tools: Preliminary tool support for signed-boot on 2712

Update rpi-eeprom-config to support replacement of bootcode.bin
with a customer counter-signed version.

Add a new rpi-sign-bootcode script which enables bootcode.bin
to be counter-signed with the customer key.

N.B. Signed boot on 2712 requires newer firmware which is currently
under development and has not been released.

rpi-eeprom-config

@@ -20,6 +20,7 @@ BOOTCONF_TXT = 'bootconf.txt'
 BOOTCONF_SIG = 'bootconf.sig'
 PUBKEY_BIN = 'pubkey.bin'
 CACERT_DER = 'cacert.der'
+BOOTCODE_BIN = 'bootcode.bin'
 
 # Each section starts with a magic number followed by a 32 bit offset to the
 # next section (big-endian).
@@ -297,14 +298,22 @@ class BootloaderImage(object):
         length = -1
         is_last = False
 
-        next_offset = self._image_size - ERASE_ALIGN_SIZE # Don't create padding inside the bootloader scratch page
+        if filename == BOOTCODE_BIN:
-        for i in range(0, len(self._sections)):
+            next_offset = 0
+            dst_filename = filename
+            i = 0
             s = self._sections[i]
-            if s.magic == FILE_MAGIC and s.filename == filename:
+            offset = s.offset
-                is_last = (i == len(self._sections) - 1)
+            length = s.length
-                offset = s.offset
+        else:
-                length = s.length
+            next_offset = self._image_size - ERASE_ALIGN_SIZE # Don't create padding inside the bootloader scratch page
-                break
+            for i in range(0, len(self._sections)):
+                s = self._sections[i]
+                if s.magic == FILE_MAGIC and s.filename == filename:
+                    is_last = (i == len(self._sections) - 1)
+                    offset = s.offset
+                    length = s.length
+                    break
 
         # Find the start of the next non padding section
         i += 1
@@ -318,30 +327,43 @@ class BootloaderImage(object):
         debug('%s offset %d length %d is-last %d next %d' % (filename, ret[0], ret[1], ret[2], ret[3]))
         return ret
 
-    def update(self, src_bytes, dst_filename):
+    def update(self, src_bytes, dst_filename, bootcode = False):
         """
         Replaces a modifiable file with specified byte array.
         """
-        hdr_offset, length, is_last, next_offset = self.find_file(dst_filename)
+        if bootcode:
-        update_len = len(src_bytes) + FILE_HDR_LEN
+            hdr_offset, length, is_last, next_offset = self.find_file(dst_filename)
+            struct.pack_into('>L', self._bytes, hdr_offset + 4, len(src_bytes))
+            struct.pack_into(("%ds" % len(src_bytes)), self._bytes, hdr_offset + 8, src_bytes)
+            pad_start = hdr_offset + len(src_bytes) + 8
+            is_last = False
+            debug("bootcode padded to %d" % next_offset);
+            if next_offset < 128 * 1024:
+                raise Exception("update-bootcode: Can't update image - 128K must be reserved for bootcode")
+            if next_offset < 0:
+                raise Exception("update-bootcode: Failed to find next section")
 
-        if hdr_offset + update_len > self._image_size - ERASE_ALIGN_SIZE:
+        else:
-            raise Exception('No space available - image past EOF.')
+            hdr_offset, length, is_last, next_offset = self.find_file(dst_filename)
+            update_len = len(src_bytes) + FILE_HDR_LEN
 
-        if hdr_offset < 0:
+            if hdr_offset + update_len > self._image_size - ERASE_ALIGN_SIZE:
-            raise Exception('Update target %s not found' % dst_filename)
+                raise Exception('No space available - image past EOF.')
 
-        if hdr_offset + update_len > next_offset:
+            if hdr_offset < 0:
-            raise Exception('Update %d bytes is larger than section size %d' % (update_len, next_offset - hdr_offset))
+                raise Exception('Update target %s not found' % dst_filename)
 
-        new_len = len(src_bytes) + FILENAME_LEN + 4
+            if hdr_offset + update_len > next_offset:
-        struct.pack_into('>L', self._bytes, hdr_offset + 4, new_len)
+                raise Exception('Update %d bytes is larger than section size %d' % (update_len, next_offset - hdr_offset))
-        struct.pack_into(("%ds" % len(src_bytes)), self._bytes,
-                         hdr_offset + 4 + FILE_HDR_LEN, src_bytes)
 
