Building GrapheneOS
Build targets
Smartphone targets:
- raven (Pixel 6 Pro) — not yet supported but ready to be worked on
- oriole (Pixel 6) — not yet supported but ready to be worked on
- barbet (Pixel 5a)
- redfin (Pixel 5)
- bramble (Pixel 4a (5G))
- sunfish (Pixel 4a)
- coral (Pixel 4 XL)
- flame (Pixel 4)
- bonito (Pixel 3a XL)
- sargo (Pixel 3a)
- crosshatch (Pixel 3 XL)
- blueline (Pixel 3)
These are all fully supported production-ready targets supporting all the baseline security features and receiving full monthly security updates covering all firmware, kernel drivers, driver libraries / services and other device-specific code. A fully signed user build for these devices is a proper GrapheneOS release. Newer generation devices have stronger hardware / firmware security and hardware-based OS security features and are better development devices for that reason. It's not possible to work on everything via past generation devices. The best development devices are the Pixel 5 and Pixel 4a (5G).
Generic targets:
- aosp_arm
- aosp_arm64
- aosp_mips
- aosp_mips64
- aosp_x86
- aosp_x86_64
These generic targets can be used with the emulator along with many smartphones, tablets and other devices. These targets don't receive full monthly security updates, don't offer all of the baseline security features and are intended for development usage.
Providing proper support for a device or generic device family requires providing an up-to-date kernel and device support code including driver libraries, firmware and device SELinux policy extensions. Other than some special cases like the emulator, the generic targets rely on the device support code present on the device. Shipping all of this is necessary for full security updates and is tied to enabling verified boot / attestation. Pixel targets have a lot of device-specific hardening in the AOSP base along with some in GrapheneOS which needs to be ported over too. For example, various security features in the kernel including type-based Control Flow Integrity (CFI) and the shadow call stack are currently specific to the kernels for these devices.
SDK emulator targets:
- sdk_phone_armv7
- sdk_phone_arm64
- sdk_phone_mips
- sdk_phone_mips64
- sdk_phone_x86
- sdk_phone_x86_64
These are extended versions of the generic targets with extra components for the SDK. These targets don't receive full monthly security updates, don't provide all of the baseline security features and are intended for development usage.
Build dependencies
Arch Linux, Debian buster and Ubuntu 20.04 LTS are the officially supported operating systems for building GrapheneOS.
Dependencies for fetching and verifying the sources:
- repo
- python3 (for repo)
- git (both for repo and manual usage)
- gpg (both for repo and manual usage)
- 131GiB+ storage for a standard sync with history, 61GiB+ storage for a lightweight sync
Baseline build dependencies:
- x86_64 Linux build environment (macOS is not supported, unlike AOSP which partially supports it)
- Android Open Source Project build dependencies
- 16GiB of memory or more. Link-Time Optimization (LTO) creates huge peaks during linking and is mandatory for Control Flow Integrity (CFI). Linking Vanadium (Chromium) and the Linux kernel with LTO + CFI are the most memory demanding tasks.
- 100GiB+ of additional free storage space for a typical build of the entire OS for a multiarch device
- en_US.UTF-8 locale supported
You can either obtain repo as a distribution package or the
self-updating standalone version from the Android Open Source Project. The
self-updating variant avoids dealing with out-of-date distribution packages and
depends on GPG to verify updates.
The Android Open Source Project build system is designed to provide reliable and reproducible builds. To accomplish this, it provides a prebuilt toolchain and other utilities fulfilling most of the build dependency requirements itself. These prebuilt tools have reproducible builds themselves. It runs the build process within a loose sandbox to avoid accidental dependencies on the host system. The process of moving to a fully self-contained build process with minimal external dependencies is gradual and there are still dependencies that need to be installed on the host system.
The Linux kernel build process is not integrated into the rest of the AOSP build process, but does reuse the same prebuilts to make the build reproducible.
Additional Linux kernel build dependencies not provided by the source tree:
- libgcc (for the host, not the target)
- binutils (for the host, not the target)
The dependency on the host libgcc and binutils for building utilities during the build process will be phased out by moving to a pure LLVM-based toolchain alongside doing it for the target. This is lagging a bit behind for the kernel, particularly code built for the host.
Additional Android Open Source Project build dependencies not provided by the source tree:
- diff (diffutils)
- freetype2 and any OpenType/TrueType font (such as DejaVu but anything works) for OpenJDK despite it being a headless variant without GUI support
- ncurses5 (provided by the source tree for some tools but not others)
- openssl
- rsync
- unzip
- zip
Additional android-prepare-vendor (for Pixel phones) dependencies:
- e2fsprogs (for debugfs)
- OpenJDK (for the jar command)
- protobuf library for Python 3
- jq
Additional Vanadium (Chromium) build dependencies not provided by the source tree:
- 32-bit glibc
- 32-bit gcc runtime library
The signify tool (with the proper naming) is also required for signing
factory images zips.
