blob: 3a58755e47df4ffd1020248761ab40107fe1a73f [file] [log] [blame]
#!/usr/bin/env python
# Copyright (C) 2018 The Android Open Source Project
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.
from __future__ import print_function
import logging
import os.path
import shlex
import struct
import common
import sparse_img
from rangelib import RangeSet
logger = logging.getLogger(__name__)
FIXED_SALT = "aee087a5be3b982978c923f566a94613496b417f2af592639bc80d141e34dfe7"
class BuildVerityImageError(Exception):
"""An Exception raised during verity image building."""
def __init__(self, message):
Exception.__init__(self, message)
def GetVerityFECSize(image_size):
cmd = ["fec", "-s", str(image_size)]
output = common.RunAndCheckOutput(cmd, verbose=False)
return int(output)
def GetVerityTreeSize(image_size):
cmd = ["build_verity_tree", "-s", str(image_size)]
output = common.RunAndCheckOutput(cmd, verbose=False)
return int(output)
def GetVerityMetadataSize(image_size):
cmd = ["", "size", str(image_size)]
output = common.RunAndCheckOutput(cmd, verbose=False)
return int(output)
def GetVeritySize(image_size, fec_supported):
verity_tree_size = GetVerityTreeSize(image_size)
verity_metadata_size = GetVerityMetadataSize(image_size)
verity_size = verity_tree_size + verity_metadata_size
if fec_supported:
fec_size = GetVerityFECSize(image_size + verity_size)
return verity_size + fec_size
return verity_size
def GetSimgSize(image_file):
simg = sparse_img.SparseImage(image_file, build_map=False)
return simg.blocksize * simg.total_blocks
def ZeroPadSimg(image_file, pad_size):
blocks = pad_size // BLOCK_SIZE"Padding %d blocks (%d bytes)", blocks, pad_size)
simg = sparse_img.SparseImage(image_file, mode="r+b", build_map=False)
simg.AppendFillChunk(0, blocks)
def BuildVerityFEC(sparse_image_path, verity_path, verity_fec_path,
cmd = ["fec", "-e", "-p", str(padding_size), sparse_image_path,
verity_path, verity_fec_path]
def BuildVerityTree(sparse_image_path, verity_image_path):
cmd = ["build_verity_tree", "-A", FIXED_SALT, sparse_image_path,
output = common.RunAndCheckOutput(cmd)
root, salt = output.split()
return root, salt
def BuildVerityMetadata(image_size, verity_metadata_path, root_hash, salt,
block_device, signer_path, key, signer_args,
cmd = ["", "build", str(image_size),
verity_metadata_path, root_hash, salt, block_device, signer_path, key]
if signer_args:
cmd.append("--signer_args=\"%s\"" % (' '.join(signer_args),))
if verity_disable:
def Append2Simg(sparse_image_path, unsparse_image_path, error_message):
"""Appends the unsparse image to the given sparse image.
sparse_image_path: the path to the (sparse) image
unsparse_image_path: the path to the (unsparse) image
BuildVerityImageError: On error.
cmd = ["append2simg", sparse_image_path, unsparse_image_path]
raise BuildVerityImageError(error_message)
def Append(target, file_to_append, error_message):
"""Appends file_to_append to target.
BuildVerityImageError: On error.
with open(target, "a") as out_file, open(file_to_append, "r") as input_file:
for line in input_file:
except IOError:
raise BuildVerityImageError(error_message)
def CreateVerityImageBuilder(prop_dict):
"""Returns a verity image builder based on the given build properties.
prop_dict: A dict that contains the build properties. In particular, it will
look for verity-related property values.
