Intercept arbitrary functions at run-time, without knowing their typedefs
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Latest commit 0d542ff Apr 13, 2017

README.md

UniHook

Pre-Alpha Source Code, seriously there are issues!! THIS IS A POC. This is an example project on how to use PolyHook to intercept ANY arbitrary function, without knowing it's typedef. It hooks the specified function and calls an "Interupt" function before and after executing the original hooked function. This is useful for cases where someone may wish to time how long a function takes to execute. This relies both on PolyHook,and it's dependancy Capstone (the modified branch in my GitHub).

How it works:

It allocates a callback at runtime that PolyHook redirects the hooked function to. This callback is filled with assembly at runtime that will handle executing the intercepts, and the original function. This is done by first storing all registers, calling the intercept, and restoring the registers, then it calls the original function, and repeats the register storing and poping before it calls the second interupt and returns to the caller of the hooked function.

Caller->Store Regs->Interupt1->Restore Regs->Original Hooked Func->Store Regs->Interupt2->Restore Regs->Return to Caller

Project Setup

This demo has 3 core parts

  1. PolyHook for hooking backend
  • PolyHook relies on Capstone for disassembly
  1. UniHook dll which uses polyhook, and then creates runtime callbacks
  2. UniHook loader which injects the UniHook dll, and sends it commands via a shared memory queue/stack system
  • Shared memory synchronization is done through the Shared Memory Mutex object, which uses a WINAPI named mutex, this object can be managed by c++11's locking wrappers such as lock_guard

LIMITATIONS

  1. No XMM registers or SIMD instructions can be used when compiling in x64, my variation of pusha and popa doesn't restore these.
  2. Possible stack alignment issues may exist when the original function is executed after the first interupt
  3. A heap corruption bug is floating around somewhere

LICENSE

MIT