Downloading source code
Since this is syncing the sources for the entire operating system and application layer, it will use a lot of bandwidth and storage space.
You likely want to use the most recent stable tag, not the development branch, even for developing a feature. It's easier to port between stable tags that are known to work properly than dealing with a moving target.
Development branch
The 12 branch is the active developed branch of
GrapheneOS. It follows along with the latest stable releases of the
Android Open Source Project which currently means the latest monthly
release of the android12-release (Android 12) branch. The
12 branch of GrapheneOS should be used for all officially
supported devices and porting to other devices.
mkdir grapheneos-12 cd grapheneos-12 repo init -u https://github.com/GrapheneOS/platform_manifest.git -b 12 repo sync -j32
If your network is unreliable and repo sync fails, you can run the
repo sync command again to continue from where it was interrupted. It
handles connection failures robustly and you shouldn't start over from scratch.
Stable release
Pick a specific release for a device from the releases page and download the source tree. Note that some devices use different Android Open Source Project branches so they can end up with different tags. Make sure to use the correct tag for a device. For devices without official support, use the latest tag marked as being appropriate for generic / other devices in the release notes.
mkdir grapheneos-TAG_NAME cd grapheneos-TAG_NAME repo init -u https://github.com/GrapheneOS/platform_manifest.git -b refs/tags/TAG_NAME
Verify the manifest:
gpg --recv-keys 65EEFE022108E2B708CBFCF7F9E712E59AF5F22A cd .repo/manifests git verify-tag $(git describe) cd ../..
Complete the source tree download:
repo sync -j32
The manifest for the latest stable release refers to the revisions in other repositories via commit hashes rather than tag names. This avoids the need to use a script to verify tag signatures across all the repositories, since they simply point to the same commits with the same hashes.
Note that the repo command itself takes care of updating itself and uses GPG to verify by default.
Kernel
The kernel needs to be built in advance, since it uses a separate build system.
Prebuilts are provided for all the officially supported devices, so this step is optional.
List of kernels corresponding to officially supported devices:
-
Pixel 3, Pixel 3 XL, Pixel 3a, Pixel 3a XL: crosshatch
- Pixel 3: blueline
- Pixel 3 XL: crosshatch
- Pixel 3a, Pixel 3a XL: bonito
-
Pixel 4, Pixel 4 XL, Pixel 4a: coral
- Pixel 4, Pixel 4 XL: coral
- Pixel 4a: sunfish
-
Pixel 4a (5G), Pixel 5: redbull
- Pixel 4a (5G): bramble
- Pixel 5: redfin
- Pixel 5a: barbet
- Pixel 6: raviole
As part of the hardening in GrapheneOS, it uses fully monolithic kernel builds with dynamic kernel modules disabled. This improves the effectiveness of mitigations like Control Flow Integrity benefiting from whole program analysis. It also reduces attack surface and complexity including making the build system simpler. The kernel trees marked as using a separate build above need to have the device variant passed to the GrapheneOS kernel build script to select the device.
The kernel repositories use submodules for building in out-of-tree modules.
You need to make sure the submodule sources are updated before building. In
the future, this should end up being handled automatically by
repo. There's no harm in running the submodule commands for other
devices as they will simply not do anything.
For example, to build the kernel for redfin:
cd kernel/google/redbull git submodule sync git submodule update --init --recursive ./build.sh redfin
Setting up the OS build environment
The build has to be done from bash as envsetup.sh is not compatible with other shells like zsh.
Set up the build environment:
source script/envsetup.sh
Select the desired build target (redfin is the Pixel 5):
choosecombo release redfin user
For a development build, you may want to replace user with
userdebug in order to have better debugging support. Production builds
should be user builds as they are significantly more secure and don't
make additional performance sacrifices to improve debugging.
Set OFFICIAL_BUILD=true to include the Updater app. You
must change the URL in
packages/apps/Updater/res/values/config.xml to your own update server
URL. Using the official update server with a build signed with different keys will not
work and will essentially perform a denial of service attack on our update service. If
you try to use the official URL, the app will download an official update and will
detect it as corrupted or tampered. It will delete the update and try to download it
over and over again since it will never be signed with your key.
export OFFICIAL_BUILD=true
Reproducible builds
To reproduce a past build, you need to export BUILD_DATETIME and
BUILD_NUMBER to the values set for the past build. These can be obtained
from out/build_date.txt and out/build_number.txt in a build
output directory and the ro.build.date.utc and
ro.build.version.incremental properties which are also included in the
over-the-air zip metadata rather than just the OS itself.