A VerityImageBuilder instance for Verified Boot 1.0 or Verified Boot 2.0; or
None if the given build doesn't support Verified Boot.
partition_size = prop_dict.get("partition_size")
# partition_size could be None at this point, if using dynamic partitions.
if partition_size:
partition_size = int(partition_size)
# Verified Boot 1.0
verity_supported = prop_dict.get("verity") == "true"
is_verity_partition = "verity_block_device" in prop_dict
if verity_supported and is_verity_partition:
if OPTIONS.verity_signer_path is not None:
signer_path = OPTIONS.verity_signer_path
signer_path = prop_dict["verity_signer_cmd"]
return Version1VerityImageBuilder(
prop_dict.get("verity_fec") == "true",
prop_dict["verity_key"] + ".pk8",
"verity_disable" in prop_dict)
# Verified Boot 2.0
if (prop_dict.get("avb_hash_enable") == "true" or
prop_dict.get("avb_hashtree_enable") == "true"):
# key_path and algorithm are only available when chain partition is used.
key_path = prop_dict.get("avb_key_path")
algorithm = prop_dict.get("avb_algorithm")
if prop_dict.get("avb_hash_enable") == "true":
return VerifiedBootVersion2VerityImageBuilder(
return VerifiedBootVersion2VerityImageBuilder(
return None
class VerityImageBuilder(object):
"""A builder that generates an image with verity metadata for Verified Boot.
A VerityImageBuilder instance handles the works for building an image with
verity metadata for supporting Android Verified Boot. This class defines the
common interface between Verified Boot 1.0 and Verified Boot 2.0. A matching
builder will be returned based on the given build properties.
More info on the verity image generation can be found at the following link.
def CalculateMaxImageSize(self, partition_size):
"""Calculates the filesystem image size for the given partition size."""
raise NotImplementedError
def CalculateDynamicPartitionSize(self, image_size):
"""Calculates and sets the partition size for a dynamic partition."""
raise NotImplementedError
def PadSparseImage(self, out_file):
"""Adds padding to the generated sparse image."""
raise NotImplementedError
def Build(self, out_file):
"""Builds the verity image and writes it to the given file."""
raise NotImplementedError
class Version1VerityImageBuilder(VerityImageBuilder):
"""A VerityImageBuilder for Verified Boot 1.0."""
def __init__(self, partition_size, block_dev, fec_supported, signer_path,
signer_key, signer_args, verity_disable):
self.version = 1
self.partition_size = partition_size
self.block_device = block_dev
self.fec_supported = fec_supported
self.signer_path = signer_path
self.signer_key = signer_key
self.signer_args = signer_args
self.verity_disable = verity_disable
self.image_size = None
self.verity_size = None
def CalculateDynamicPartitionSize(self, image_size):
# This needs to be implemented. Note that returning the given image size as
# the partition size doesn't make sense, as it will fail later.
raise NotImplementedError
def CalculateMaxImageSize(self, partition_size=None):
"""Calculates the max image size by accounting for the verity metadata.
partition_size: The partition size, which defaults to self.partition_size
if unspecified.
The size of the image adjusted for verity metadata.
if partition_size is None:
partition_size = self.partition_size
assert partition_size > 0, \
"Invalid partition size: {}".format(partition_size)
hi = partition_size
if hi % BLOCK_SIZE != 0:
hi = (hi // BLOCK_SIZE) * BLOCK_SIZE
# verity tree and fec sizes depend on the partition size, which
# means this estimate is always going to be unnecessarily small
verity_size = GetVeritySize(hi, self.fec_supported)
lo = partition_size - verity_size
result = lo
# do a binary search for the optimal size
while lo < hi:
i = ((lo + hi) // (2 * BLOCK_SIZE)) * BLOCK_SIZE
v = GetVeritySize(i, self.fec_supported)
if i + v <= partition_size:
if result < i:
result = i
verity_size = v
lo = i + BLOCK_SIZE
hi = i
self.image_size = result
self.verity_size = verity_size
"Calculated image size for verity: partition_size %d, image_size %d, "
"verity_size %d", partition_size, result, verity_size)
return result
def Build(self, out_file):
"""Creates an image that is verifiable using dm-verity.
out_file: the output image.
AssertionError: On invalid partition sizes.
