(Outdated) System Upgrades#

⚠️ FIXME. ⚠️

This page is just a stub that needs to be completed. You can open a PR on the repo to add more content to the page.

Removed in version 3.11.2.5: See System Upgrades for the latest documentation

Update Systemd Service#

update-engine.service

DBus Interface#

<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
  "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<busconfig>
  <policy user="root">
    <allow own="no.remarkable.update1" />
    <allow send_destination="no.remarkable.update1" />
  </policy>
  <policy user="core">
    <!-- introspection is denied -->
    <deny send_destination="no.remarkable.update1"
          send_interface="org.freedesktop.DBus.Introspectable" />
    <!-- properties denied -->
    <deny send_destination="no.remarkable.update1"
          send_interface="org.freedesktop.DBus.Properties" />
    <!-- allow explicit methods -->
    <allow send_destination="no.remarkable.update1"
           send_interface="no.remarkable.update1.Manager"
           send_member="AttemptUpdate"/>
    <allow send_destination="no.remarkable.update1"
           send_interface="no.remarkable.update1.Manager"
           send_member="ResetStatus"/>
    <allow send_destination="no.remarkable.update1"
           send_interface="no.remarkable.update1.Manager"
           send_member="GetStatus"/>
  </policy>
  <policy context="default">
    <deny send_destination="no.remarkable.update1" />
  </policy>
</busconfig>

Command Line Interface#

$ update_engine_client -status
$ update_engine_client -reset_status
$ update_engine_client -check_for_update
$ update_engine_client -update
$ update_engine_client -watch_for_updates

Update File Format#

The protobuf definition of the update file format can be found in update_metadata.proto.

struct delta_update_file {
    // Magic characters to identify an update file
    char magic[4] = "CrAU";
    uint64 file_format_version = 1;

    // Size of protobuf DeltaArchiveManifest
    uint64 manifest_size;
    // The Bzip2 compressed DeltaArchiveManifest
    char manifest[];

    // Data blobs for files, no specific format.
    // The specific offset and length of each
    // data blob is recorded in the
    // DeltaArchiveManifest.
    struct {
        char data[];
    } blobs[];

    // Size of protobuf Signatures
    uint64 signatures_message_size;
    // Signatures attached to the update file.
    char signatures_message[];
};

DeltaArchiveManifest#

message DeltaArchiveManifest {
  // Steps to replace a root partititon with the new
  // data. When finished, the replaced partititon
  // should match the hash provided in
  // new_partition_info
  repeated InstallOperation partition_operations = 1;

  // A dummy operation to ensure that the
  // signatures data is ignored while
  // running partition_operations
  repeated InstallOperation noop_operations = 2;

  optional uint32 block_size = 3 [default = 4096];
  optional uint64 signatures_offset = 4;
  optional uint64 signatures_size = 5;

  // Partition data that can be used to validate
  // the update. reMarkable doesn't appear to
  // use old_partition_info
  optional InstallInfo old_partition_info = 8;
  optional InstallInfo new_partition_info = 9;

  // This appears to be unused.
  repeated InstallProcedure procedures = 10;
}

InstallProcedure#

message Extent {
  optional uint64 start_block = 1;
  optional uint64 num_blocks = 2;
}

message InstallOperation {
  enum Type {
    // Replace destination with attached data
    REPLACE = 0;
    // Replace destination with attached
    // bzipped data
    REPLACE_BZ = 1;
    // Move data from source to destination
    // Appears to be unused
    MOVE = 2;
    // The data is a bsdiff binary diff
    // Appears to be unused
    BSDIFF = 3;
  }
  required Type type = 1;

  // Offset after the manifest in the update file
  // that contains data for this install operation
  optional uint32 data_offset = 2;
  // The length of the data for this install
  // operation
  optional uint32 data_length = 3;

  // Appears to be unused
  repeated Extent src_extents = 4;
  // Only used for Type == REPLACE_BZ
  optional uint64 src_length = 5;

