mirror of https://github.com/ARMmbed/mbed-os.git
268 lines
9.2 KiB
Python
268 lines
9.2 KiB
Python
# Copyright 2017 Linaro Limited
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# Copyright (c) 2018-2019, Arm Limited.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""
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Image signing and management.
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"""
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from . import version as versmod
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from . import boot_record as br
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import hashlib
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import struct
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IMAGE_MAGIC = 0x96f3b83d
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IMAGE_HEADER_SIZE = 32
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TLV_HEADER_SIZE = 4
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PAYLOAD_DIGEST_SIZE = 32 # SHA256 hash
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KEYHASH_SIZE = 32
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DEP_IMAGES_KEY = "images"
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DEP_VERSIONS_KEY = "versions"
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# Image header flags.
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IMAGE_F = {
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'PIC': 0x0000001,
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'NON_BOOTABLE': 0x0000010,
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'RAM_LOAD': 0x0000020, }
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TLV_VALUES = {
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'KEYHASH': 0x01,
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'KEY' : 0x02,
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'SHA256' : 0x10,
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'RSA2048': 0x20,
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'RSA3072': 0x23,
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'DEPENDENCY': 0x40,
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'SEC_CNT': 0x50,
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'BOOT_RECORD': 0x60, }
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TLV_INFO_SIZE = 4
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TLV_INFO_MAGIC = 0x6907
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TLV_PROT_INFO_MAGIC = 0x6908
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# Sizes of the image trailer, depending on flash write size.
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trailer_sizes = {
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write_size: 128 * 3 * write_size + 8 * 2 + 16
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for write_size in [1, 2, 4, 8]
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}
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boot_magic = bytearray([
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0x77, 0xc2, 0x95, 0xf3,
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0x60, 0xd2, 0xef, 0x7f,
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0x35, 0x52, 0x50, 0x0f,
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0x2c, 0xb6, 0x79, 0x80, ])
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class TLV():
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def __init__(self, magic=TLV_INFO_MAGIC):
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self.magic = magic
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self.buf = bytearray()
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def __len__(self):
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return TLV_INFO_SIZE + len(self.buf)
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def add(self, kind, payload):
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"""
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Add a TLV record. Kind should be a string found in TLV_VALUES above.
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"""
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buf = struct.pack('<BBH', TLV_VALUES[kind], 0, len(payload))
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self.buf += buf
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self.buf += payload
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def get(self):
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if len(self.buf) == 0:
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return bytes()
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header = struct.pack('<HH', self.magic, len(self))
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return header + bytes(self.buf)
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class Image():
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@classmethod
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def load(cls, path, included_header=False, **kwargs):
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"""Load an image from a given file"""
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with open(path, 'rb') as f:
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payload = f.read()
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obj = cls(**kwargs)
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obj.payload = payload
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# Add the image header if needed.
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if not included_header and obj.header_size > 0:
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obj.payload = (b'\000' * obj.header_size) + obj.payload
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obj.check()
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return obj
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def __init__(self, version, header_size=IMAGE_HEADER_SIZE, security_cnt=0,
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pad=0):
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self.version = version
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self.header_size = header_size or IMAGE_HEADER_SIZE
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self.security_cnt = security_cnt
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self.pad = pad
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def __repr__(self):
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return "<Image version={}, header_size={}, security_counter={}, \
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pad={}, payloadlen=0x{:x}>".format(
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self.version,
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self.header_size,
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self.security_cnt,
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self.pad,
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len(self.payload))
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def save(self, path):
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with open(path, 'wb') as f:
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f.write(self.payload)
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def check(self):
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"""Perform some sanity checking of the image."""
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# If there is a header requested, make sure that the image
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# starts with all zeros.
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if self.header_size > 0:
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if any(v != 0 and v != b'\000' for v in self.payload[0:self.header_size]):
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raise Exception("Padding requested, but image does not start with zeros")
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def sign(self, sw_type, key, ramLoadAddress, dependencies=None):
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image_version = (str(self.version.major) + '.'
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+ str(self.version.minor) + '.'
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+ str(self.version.revision))
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# Calculate the hash of the public key
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if key is not None:
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pub = key.get_public_bytes()
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sha = hashlib.sha256()
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sha.update(pub)
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pubbytes = sha.digest()
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else:
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pubbytes = bytes(KEYHASH_SIZE)
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# The image hash is computed over the image header, the image itself
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# and the protected TLV area. However, the boot record TLV (which is
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# part of the protected area) should contain this hash before it is
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# even calculated. For this reason the script fills this field with
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# zeros and the bootloader will insert the right value later.
