1## 9.10\. Device Integrity
2
3The following requirements ensure there is transparency to the status of the
4device integrity. Device implementations:
5
6*    [C-0-1] MUST correctly report through the System API method
7`PersistentDataBlockManager.getFlashLockState()` whether their bootloader
8state permits flashing of the system image. The `FLASH_LOCK_UNKNOWN` state is
9reserved for device implementations upgrading from an earlier version of Android
10where this new system API method did not exist.
11
12*    [C-0-2] MUST support Verified Boot for device integrity.
13
14If device implementations are already launched without supporting Verified Boot
15on an earlier version of Android and can not add support for this
16feature with a system software update, they MAY be exempted from the
17requirement.
18
19Verified Boot is a feature that guarantees the integrity of the device
20software. If device implementations support the feature, they:
21
22*    [C-1-1] MUST declare the platform feature flag
23`android.software.verified_boot`.
24*    [C-1-2] MUST perform verification on every boot sequence.
25*    [C-1-3] MUST start verification from an immutable hardware key that is the
26root of trust and go all the way up to the system partition.
27*    [C-1-4] MUST implement each stage of verification to check the integrity
28and authenticity of all the bytes in the next stage before executing the code in
29the next stage.
30*    [C-1-5] MUST use verification algorithms as strong as current
31recommendations from NIST for hashing algorithms (SHA-256) and public key
32sizes (RSA-2048).
33*    [C-1-6] MUST NOT allow boot to complete when system verification fails,
34unless the user consents to attempt booting anyway, in which case the data from
35any non-verified storage blocks MUST not be used.
36*    [C-1-7] MUST NOT allow verified partitions on the device to be modified
37unless the user has explicitly unlocked the bootloader.
38*    [C-SR] If there are multiple discrete chips in the device (e.g. radio,
39specialized image processor), the boot process of each of those chips is
40STRONGLY RECOMMENDED to verify every stage upon booting.
41*    [C-1-8] MUST use tamper-evident storage: for storing whether the
42bootloader is unlocked. Tamper-evident storage means that the bootloader can
43detect if the storage has been tampered with from inside Android.
44*    [C-1-9] MUST prompt the user, while using the device, and
45require physical confirmation before allowing a transition from bootloader
46locked mode to bootloader unlocked mode.
47*    [C-1-10] MUST implement rollback protection for partitions used by Android
48(e.g. boot, system partitions) and use tamper-evident storage for storing the
49metadata used for determining the minimum allowable OS version.
50*    [C-SR] Are STRONGLY RECOMMENDED to verify all privileged app APK files with
51a chain of trust rooted in partitions protected by Verified Boot.
52*    [C-SR] Are STRONGLY RECOMMENDED to verify any executable artifacts loaded by
53a privileged app from outside its APK file (such as dynamically loaded code or
54compiled code) before executing them or STRONGLY RECOMMENDED not to execute them
55at all.
56*    SHOULD implement rollback protection for any component with persistent
57firmware (e.g. modem, camera) and SHOULD use tamper-evident storage for
58storing the metadata used for determining the minimum allowable version.
59
60If device implementations are already launched without supporting C-1-8 through
61C-1-10 on an earlier version of Android and can not add support for
62these requirements with a system software update, they MAY be exempted from the
63requirements.
64
65The upstream Android Open Source Project provides a preferred implementation of
66this feature in the [`external/avb/`](
67http://android.googlesource.com/platform/external/avb/)
68repository, which can be integrated into the bootloader used for loading
69Android.
70
71Device implementations:
72
73*    [C-R] Are RECOMMENDED to support the [Android Protected Confirmation API](
74https://developer.android.com/preview/features/security.html#user-confirmation).
75
76If device implementations support the Android Protected Confirmation
77API they:
78
79*    [C-3-1] MUST report `true` for the [`ConfirmationPrompt.isSupported()`](
80https://developer.android.com/reference/android/security/ConfirmationPrompt.html#isSupported%28android.content.Context%29)
81API.
82
83*    [C-3-2] MUST ensure that code running in the Android OS including its
84     kernel, malicious or otherwise, cannot generate a positive response without
85     user interaction.
86
87*    [C-3-3] MUST ensure that the user has been able to review and approve the
88     prompted message even in the event that the Android OS, including its kernel,
89     is compromised.
90