-        # If the new file is smaller than the old file then set any old
+            new_len = len(src_bytes) + FILENAME_LEN + 4
-        # data which is now unused to all ones (erase value)
+            struct.pack_into('>L', self._bytes, hdr_offset + 4, new_len)
-        pad_start = hdr_offset + 4 + FILE_HDR_LEN + len(src_bytes)
+            struct.pack_into(("%ds" % len(src_bytes)), self._bytes,
+                             hdr_offset + 4 + FILE_HDR_LEN, src_bytes)
+
+            # If the new file is smaller than the old file then set any old
+            # data which is now unused to all ones (erase value)
+            pad_start = hdr_offset + 4 + FILE_HDR_LEN + len(src_bytes)
 
         # Add padding up to 8-byte boundary
         while pad_start % 8 != 0:
@@ -380,10 +402,11 @@ class BootloaderImage(object):
         Replaces the contents of dst_filename in the EEPROM with the contents of src_file.
         """
         src_bytes = open(src_filename, 'rb').read()
-        if len(src_bytes) > MAX_FILE_SIZE:
+        bootcode = dst_filename == BOOTCODE_BIN
+        if not bootcode and len(src_bytes) > MAX_FILE_SIZE:
             raise Exception("src file %s is too large (%d bytes). The maximum size is %d bytes."
                             % (src_filename, len(src_bytes), MAX_FILE_SIZE))
-        self.update(src_bytes, dst_filename)
+        self.update(src_bytes, dst_filename, bootcode)
 
     def set_timestamp(self, timestamp):
         """
@@ -409,14 +432,22 @@ class BootloaderImage(object):
 
     def get_file(self, filename):
         hdr_offset, length, is_last, next_offset = self.find_file(filename)
-        offset = hdr_offset + 4 + FILE_HDR_LEN
+        if filename == BOOTCODE_BIN:
-        file_bytes = self._bytes[offset:offset+length-FILENAME_LEN-4]
+            offset = hdr_offset + 8
+            file_bytes = self._bytes[offset:offset+length]
+        else:
+            offset = hdr_offset + 4 + FILE_HDR_LEN
+            file_bytes = self._bytes[offset:offset+length-FILENAME_LEN-4]
+
         return file_bytes
 
     def extract_files(self):
         for i in range(0, len(self._sections)):
             s = self._sections[i]
-            if s.magic == FILE_MAGIC:
+            if s.magic == MAGIC and s.offset == 0:
+                file_bytes = self.get_file(BOOTCODE_BIN)
+                open(BOOTCODE_BIN, 'wb').write(file_bytes)
+            elif s.magic == FILE_MAGIC:
                 file_bytes = self.get_file(s.filename)
                 open(s.filename, 'wb').write(file_bytes)
 
@@ -515,6 +546,7 @@ See 'rpi-eeprom-update -h' for more information about the available EEPROM image
     parser.add_argument('-d', '--digest', help='Signed boot only. The name of the .sig file generated by rpi-eeprom-dgst for config.txt ', required=False)
     parser.add_argument('-p', '--pubkey', help='Signed boot only. The name of the RSA public key file to store in the EEPROM', required=False)
     parser.add_argument('-x', '--extract', action='store_true', default=False, help='Extract the modifiable files (boot.conf, pubkey, signature)', required=False)
+    parser.add_argument('-b', '--bootcode', help='Signed boot 2712 only. The name of the customer signed bootcode.bin file to store in the EEPROM', required=False)
     parser.add_argument('-t', '--timestamp', help='Set the timestamp in the EEPROM image file', required=False)
     parser.add_argument('--cacertder', help='The name of a CA Certificate DER encoded file to store in the EEPROM', required=False)
     parser.add_argument('eeprom', nargs='?', help='Name of EEPROM file to use as input')
@@ -539,7 +571,10 @@ See 'rpi-eeprom-update -h' for more information about the available EEPROM image
         image = BootloaderImage(args.eeprom, args.out)
         if args.timestamp is not None:
             image.set_timestamp(args.timestamp)
-        if args.config is not None:
+        if args.bootcode is not None:
+            image.update_file(args.bootcode, BOOTCODE_BIN)
+            image.write()
+        elif args.config is not None:
             if not os.path.exists(args.config):
                 exit_error("config file '%s' not found" % args.config)
             image.update_file(args.config, BOOTCONF_TXT)

