vbmeta image:
69 HASH_MISMATCH
70 Slot verification result: ERROR_IO
71
72Enable on your board
73--------------------
74
75The following options must be enabled::
76
77 CONFIG_LIBAVB=y
78 CONFIG_AVB_VERIFY=y
79 CONFIG_CMD_AVB=y
80
81In addtion optionally if storing rollback indexes in RPMB with help of
82OP-TEE::
83
84 CONFIG_TEE=y
85 CONFIG_OPTEE=y
86 CONFIG_OPTEE_TA_AVB=y
87 CONFIG_SUPPORT_EMMC_RPMB=y
88
89Then add ``avb verify`` invocation to your android boot sequence of commands,
90e.g.::
91
92 => avb_verify=avb init $mmcdev; avb verify;
93 => if run avb_verify; then \
94 echo AVB verification OK. Continue boot; \
95 set bootargs $bootargs $avb_bootargs; \
96 else \
97 echo AVB verification failed; \
98 exit; \
99 fi; \
100
101 => emmc_android_boot= \
102 echo Trying to boot Android from eMMC ...; \
103 ... \
104 run avb_verify; \
105 mmc read ${fdtaddr} ${fdt_start} ${fdt_size}; \
106 mmc read ${loadaddr} ${boot_start} ${boot_size}; \
107 bootm $loadaddr $loadaddr $fdtaddr; \
108
109If partitions you want to verify are slotted (have A/B suffixes), then current
110slot suffix should be passed to ``avb verify`` sub-command, e.g.::
111
112 => avb verify _a
113
114To switch on automatic generation of vbmeta partition in AOSP build, add these
115lines to device configuration mk file::
116
117 BOARD_AVB_ENABLE := true
118 BOARD_AVB_ALGORITHM := SHA512_RSA4096
119 BOARD_BOOTIMAGE_PARTITION_SIZE := <boot partition size>
120
121After flashing U-Boot don't forget to update environment and write new
122partition table::
123
124 => env default -f -a
125 => setenv partitions $partitions_android
126 => env save
127 => gpt write mmc 1 $partitions_android
128
129References
130----------
131
132.. [1] https://android.googlesource.com/platform/external/avb/+/master/README.md
133.. [2] https://www.op-tee.org/