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image_hash = bytes(PAYLOAD_DIGEST_SIZE)
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# Create CBOR encoded boot record
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boot_record = br.create_sw_component_data(sw_type, image_version,
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"SHA256", image_hash,
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pubbytes)
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# Mandatory protected TLV area: TLV info header
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# + security counter TLV
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# + boot record TLV
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# Size of the security counter TLV: header ('BBH') + payload ('I')
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# = 8 Bytes
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protected_tlv_size = TLV_INFO_SIZE + 8 + TLV_HEADER_SIZE \
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+ len(boot_record)
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if dependencies is None:
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dependencies_num = 0
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else:
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# Size of a dependency TLV:
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# header ('BBH') + payload('IBBHI') = 16 Bytes
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dependencies_num = len(dependencies[DEP_IMAGES_KEY])
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protected_tlv_size += (dependencies_num * 16)
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# At this point the image is already on the payload, this adds
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# the header to the payload as well
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self.add_header(key, protected_tlv_size, ramLoadAddress)
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prot_tlv = TLV(TLV_PROT_INFO_MAGIC)
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# Protected TLVs must be added first, because they are also included
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# in the hash calculation
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payload = struct.pack('I', self.security_cnt)
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prot_tlv.add('SEC_CNT', payload)
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prot_tlv.add('BOOT_RECORD', boot_record)
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if dependencies_num != 0:
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for i in range(dependencies_num):
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payload = struct.pack(
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'<'+'B3x'+'BBHI',
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int(dependencies[DEP_IMAGES_KEY][i]),
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dependencies[DEP_VERSIONS_KEY][i].major,
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dependencies[DEP_VERSIONS_KEY][i].minor,
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dependencies[DEP_VERSIONS_KEY][i].revision,
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dependencies[DEP_VERSIONS_KEY][i].build
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)
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prot_tlv.add('DEPENDENCY', payload)
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self.payload += prot_tlv.get()
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sha = hashlib.sha256()
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sha.update(self.payload)
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image_hash = sha.digest()
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tlv = TLV()
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tlv.add('SHA256', image_hash)
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if key is not None:
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if key.get_public_key_format() == 'hash':
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tlv.add('KEYHASH', pubbytes)
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else:
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tlv.add('KEY', pub)
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sig = key.sign(self.payload)
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tlv.add(key.sig_tlv(), sig)
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self.payload += tlv.get()
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def add_header(self, key, protected_tlv_size, ramLoadAddress):
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"""Install the image header.
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The key is needed to know the type of signature, and
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approximate the size of the signature."""
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flags = 0
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if ramLoadAddress is not None:
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# add the load address flag to the header to indicate that an SRAM
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# load address macro has been defined
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flags |= IMAGE_F["RAM_LOAD"]
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fmt = ('<' +
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# type ImageHdr struct {
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'I' + # Magic uint32
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'I' + # LoadAddr uint32
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'H' + # HdrSz uint16
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'H' + # PTLVSz uint16
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'I' + # ImgSz uint32
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'I' + # Flags uint32
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'BBHI' + # Vers ImageVersion
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'I' # Pad1 uint32
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) # }
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assert struct.calcsize(fmt) == IMAGE_HEADER_SIZE
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header = struct.pack(fmt,
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IMAGE_MAGIC,
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0 if (ramLoadAddress is None) else ramLoadAddress, # LoadAddr
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self.header_size,
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protected_tlv_size, # TLV info header + Protected TLVs
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len(self.payload) - self.header_size, # ImageSz
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flags,
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self.version.major,
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self.version.minor or 0,
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self.version.revision or 0,
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self.version.build or 0,
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0) # Pad1
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self.payload = bytearray(self.payload)
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self.payload[:len(header)] = header
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def pad_to(self, size, align):
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"""Pad the image to the given size, with the given flash alignment."""
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tsize = trailer_sizes[align]
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padding = size - (len(self.payload) + tsize)
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if padding < 0:
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msg = "Image size (0x{:x}) + trailer (0x{:x}) exceeds requested size 0x{:x}".format(
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len(self.payload), tsize, size)
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raise Exception(msg)
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pbytes = b'\xff' * padding
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pbytes += b'\xff' * (tsize - len(boot_magic))
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pbytes += boot_magic
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self.payload += pbytes
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