Keypatch

Keypatch is the award winning plugin of IDA Pro for Keystone Assembler Engine.

Keypatch consists of 3 tools inside.

• Patcher & Fill Range: these allow you to type in assembly to directly patch your binary.
• Search: this interactive tool let you search for assembly instructions in binary.

See this quick tutorial for how to use Keypatch, and this slides for how it is implemented.

Keypatch is confirmed to work on IDA Pro version 6.4, 6.5, 6.6, 6.8, 6.9, 6.95 but should work flawlessly on older versions. If you find any issues, please report.

---

1. Why Keypatch?

Sometimes we want to patch the binary while analyzing it in IDA, but unfortunately the built-in asssembler of IDA Pro is not adequate.

• This tool is not friendly and without many options that would make the life of reverser easier.
• Only X86 assembler is available. Support for all other architectures is totally missing.
• The X86 assembler is not in a good shape, either: it cannot understand many modern Intel instructions.

Keypatch was developed to solve this problem. Thanks to the power of Keystone, our plugin offers some nice features.

• Cross-architecture: support Arm, Arm64 (AArch64/Armv8), Hexagon, Mips, PowerPC, Sparc, SystemZ & X86 (include 16/32/64bit).
• Cross-platform: work everywhere that IDA works, which is on Windows, MacOS, Linux.
• Based on Python, so it is easy to install as no compilation is needed.
• User-friendly: automatically add comments to patched code, and allow reverting (undo) modification.
• Open source under GPL v2.

Keypatch can be the missing piece in your toolset of reverse engineering.

---

2. Install

• Install Keystone core & Python binding for Python 2.7 from keystone-engine.org/download. Or follow the steps in the appendix section.

• Copy file keypatch.py to IDA Plugin folder, then restart IDA Pro to use Keypatch.

  • On Windows, the folder is at C:\Program Files (x86)\IDA 6.9\plugins
  • On MacOS, the folder is at /Applications/IDA\ Pro\ 6.9/idaq.app/Contents/MacOS/plugins
  • On Linux, the folder may be at /opt/IDA/plugins/

NOTE

• On Windows, if you get an error message from IDA about "fail to load the dynamic library", then your machine may miss the VC++ runtime library. Fix that by downloading & installing it from https://www.microsoft.com/en-gb/download/details.aspx?id=40784
• On other *nix platforms, the above error message means you do not have 32-bit Keystone installed yet. See appendix section below for more instructions to fix this.

---

3. Usage

• For a quick tutorial, see TUTORIAL.md. For a complete description of all of the features of Keypatch, keep reading.

• To patch your binary, press hotkey CTRL+ALT+K inside IDA to open Keypatch Patcher dialog.

  • The original assembly, encode & instruction size will be displayed in 3 controls at the top part of the form.
  • Choose the syntax, type new assembly instruction in the Assembly box (you can use IDA symbols).
  • Keypatch would automatically update the encoding in the Encode box while you are typing, without waiting for ENTER keystroke.
    • Note that you can type IDA symbols, and the raw assembly will be displayed in the Fixup control.
  • Press ENTER or click Patch to overwrite the current instruction with the new code, then automatically advance to the the next instruction.
    • Note that when size of the new code is different from the original code, Keypatch can pad until the next instruction boundary with NOPs opcode, so the code flow is intact. Uncheck the choice NOPs padding until next instruction boundary if this is undesired.
    • By default, Keypatch appends the modified instruction with the information of the original code (before being patched). Uncheck the choice Save original instructions in IDA comment to disable this feature.
  • By default, the modification you made is only recorded in the IDA database. To apply these changes to the original binary (thus overwrite it), choose menu Edit | Patch program | Apply patches to input file.

• To fill a range of code with an instruction, select the range, then either press hotkey CTRL+ALT+K, or choose menu Edit | Keypatch | Fill Range.
  • In the Assembly box, you can either enter assembly code, or raw hexcode. Some examples of acceptable raw hexcode are 90, aa bb, 0xAA, 0xBB.

• To revert (undo) the last patching, choose menu Edit | Keypatch | Undo last patching.

• To search for assembly instructions (without overwritting binary), open Keypatch Search from menu Edit | Keypatch | Search.

  • Choose the architecture, address, endian mode & syntax, then type assembly instructions in the Assembly box.
  • Keypatch would automatically update the encoding in the Encode box while you are typing, without waiting for ENTER keystroke.
  • When you click Search button, Keypatch would look for all the occurences of the instructions, and show the result in a new form.

• To check for new version of Keypatch, choose menu Edit | Keypatch | Check for update.

• At any time, you can also access to all the above Keypatch functionalities just by right-click in IDA screen, and choose from the popup menu.

---

4. Contact

Email keystone.engine@gmail.com for any questions.

For future update of Keypatch, follow our Twitter @keystone_engine for announcement.

---

Appendix. Install Keystone for IDA Pro

IDA Pro's Python is 32-bit itself, so it can only loads 32-bit libraries. For this reason, we have to build & install Keystone 32-bit. This section details the steps towards that goal.

A1. Windows

It is easiest to just download & install Python 2.7 module for Windows from http://www.keystone-engine.org/download. Be sure to get the 32-bit version, regardless of your Windows edition.

If you prefer to compile from source, just use MSVC 32-bit & follow the instructions in Windows documentation to build keystone.dll. After that, install Python module as in Python documentation. Then copy keystone.dll to the directory of Keystone Python module.

A2. MacOS

Install the core & Python module of Keystone with the following command:

$ sudo pip install keystone-engine

In case IDA still complains "ImportError: No module named keystone" when Keypatch is loading, then do the following step to copy Keystone Python binding to IDA directory. (replace 6.8 with your actual IDA version)

$ sudo cp -r /Library/Python/2.7/site-packages/keystone /Applications/IDA\ Pro\ 6.8/idaq.app/Contents/MacOS/python

A3. Linux

First of all, be sure that your machine already have Cmake installed. On Ubuntu, you can install Cmake with:

$ sudo apt-get install cmake

Then if your system is Linux 32-bit, you can install Keystone via pip as with MacOS above.

$ sudo pip install keystone-engine

In case you are on 64-bit Linux, you need to cross compile Keystone to 32-bit. Since version 0.9.1, Keystone supports lib32 option to make this easy. After building the core, install Python module as in Python documentation.

Note that to cross-compile on Linux, you need to install some multilib libraries. For example, on Ubuntu 14.04 64-bit, do this with:

$ sudo apt-get install lib32stdc++-4.8-dev libc6-dev-i386

After having multilib dependencies, run the following commands in the source directory of Keystone.

$ mkdir build
$ cd build
$ ../make-share.sh lib32 lib_only

Then copy Python bindings to IDA's Python directory, together with disutils from your distro's Python to IDA's Python, like following. (Use your actual IDA directory instead)

$ sudo cp -r bindings/python/keystone /opt/IDAPro6.8/python/
$ sudo cp -r /usr/lib/python2.7/distutils /opt/IDAPro6.8/python/

Finally, copy the 32-bit libraries of Keystone to the Python directory of IDA Pro, like following.

$ sudo cp build/llvm/lib/libkeystone.so.* /opt/IDAPro6.8/python/keystone/

These complicated workarounds are necessary because IDA in Linux 64 bit doesn't use the system's Python.

Done? Now go back to section 2 & install Keypatch for IDA Pro. Enjoy!