  // Location to update on the root partition
  repeated Extent dst_extents = 6;
  // Only used for Type == REPLACE_BZ
  optional uint64 dst_length = 7;

  // SHA 256 hash of the blob if it has one
  optional bytes data_sha256_hash = 8;
}

The following example python code can be used to extract the ext4 image from an update file:

import bz2
import struct

from hashlib import sha256

# This file will need to be generated from
# update_metadata.proto
from .update_metadata_pb2 import DeltaArchiveManifest
from .update_metadata_pb2 import InstallOperation

with open("update.signed", 'rb') as f, open("update.ext4", 'wb') as o:
    if f.read(4) != b"CrAU":
        raise Exception("Wrong header")

    major = struct.unpack(">Q", f.read(8))[0]
    if major != 1:
        raise Exception("Unsupported version")

    size = struct.unpack(">Q", f.read(8))[0]
    data = f.read(size)
    manifest = DeltaArchiveManifest.FromString(data)
    offset = f.tell()
    block_size = manifest.block_size

    for blob in manifest.partition_operations:
        if blob.type not in (0, 1):
            raise Exception(f"Unsupported type {blob.type}")

        extent = blob.dst_extents[0]
        dst_offset = extent.start_block * block_size
        dst_length = extent.num_blocks * block_size

        f.seek(offset + blob.data_offset)
        data = f.read(blob.data_length)
        if sha256(data).digest() != blob.data_sha256_hash:
            raise Exception("Data has wrong sha256sum")

        if blob.type == InstallOperation.Type.REPLACE_BZ:
            data = bz2.decompress(data)

        if dst_length - len(data) < 0:
            raise Exception("Bz2 compressed data was the wrong length")

        o.seek(dst_offset)
        o.write(data)
        padding = dst_length - len(data)
        if padding < 0:
            raise Exception("Wrong length")

        out.write(b'\x00'*padding)

Signatures#

message Signatures {
  message Signature {
    optional uint32 version = 1;
    optional bytes data = 2;
  }
  repeated Signature signatures = 1;
}

Signatures are SHA 256 hashes that have been PKCS1v15 padded and encrypted using the private signing key. The SHA 256 hash is of the update file from magic to the end of the blobs. You can retrieve the SHA 256 hash from the signature by using the public key stored on the device at /usr/share/update_engine/update-payload-key.pub.pem to decrypt it.

The following example python code can be used to retrieve the hash embedded in the signature:

import struct

from cryptography.hazmat.primitives.serialization import load_pem_public_key
from cryptography.hazmat.primitives.asymmetric.padding import PKCS1v15
from cryptography.hazmat.primitives.hashes import SHA256

# This file will need to be generated from
# update_metadata.proto
from .update_metadata_pb2 import DeltaArchiveManifest

with open("update.signed", 'rb') as f:
    if f.read(4) != b"CrAU":
        raise Exception("Wrong header")

    major = struct.unpack(">Q", f.read(8))[0]
    if major != 1:
        raise Exception("Unsupported version")

    size = struct.unpack(">Q", f.read(8))[0]
    data = f.read(size)
    manifest = DeltaArchiveManifest.FromString(data)
    f.seek(manifest.signatures_offset)
    data = f.read(manifest.signatures_size)
    signatures = Signatures.FromString(data)
    for signature in signatures.signatures:
        if signature.version == 2:
            break;

    if signature.version != 2:
        raise Exception("Unsupported signature version")

with open("update-payload-key.pub.pem", 'rb') as f:
    publickey = load_pem_public_key(f)

publickey.recover_data_from_signature(
    signature.data,
    PKCS1v15(),
    SHA256
)

InstallProcedure#

This appears to be unused

message InstallInfo {
  optional uint64 size = 1;
  optional bytes hash = 2;
}

message InstallProcedure {
  enum Type {
    KERNEL = 0;
  }
  optional Type type = 1;
  repeated InstallOperation operations = 2;
  optional InstallInfo old_info = 3;
  optional InstallInfo new_info = 4;
}
This site was last updated on Dec 15, 2024.