The signing process for release builds is done after completing builds and replaces the dm-verity trees, apk signatures, etc. and can only be reproduced with access to the same private keys. If you want to compare to production builds signed with different keys you need to stick to comparing everything other than the signatures.
Additionally, set OFFICIAL_BUILD=true per the instructions above to
reproduce the official builds. Note that if you do not change the URL to your own
domain, you must disable the Updater app before connecting the device
to the internet, or you will be performing a denial of service attack on our official
update server.
Extracting vendor files for Pixel devices
This section is specific to Pixel devices. The emulator and generic targets don't require extra vendor files.
Many of these components are already open source, but not everything is set up to be built by the Android Open Source Project build system. Switching to building these components from source will be an incremental effort. In many cases, the vendor files simply need to be ignored and AOSP will already provide them instead. Firmware cannot generally be built from source even when sources are available, other than to verify that the official builds match the sources, since it has signature verification (which is an important part of the verified boot and attestation security model).
Extract the vendor files corresponding to the matching release with
DEVICE and BUILD_ID replaced with the appropriate
values:
vendor/android-prepare-vendor/execute-all.sh -d DEVICE -b BUILD_ID -o vendor/android-prepare-vendor mkdir -p vendor/google_devices rm -rf vendor/google_devices/DEVICE mv vendor/android-prepare-vendor/DEVICE/BUILD_ID/vendor/google_devices/* vendor/google_devices/
Note that android-prepare-vendor is non-deterministic unless a timestamp parameter is
passed with --timestamp (seconds since Epoch).
Building
Incremental builds (i.e. starting from the old build) usually work for development and are the normal way to develop changes. However, there are cases where changes are not properly picked up by the build system. For production builds, you should remove the remnants of any past builds before starting, particularly if there were non-trivial changes:
rm -r out
Next, start the build process with the m command:
m target-files-package
The -j parameter can be passed to m to set a specific
number of jobs such as -j4 to use 4 jobs. By default, the build system
sets the number of jobs to NumCPU() + 2 where NumCPU() is the
number of available logical CPUs.
For an emulator build, always use the development build approach below.
Faster builds for development use only
The normal production build process involves building a target files package to be resigned with secure release keys and then converted into factory images and/or an update zip via the sections below. If you have a dedicated development device with no security requirements, you can save time by using the default build target rather than target-files-package. Leave the bootloader unlocked and flashing the raw images that are signed with the default public test keys.
To build the default build target:
m
Technically, you could generate test key signed update packages. However, there's no point of sideloading update packages when the bootloader is unlocked and there's no value in a locked bootloader without signing the build using release keys, since verified boot will be meaningless and the keys used to verify sideloaded updates are also public. The only reason to use update packages or a locked bootloader without signing the build with release keys would be testing that functionality and it makes a lot more sense to test it with proper signing keys rather than the default public test keys.
Generating release signing keys
Keys need to be generated for resigning completed builds from the publicly available test keys. The keys must then be reused for subsequent builds and cannot be changed without flashing the generated factory images again which will perform a factory reset. Note that the keys are used for a lot more than simply verifying updates and verified boot.
The sample certificate subject (CN=GrapheneOS) should be replaced with
your own information.
You should set a passphrase for the signing keys to keep them at rest until you
need to sign a release with them. The GrapheneOS scripts (make_key and
encrypt_keys.sh) encrypt the signing keys using scrypt for key derivation
and AES256 as the cipher. If you use swap, make sure it's encrypted, ideally with an
ephemeral key rather a persistent key to support hibernation. Even with an ephemeral
key, swap will reduce the security gained from encrypting the keys since it breaks the
guarantee that they become at rest as soon as the signing process is finished.
Consider disabling swap, at least during the signing process.
The encryption passphrase for all the keys generated for a device needs to match for compatibility with the GrapheneOS scripts.
To generate keys for redfin (you should use unique keys per device variant):
mkdir -p keys/redfin cd keys/redfin ../../development/tools/make_key releasekey '/CN=GrapheneOS/' ../../development/tools/make_key platform '/CN=GrapheneOS/' ../../development/tools/make_key shared '/CN=GrapheneOS/' ../../development/tools/make_key media '/CN=GrapheneOS/' ../../development/tools/make_key networkstack '/CN=GrapheneOS/' openssl genrsa 4096 | openssl pkcs8 -topk8 -scrypt -out avb.pem ../../external/avb/avbtool extract_public_key --key avb.pem --output avb_pkmd.bin cd ../..
The avb_pkmd.bin file isn't needed for generating a signed release but
rather to set the public key used by the device to enforce verified boot.