BuildVerityImageError: On other errors.
image_size = int(self.image_size)
tempdir_name = common.MakeTempDir(suffix="_verity_images")
# Get partial image paths.
verity_image_path = os.path.join(tempdir_name, "verity.img")
verity_metadata_path = os.path.join(tempdir_name, "verity_metadata.img")
# Build the verity tree and get the root hash and salt.
root_hash, salt = BuildVerityTree(out_file, verity_image_path)
# Build the metadata blocks.
image_size, verity_metadata_path, root_hash, salt, self.block_device,
self.signer_path, self.signer_key, self.signer_args,
padding_size = self.partition_size - self.image_size - self.verity_size
assert padding_size >= 0
# Build the full verified image.
verity_image_path, verity_metadata_path,
"Failed to append verity metadata")
if self.fec_supported:
# Build FEC for the entire partition, including metadata.
verity_fec_path = os.path.join(tempdir_name, "verity_fec.img")
out_file, verity_image_path, verity_fec_path, padding_size)
Append(verity_image_path, verity_fec_path, "Failed to append FEC")
out_file, verity_image_path, "Failed to append verity data")
def PadSparseImage(self, out_file):
sparse_image_size = GetSimgSize(out_file)
if sparse_image_size > self.image_size:
raise BuildVerityImageError(
"Error: image size of {} is larger than partition size of "
"{}".format(sparse_image_size, self.image_size))
ZeroPadSimg(out_file, self.image_size - sparse_image_size)
class VerifiedBootVersion2VerityImageBuilder(VerityImageBuilder):
"""A VerityImageBuilder for Verified Boot 2.0."""
def __init__(self, partition_name, partition_size, footer_type, avbtool,
key_path, algorithm, salt, signing_args):
self.version = 2
self.partition_name = partition_name
self.partition_size = partition_size
self.footer_type = footer_type
self.avbtool = avbtool
self.algorithm = algorithm
self.key_path = key_path
self.salt = salt
self.signing_args = signing_args
self.image_size = None
def CalculateMinPartitionSize(self, image_size, size_calculator=None):
"""Calculates min partition size for a given image size.
This is used when determining the partition size for a dynamic partition,
which should be cover the given image size (for filesystem files) as well as
the verity metadata size.
image_size: The size of the image in question.
size_calculator: The function to calculate max image size
for a given partition size.
The minimum partition size required to accommodate the image size.
if size_calculator is None:
size_calculator = self.CalculateMaxImageSize
# Use image size as partition size to approximate final partition size.
image_ratio = size_calculator(image_size) / float(image_size)
# Prepare a binary search for the optimal partition size.
lo = int(image_size / image_ratio) // BLOCK_SIZE * BLOCK_SIZE - BLOCK_SIZE
# Ensure lo is small enough: max_image_size should <= image_size.
delta = BLOCK_SIZE
max_image_size = size_calculator(lo)
while max_image_size > image_size:
image_ratio = max_image_size / float(lo)
lo = int(image_size / image_ratio) // BLOCK_SIZE * BLOCK_SIZE - delta
delta *= 2
max_image_size = size_calculator(lo)
hi = lo + BLOCK_SIZE
# Ensure hi is large enough: max_image_size should >= image_size.
delta = BLOCK_SIZE
max_image_size = size_calculator(hi)
while max_image_size < image_size:
image_ratio = max_image_size / float(hi)
hi = int(image_size / image_ratio) // BLOCK_SIZE * BLOCK_SIZE + delta
delta *= 2
max_image_size = size_calculator(hi)
partition_size = hi
# Start to binary search.
while lo < hi:
mid = ((lo + hi) // (2 * BLOCK_SIZE)) * BLOCK_SIZE
max_image_size = size_calculator(mid)
if max_image_size >= image_size: # if mid can accommodate image_size
if mid < partition_size: # if a smaller partition size is found
partition_size = mid
hi = mid
lo = mid + BLOCK_SIZE
"CalculateMinPartitionSize(%d): partition_size %d.", image_size,
return partition_size
def CalculateDynamicPartitionSize(self, image_size):
self.partition_size = self.CalculateMinPartitionSize(image_size)
return self.partition_size
def CalculateMaxImageSize(self, partition_size=None):
"""Calculates max image size for a given partition size.
partition_size: The partition size, which defaults to self.partition_size
if unspecified.
