imgtool: Fix custom TLV encoding

Encode custom TLV of integer type according to image's byteorder.

Signed-off-by: Rustam Ismayilov <rustam.ismayilov@arm.com>
Change-Id: If5028e57473a66cf9be61c770f45d3c1e32d9632

Author: rustammendel

scripts/imgtool/main.py

@@ -17,16 +17,18 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import base64
+import getpass
 import re
+import sys
+
 import click
-import getpass
+
 import imgtool.keys as keys
-import sys
-import base64
 from imgtool import image, imgtool_version
+from imgtool.dumpinfo import dump_imginfo
 from imgtool.keys.general import key_types_matching
 from imgtool.version import decode_version
-from imgtool.dumpinfo import dump_imginfo
 from .keys import (
     RSAUsageError, ECDSAUsageError, Ed25519UsageError, X25519UsageError)
 
@@ -455,7 +457,10 @@ def sign(key, public_key_format, align, version, pad_sig, header_size,
         if value.startswith('0x'):
             if len(value[2:]) % 2:
                 raise click.UsageError('Custom TLV length is odd.')
-            custom_tlvs[tag] = bytes.fromhex(value[2:])
+            ctlv_ba = bytearray.fromhex(value[2:])
+            # encode integer TLVs as per byteorder
+            ctlv_ba.reverse() if endian == "little" else None
+            custom_tlvs[tag] = ctlv_ba
         else:
             custom_tlvs[tag] = value.encode('utf-8')