Generate a signify key for signing factory images:
signify -G -n -p keys/redfin/factory.pub -s keys/redfin/factory.sec
Remove the -n switch to set a passphrase. The signify
tool doesn't provide a way to change the passphrase without generating a new key, so
this is currently handled separately from encrypting the other keys and there will be
a separate prompt for the passphrase. In the future, expect this to be handled by the
same scripts along with the expectation of it using the same passphrase as the other
keys.
Encrypting keys
You can (re-)encrypt your signing keys using the encrypt_keys script,
which will prompt for the old passphrase (if any) and new passphrase:
script/encrypt_keys.sh keys/redfin
The script/decrypt_keys.sh script can be used to remove encryption,
which is not recommended. The script exists primarily for internal usage to decrypt
the keys in tmpfs to perform signing.
Enabling updatable APEX components
GrapheneOS disables updatable APEX components for the officially supported devices and targets inheriting from the mainline target, so APEX signing keys are not needed and this section can be ignored for unmodified builds.
GrapheneOS uses the TARGET_FLATTEN_APEX := true format to include APEX
components as part of the base OS without supporting out-of-band updates.
If you don't disable updatable APEX packages, you need to generate an APK and AVB key for each APEX component and extend the GrapheneOS release.sh script to pass the appropriate parameters to replace the APK and AVB keys for each APEX component.
APEX components that are not flattened are a signed APK (used to verify updates) with an embedded filesystem image signed with an AVB key (for verified boot). Each APEX package must have a unique set of keys. GrapheneOS has no use for these out-of-band updates at this time and flattening APEX components avoids needing a bunch of extra keys and complexity.
For now, consult the upstream documentation on generating these keys. It will be covered here in the future.
Generating signed factory images and full update packages
Build and package up the tools needed to generate over-the-air update packages:
m otatools-package
Generate a signed release build with the release.sh script:
script/release.sh redfin
The factory images and update package will be in
out/release-redfin-$BUILD_NUMBER. The update zip performs a full OS
installation so it can be used to update from any previous version. More efficient
incremental updates are used for official over-the-air GrapheneOS updates and can be
generated by keeping around past signed target_files zips and generating
incremental updates from those to the most recent signed target_files
zip.
See the install page for information on how to use the factory images. See the usage guide section on sideloading updates for information on how to use the update packages.
Running script/release.sh also generates channel metadata for the
update server. If you configured the Updater client URL and set the build to include
it (see the information on OFFICIAL_BUILD above), you can push signed
over-the-air updates via the update system. Simply upload the update package to the
update server along with the channel metadata for the release channel, and it will be
pushed out to the update client. The $DEVICE-beta and
$DEVICE-stable metadata provide the Beta and Stable release channels used
by the update client. The $DEVICE-testing metadata provides
an internal testing channel for the OS developers, which can be temporarily
enabled using adb shell setprop sys.update.channel testing. The name is
arbitrary and you can also use any other name for internal testing channels.
For GrapheneOS itself, the testing channel is used to push out updates to developer devices, followed by a sample future release to test that the release which is about to be pushed out to the Beta channel is able to update to a future release. Once it's tested internally, the release is pushed out to the Beta channel, and finally to the Stable channel after public testing. A similar approach is recommended for derivatives of GrapheneOS.
Generating delta updates
Incremental updates shipping only the changes between two versions can be generated
as a much more efficient way of shipping updates than a full update package containing
the entire operating system. The GrapheneOS Updater app will automatically use a delta
update if one exists for going directly from the currently installed version to the
latest release. In order to generate a delta update, the original signed target files
package for both the source version and target version are needed. The
script/generate_delta.sh script provides a wrapper script for generating
delta updates by passing the device, source version build number and target version
build number. For example:
script/generate_delta.sh redfin 2021102503 2021102613
The script assumes that the releases are organized in the following directory structure:
releases
├── 2021102503
│ └── release-redfin-2021102503
│ ├── otatools
│ ├── redfin-beta
│ ├── redfin-factory-2021102503.zip
│ ├── redfin-factory-2021102503.zip.sig
│ ├── redfin-img-2021102503.zip
│ ├── redfin-ota_update-2021102503.zip
│ ├── redfin-stable
│ ├── redfin-target_files-2021102503.zip
│ └── redfin-testing
└── 2021102613
└── release-redfin-2021102613
├── otatools
├── redfin-beta
├── redfin-factory-2021102613.zip
├── redfin-factory-2021102613.zip.sig
├── redfin-img-2021102613.zip
├── redfin-ota_update-2021102613.zip
├── redfin-stable
├── redfin-target_files-2021102613.zip
└── redfin-testing
Incremental updates are uploaded alongside the update packages and update metadata on the static web server used as an update server. The update client will automatically check for an incremental update and use it if available. No additional metadata is needed to make incremental updates work.