tools/rpi-sign-bootcode

@@ -0,0 +1,229 @@
+#!/usr/bin/env python3
+
+import argparse
+import base64
+import struct
+import sys
+
+# python3 -m pip install pycryptodomex
+from Cryptodome.Hash import HMAC, SHA1, SHA256
+from Cryptodome.PublicKey import RSA
+from Cryptodome.Signature import pkcs1_15
+
+_CONFIG = {'DEBUG': False}
+MAX_BIN_SIZE = 110 * 1024
+
+def debug(msg):
+    """
+    Outputs the msg string to stdout if DEBUG is enabled (via -d)
+    """
+    if _CONFIG['DEBUG']:
+        sys.stderr.write(str(msg) + '\n')
+
+class ImageFile:
+    """
+    Signed binary image
+    """
+    def __init__(self, filename, max_size_kb):
+        self._filename = filename
+        self._bytes_written = 0
+        if self._filename is None:
+           self._of = sys.stdout
+        else:
+           self._of = open(self._filename, "wb")
+        self._max_size_kb = max_size_kb
+        self._bytes = bytearray()
+
+        debug("%8s %20s: [%6s] %s" % ('OFFSET', 'TYPE', 'SIZE', 'DESCRIPTION'))
+        debug("")
+
+    def append(self, data):
+        """
+        Appends a blob of binary data to the image
+        """
+        self._bytes.extend(data)
+
+    def append_file(self, source_file):
+        """
+        Appends the binary contents of source_file to the current image. If
+        source_file is None then a base64 encoded blob is read from stdin.
+        """
+        if source_file is None:
+           b64 = ""
+           for l in sys.stdin.readlines():
+              b64 += l
+           file_bytes = base64.b64decode(b64)
+        else:
+           file_bytes = bytearray(open(source_file, 'rb').read())
+        size = len(file_bytes)
+        debug("%08x %20s: [%6d] %s" % (self.pos(), 'FILE', size, source_file))
+        self.append(file_bytes)
+
+    def append_keynum(self, keynum):
+        """
+        Appends a given key number as a 32-bit LE integer.
+        """
+        if (keynum < 0 or keynum > 4) and keynum != 16:
+            raise Exception("Bad key number %d" % keynum)
+        debug("%08x %20s: [%6d] %d" % (self.pos(), "KEYNUM", 4, keynum))
+        self.append(struct.pack('<i', keynum))
+
+    def append_version(self, version):
+        """
+        Appends a version number, 0-32 to avoid firmware rollback, a Raspberry Pi
+        with OTP bit n set will not execute a firmware without bit n set.
+        """
+        if version < 0 or version > 32:
+            raise Exception("Bad version number %d must be between 0-32" % version)
+        debug("%08x %20s: [%6d] %d" % (self.pos(), "VERSION", 4, version))
+        self.append(struct.pack('<i', version))
+
+    def append_length(self):
+        """
+        Appends the current length to the image as a 32-bit LE integer
+        """
+        length = len(self._bytes)
+        debug("%08x %20s: [%6d] %d" % (self.pos(), "LEN", 4, length))
+        self.append(struct.pack('<i', length))
+
+    def append_public_key(self, pem_file):
+        """
+        Converts an RSA public key into the format expected by the ROM
+        and appends it to the image.
+
+        If a private key is passed then only the public key part is extracted.
+        """
+        arr = bytearray()
+        key = RSA.importKey(open(pem_file, 'r').read())
+
+        if key.size_in_bits() != 2048:
+            raise Exception("RSA key size must be 2048")
+
+        # Export N and E in little endian format
+        arr.extend(key.n.to_bytes(256, byteorder='little'))
+        arr.extend(key.e.to_bytes(8, byteorder='little'))
+        debug("%08x %20s: [%6d] %s" % (self.pos(), 'RSA', len(arr), pem_file))
+        self.append(arr)
+
+    def append_rsa_signature(self, digest_alg, private_pem):
+        """
+        Append a RSA 2048 signature of the SHA256 of the data so far
+        """
+        key = RSA.importKey(open(private_pem, 'r').read())
+        if key.size_in_bits() != 2048:
+            raise Exception("RSA key size must be 2048")
+
+        if digest_alg == 'sha256':
+            digest = SHA256.new(self._bytes)
+        elif digest_alg == 'sha1':
+            digest = SHA1.new(self._bytes)
+
+        signature = pkcs1_15.new(key).sign(digest)
+        self.append(signature)
+        debug("%08x %20s: [%6d] digest %s signature %s" % (self.pos(), 'RSA2048 - SHA256', len(signature), digest.hexdigest(), signature.hex()))
+
+    def append_digest(self, digest_alg, hmac_keyfile):
+        """
+        Appends the hash/digest to the image
+        """
+        if hmac_keyfile is not None:
+            hmac_key = str(open(hmac_keyfile, 'r').read()).strip()
+            expected_keylen = 40