The maximum image size.
BuildVerityImageError: On error or getting invalid image size.
if partition_size is None:
partition_size = self.partition_size
assert partition_size > 0, \
"Invalid partition size: {}".format(partition_size)
add_footer = ("add_hash_footer" if self.footer_type == self.AVB_HASH_FOOTER
else "add_hashtree_footer")
cmd = [self.avbtool, add_footer, "--partition_size",
str(partition_size), "--calc_max_image_size"]
proc = common.Run(cmd)
output, _ = proc.communicate()
if proc.returncode != 0:
raise BuildVerityImageError(
"Failed to calculate max image size:\n{}".format(output))
image_size = int(output)
if image_size <= 0:
raise BuildVerityImageError(
"Invalid max image size: {}".format(output))
self.image_size = image_size
return image_size
def PadSparseImage(self, out_file):
# No-op as the padding is taken care of by avbtool.
def Build(self, out_file):
"""Adds dm-verity hashtree and AVB metadata to an image.
out_file: Path to image to modify.
add_footer = ("add_hash_footer" if self.footer_type == self.AVB_HASH_FOOTER
else "add_hashtree_footer")
cmd = [self.avbtool, add_footer,
"--partition_size", str(self.partition_size),
"--partition_name", self.partition_name,
"--image", out_file]
if self.key_path and self.algorithm:
cmd.extend(["--key", self.key_path, "--algorithm", self.algorithm])
if self.salt:
cmd.extend(["--salt", self.salt])
proc = common.Run(cmd)
output, _ = proc.communicate()
if proc.returncode != 0:
raise BuildVerityImageError("Failed to add AVB footer: {}".format(output))
class HashtreeInfoGenerationError(Exception):
"""An Exception raised during hashtree info generation."""
def __init__(self, message):
Exception.__init__(self, message)
class HashtreeInfo(object):
def __init__(self):
self.hashtree_range = None
self.filesystem_range = None
self.hash_algorithm = None
self.salt = None
self.root_hash = None
def CreateHashtreeInfoGenerator(partition_name, block_size, info_dict):
generator = None
if (info_dict.get("verity") == "true" and
partition_size = info_dict["{}_size".format(partition_name)]
fec_supported = info_dict.get("verity_fec") == "true"
generator = VerifiedBootVersion1HashtreeInfoGenerator(
partition_size, block_size, fec_supported)
return generator
class HashtreeInfoGenerator(object):
def Generate(self, image):
raise NotImplementedError
def DecomposeSparseImage(self, image):
raise NotImplementedError
def ValidateHashtree(self):
raise NotImplementedError
class VerifiedBootVersion1HashtreeInfoGenerator(HashtreeInfoGenerator):
"""A class that parses the metadata of hashtree for a given partition."""
def __init__(self, partition_size, block_size, fec_supported):
"""Initialize VerityTreeInfo with the sparse image and input property.
partition_size: The whole size in bytes of a partition, including the
filesystem size, padding size, and verity size.
block_size: Expected size in bytes of each block for the sparse image.
fec_supported: True if the verity section contains fec data.
self.block_size = block_size
self.partition_size = partition_size
self.fec_supported = fec_supported
self.image = None
self.filesystem_size = None
self.hashtree_size = None
self.metadata_size = None
prop_dict = {
'partition_size': str(partition_size),
'verity': 'true',
'verity_fec': 'true' if fec_supported else None,
# 'verity_block_device' needs to be present to indicate a verity-enabled
# partition.
'verity_block_device': '',
# We don't need the following properties that are needed for signing the
# verity metadata.
'verity_key': '',
'verity_signer_cmd': None,
self.verity_image_builder = CreateVerityImageBuilder(prop_dict)
self.hashtree_info = HashtreeInfo()
def DecomposeSparseImage(self, image):
"""Calculate the verity size based on the size of the input image.
