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Miscellaneous

This repository contains stuff which would be helpful for jailbroken iOS development.

fixobjc2.idc

This is a script to simply studying of Mach-O files on ARM architecture using Objective-C ABI 2.0 for IDA Pro 5.5 and above. Currently, the script mainly does the following:

  • Add comments to all selectors so it becomes clear which selector _objc_msgSend is using.

  • Check all Objective-C methods and create functions for them. This is particularly useful for files with symbols stripped because IDA Pro usually can't recognize those functions as code.

  • Add name to all ivars and classes.

dyld_decache

Starting from iPhone OS 3.1, the individual libraries files supplied by the system are smashed together into a giant cache file (dyld_shared_cache_armvX) to improve performance. This makes development difficult when one only has the IPSW but not the SDK (e.g. Apple TV 2G), because there is no file to link to or reverse engineer.

dyldcache.cc, originally written by D. Howett, was created to unpack files from the dyld_shared_cache_armvX file. Unfortunately, this tool does not try to untangle the interconnection between libraries in the cache, so each extracted file is over 20 MiB in size (as the whole __LINKEDIT segment is duplicated) and often the file cannot be correctly class-dump'ed (as some data are actually outside of that library).

dyld_decache is a complete rewrite of the tool to solve the above problems. It correctly excludes irrelevant parts of the __LINKEDIT segments, and pulls in sections which are placed outside of the file due to dyld's optimization. As a result, the generated files take only roughly 200 MiB totally in size instead of over 4 GiB previously, and they can be correctly analyzed by class-dump.

The 64-bit dyld_decache for Mac OS X 10.6 can be downloaded from https://github.com/kennytm/Miscellaneous/downloads. It is a command line tool, the options are:

Usage:
  dyld_decache [-p] [-o folder] [-f name [-f name] ...] path/to/dyld_shared_cache_armvX

Options:
  -o folder : Extract files into 'folder'. Default to './libraries'
  -p        : Print the content of the cache file and exit.
  -f name   : Only extract the file with filename 'name', e.g. '-f UIKit' or
              '-f liblockdown'. This option may be specified multiple times to
              extract more than one file. If not specified, all files will be
              extracted.

machoizer.py

This is a small Python script that adds the necessary headers to turn a raw binary file (e.g. the decrypted iBoot) into a Mach-O file. This is useful for tools that cannot work with raw binary files, like otool -tv or the IDA Pro demo.

dump_stuff.py

This script is a collection of utilities to dump information from different libraries. Currently it supports dumping of CAAtom and UISound.

CAAtom is an internal data type in Core Animation which creates a mapping between strings and an integer index. This optimizes string comparison operation over known strings since they are already perfectly hashed. However, this poses a difficulty in reverse-engineering because the relevant strings are all replaced with some unrelated numbers. This script supports reading the table that defines the mappings of the internal atoms.

UISound is a directory in iOS containing .caf files for system alert sounds. These sounds are indiced by a constant number and can be used as the SoundID in AudioServices to play them. This script supports interpreting the sound IDs and categories for these files.

log_rename.idc

Often executables or kernels are stripped, so guessing what a function does would require heavy analysis of its content. Nevertheless, developers usually will leave a logging function which accepts __FUNCTION__, i.e. the function name, as an input parameter. If such a function is found, the function names can be assigned systematically.

The log_rename.idc script is written to take advantage of this. Once you have identified any function that takes a C string function name as an input parameter (via register r0 to r3), you could start this script to locate all analyzed functions calling this. Then the script will coservatively try to rename the function based on the input.

ipsw_decrypt.py

This is a convenient script to extract, decrypt and decompress files in an IPSW file in one pass. This script is only intended for decoding those files for analysis, but not for building a jailbroken IPSW. The standard jailbreaking software like PwnageTool or XPwn should be used instead for the latter purpose.

The script can perform the following:

  • Extract the encrypted files from an IPSW
  • Download decryption keys from http://theiphonewiki.com/
  • Perform AES decryption / VFDecrypt using these keys
  • Decompress the kernel into a Mach-O file, and iBootIm images into raw data.

This script requires the executables openssl (for AES decryption) and vfdecrypt (for decrypting the OS DMG) to run. It also requires the lxml module to be installed for HTML parsing.