+            if len(hmac_key) != expected_keylen:
+                raise Exception("Bad key length %d expected %d" % (len(hmac_key), expected_keylen))
+
+        if digest_alg == 'hmac-sha256':
+            digest = HMAC.new(base64.b16decode(hmac_key, True), self._bytes, digestmod=SHA256)
+        elif digest_alg == 'hmac-sha1':
+            digest = HMAC.new(base64.b16decode(hmac_key, True), self._bytes, digestmod=SHA1)
+        elif digest_alg == 'sha256':
+            digest = SHA256.new(self._bytes)
+        elif digest_alg == 'sha1':
+            digest = SHA1.new(self._bytes)
+        else:
+            raise Exception("Digest not supported %s" % (digest_alg))
+
+        debug("%08x %20s: [%6d] %s" % (self.pos(), digest_alg, len(digest.digest()), digest.hexdigest()))
+        self.append(digest.digest())
+
+    def pos(self):
+        return len(self._bytes)
+
+    def write(self):
+        if len(self._bytes) > self._max_size_kb:
+            raise Exception("Signed binary size %d is too large. Max size %d" % (len(self._bytes), MAX_BIN_SIZE))
+        debug("Image size %d" % len(self._bytes))
+        if self._filename is None:
+           self._of.buffer.write(base64.b64encode(self._bytes))
+        else:
+           self._of.write(self._bytes)
+
+    def close(self):
+        self._of.close()
+
+def create_2711_image(output, bootcode, private_key, private_keynum, hmac):
+    """
+    Create a 2711 C0 secure-boot compatible seconds stage signed binary.
+    """
+    image = ImageFile(output, MAX_BIN_SIZE)
+    image.append_file(bootcode)
+    image.append_length()
+    image.append_keynum(private_keynum)
+    image.append_rsa_signature('sha1', private_key)
+    image.append_digest('hmac-sha1', hmac)
+    image.write()
+    image.close()
+
+def create_2712_image(output, bootcode, private_key, private_keynum, private_version):
+    """
+    Create 2712 signed bootloader. The HMAC is removed and the full public key is appended.
+    """
+    image = ImageFile(output, MAX_BIN_SIZE)
+    image.append_file(bootcode)
+    image.append_length()
+    image.append_keynum(private_keynum)
+    image.append_version(private_version)
+    image.append_rsa_signature('sha256', private_key)
+    image.append_public_key(private_key)
+    image.write()
+    image.close()
+
+def main():
+    help_text = """
+    Signs a second stage bootloader image.
+
+    Examples:
+        2711 mode:
+        rpi-sign-bootcode --debug -c 2711 -i bootcode.bin.clr -o bootcode.bin -k 2711_rsa_priv_0.pem -n 0 -m bootcode-production.key
+
+        2712 C1 and D0 mode:
+          * HMAC not included on 2712
+          * RSA public key included - ROM just contains the hashes of the RPi public keys.
+
+        Customer counter-signed signed:
+          * Exactly the same as Raspberry Pi signing but the input is the Raspberry Pi signed bootcode.bin
+          * The key number will probably always be 16 to indicate a customer signing
+
+        rpi-sign-bootcode --debug -c 2712 -i bootcode.bin.sign2 -o bootcode.bin -k customer.pem
+    """
+    parser = argparse.ArgumentParser(help_text)
+    parser.add_argument('-o', '--output', required=False, help='Output filename . If not specified the signed images is written to stdout in base64 format')
+    parser.add_argument('-c', '--chip', required=True, type=int, help='Chip number')
+    parser.add_argument('-i', '--input', required=False, help='Path of the unsigned bootcode.bin file OR RPi signed bootcode file sign with the customer key. If NULLL the binary is read from stdin in base64 format')
+    parser.add_argument('-m', '--hmac', required=False, help='Path of the HMAC key file')
+    parser.add_argument('-k', '--private-key', dest='private_key', required=True, help='Path of RSA private key (PEM format)')
+    parser.add_argument('-n', '--private-keynum', dest='private_keynum', required=False, default=0, type=int, help='ROM key index for RPi signing stage')
+    parser.add_argument('-d', '--debug', action='store_true')
+    parser.add_argument('-v', '--private-version', dest='private_version', required=True, type=int, help='Version of firmware, stops firmware rollback, only valid 0-31')
+
+    args = parser.parse_args()
+    _CONFIG['DEBUG'] = args.debug
+    if args.chip == 2711:
+        if args.hmac is None:
+            raise Exception("HMAC key requried for 2711")
+        create_2711_image(args.output, args.input, args.private_key, args.private_keynum, args.hmac)
+    elif args.chip == 2712:
+        create_2712_image(args.output, args.input, args.private_key, args.private_keynum, args.private_version)
+
+if __name__ == '__main__':
+    main()