Since we already know the structure of a verity enabled image to be:
[filesystem, verity_hashtree, verity_metadata, fec_data]. We can then
calculate the size and offset of each section.
self.image = image
assert self.block_size == image.blocksize
assert self.partition_size == image.total_blocks * self.block_size, \
"partition size {} doesn't match with the calculated image size." \
" total_blocks: {}".format(self.partition_size, image.total_blocks)
adjusted_size = self.verity_image_builder.CalculateMaxImageSize()
assert adjusted_size % self.block_size == 0
verity_tree_size = GetVerityTreeSize(adjusted_size)
assert verity_tree_size % self.block_size == 0
metadata_size = GetVerityMetadataSize(adjusted_size)
assert metadata_size % self.block_size == 0
self.filesystem_size = adjusted_size
self.hashtree_size = verity_tree_size
self.metadata_size = metadata_size
self.hashtree_info.filesystem_range = RangeSet(
data=[0, adjusted_size / self.block_size])
self.hashtree_info.hashtree_range = RangeSet(
data=[adjusted_size / self.block_size,
(adjusted_size + verity_tree_size) / self.block_size])
def _ParseHashtreeMetadata(self):
"""Parses the hash_algorithm, root_hash, salt from the metadata block."""
metadata_start = self.filesystem_size + self.hashtree_size
metadata_range = RangeSet(
data=[metadata_start / self.block_size,
(metadata_start + self.metadata_size) / self.block_size])
meta_data = ''.join(self.image.ReadRangeSet(metadata_range))
# More info about the metadata structure available in:
# system/extras/verity/
header_bin = meta_data[0:META_HEADER_SIZE]
header = struct.unpack("II256sI", header_bin)
# header: magic_number, version, signature, table_len
assert header[0] == 0xb001b001, header[0]
table_len = header[3]
verity_table = meta_data[META_HEADER_SIZE: META_HEADER_SIZE + table_len]
table_entries = verity_table.rstrip().split()
# Expected verity table format: "1 block_device block_device block_size
# block_size data_blocks data_blocks hash_algorithm root_hash salt"
assert len(table_entries) == 10, "Unexpected verity table size {}".format(
assert (int(table_entries[3]) == self.block_size and
int(table_entries[4]) == self.block_size)
assert (int(table_entries[5]) * self.block_size == self.filesystem_size and
int(table_entries[6]) * self.block_size == self.filesystem_size)
self.hashtree_info.hash_algorithm = table_entries[7]
self.hashtree_info.root_hash = table_entries[8]
self.hashtree_info.salt = table_entries[9]
def ValidateHashtree(self):
"""Checks that we can reconstruct the verity hash tree."""
# Writes the filesystem section to a temp file; and calls the executable
# build_verity_tree to construct the hash tree.
adjusted_partition = common.MakeTempFile(prefix="adjusted_partition")
with open(adjusted_partition, "wb") as fd:
self.image.WriteRangeDataToFd(self.hashtree_info.filesystem_range, fd)
generated_verity_tree = common.MakeTempFile(prefix="verity")
root_hash, salt = BuildVerityTree(adjusted_partition, generated_verity_tree)
# The salt should be always identical, as we use fixed value.
assert salt == self.hashtree_info.salt, \
"Calculated salt {} doesn't match the one in metadata {}".format(
salt, self.hashtree_info.salt)
if root_hash != self.hashtree_info.root_hash:
"Calculated root hash %s doesn't match the one in metadata %s",
root_hash, self.hashtree_info.root_hash)
return False
# Reads the generated hash tree and checks if it has the exact same bytes
# as the one in the sparse image.
with open(generated_verity_tree, "rb") as fd:
return == ''.join(self.image.ReadRangeSet(
def Generate(self, image):
"""Parses and validates the hashtree info in a sparse image.
hashtree_info: The information needed to reconstruct the hashtree.
HashtreeInfoGenerationError: If we fail to generate the exact bytes of
the hashtree.
if not self.ValidateHashtree():
raise HashtreeInfoGenerationError("Failed to reconstruct the verity tree")
return self.hashtree_info