ida_kcpp

An IDAPython module for way more convienent way to Reverse Engineering iOS kernelcaches.

Big part of the iOS kernelcache is written by C++, which compiled into complicated binary code use many virtual table derefences rather than explicit direct calls.ida_kcpp takes the advanteage of ida_kernelcache classes hierarchy reconstruction. It maps the IDB and synchronizes the binary functions and the original virtual methods. It enables navigation through the iOS kernelcache by double-clicking on c++ virtual methods call, finding their xrefs, and keeping all of it synchronized during live research.

ida_kcpp is inspired by ida_medigate but benefits from the unique structure of the iOS kernelcache and provides more powerful and convenient research environment.

Installation

1. Install ida_kernelcache(Cellebrite's fork)
2. Make sure ida_kernelcache and ida_kcpp are in IDA python path.

Could also be added by adding into ~/.idapro/idapythonrc.py:

import sys
sys.path.append(IDA_KCPP_PATH)
sys.path.append(IDA_KERNELCACHE_PATH)

2. clone the repository and symlink ~/.idapro/plugins/ida_kcpp_plugin.py to ida_kcpp_plugin.py
3. Install ida-netnode
4. [Optional]: Install ida-referee if decompiler structs fields xrefs tracking is required

Usage

Preliminary Analysis

1. Open analyzed kernelcache. If ida_kernelcache has not run yet, please run it edit >> Plugins >> Kernel Cache CPP >> ida_kernelcache process kernel
2. Run Edit >> Plugins >> Kernel Cache CPP >> Perform Initial sync... (Some warning messageboxes might appear, you can ignore them for now). This step renames Virtual functions names by setting their prefix to the class they belong. This step also decompiles all the virtual functions, sets their this argument, and changes the relevant ::vmethods member to be a function pointer to the decompiled type. This step can take a while...
3. Now there is a "Synced IDB", but pay attention - the plugin isn't activated yet.

Plugin activating for a synced IDB

ida_kcpp automatically propagates names and prototypes, and also changes some aspects of navigation in IDA, hence is not activated automatically but at any point may be activated or deactivated.

Activate ida_kcpp by clicking on edit >> Plugins >> Kernel Cache CPP >> Activate Plugin (This will install the Hexrays hooks and also run ida_kernelcache.collect_class_info())

Deactivate the plugin

clicking on Edit >> Plugins >> Kernel Cache CPP >> Deactivate Plugin

Features overview

Virtual functions synchronizer

Virtual function renaming

When renaming a virtual function one may edit the mangled name (for example __ZNK10AppleA7IOP9method_86Ev_99), or change it to human-being names (AppleA7IOP::method_86) which will be mangled automatic. The relevant ANCESTOR::vmethods member will be renamed as well, and also all of the virtual functions that implement the same virtual method will be renamed too.

Virutal function prototype updating

The same goes for virutal function prototype changing. In this case, the relevant ANCESTOR::vmethods member's prototype will be changed to a function pointer to the type that just was set, with setting this as ANCESTOR *. Also, the prototypes of all of the relevant virtual method implementations of the ANCESTOR's DESCENDANTS will be changed, with setting their this to DESCENTANT *.

Improved XREFS

• We add an xref from every virtual function to it's abstract ::vmethods member.
• Using ida_referee we can track uses of every field, and especially ::vmethods member (virtual calls) in the decompiler.
  • We also added CTRL+SHIFT+Y hotkey from virtual function, to directly opening the xrefs window to its relevant ::vmethod member. IDA has a bug and this only works from the disassembly window and not from the decompiler.

Improved Navigation

• Decompiler: Double click on a virtual function call pops up a window that allowing the user to choose the implementation of the virtual method.

  

• Structures window:

  • Double click on virtual method pops up the same window as in the decompiler
  • Fixed an IDA bug that double-click on struct name that contains :: won't jump.

Future improvements

1. Adding support in IDA7.2 c++ classes compatibility. Require changing ida_kernelcache structs layout which we didn't do yet for legacy reason
2. Adding a name/prototype resolving interface for conflicts.

Meta

Authored by Uriel Malin and Ievgen Solodovnykov of Cellebrite Labs. Developed and tested for IDA8.0 on macOS with python 3.10.2