jmp api+5 *2


Author: David Zimmer
Date: 09.09.12 - 8:26pm



I have been working to make an x64 build of sclog, which means redoing the hooking engine i built for it. I think I am going to go with the distorm/ntcoreHookingEngine. While I am playing with it, I am also adding several choices of hooks to embed. One in particular i wanted to see if I could add was a jmp api+5 safe hook that would allow the functions to still run.

After some experimentation i finally came up with a clean solution to this.

Its a 10 byte Api hook that looks like the following:
WinExec+0 e9 xxxxxxxx jmp My_HookProc
WinExec+5 e8 xxxxxxxx call UnwindProlog

#ifdef _M_IX86

void __stdcall output(ULONG_PTR ra){
	HOOK_INFO *hi = GetHookInfoFromFunction(ra);
	if(hi){
		printf("jmp+5 api caught %s\n", hi->ApiName );
	}else{
		printf("jmp+5 api caught %x\n", ra );
	}
}

void __declspec(naked) UnwindProlog(void){
	_asm{
		mov eax, [ebp-4] //return address
		sub eax, 10      //function entry point
		push eax         //arg to output
		call output

		pop eax      //we got here through a call from our api hook stub so this is ret
		sub eax, 10  //back to api start address
		mov esp, ebp //now unwind the prolog the shellcode did on its own..
		pop ebp      //saved ebp 
		jmp eax      //and jmp back to the api public entry point to hit main hook jmp
	}
}

#endif

So, if the api is called normally, the jmp hook works normally. If the shellcode does its own prolog and tries to get cute and do a jmp+5, the call hook comes into play. The reason i choose a call hook for the second transfer of execution is so that the return address is automatically saved. Since my hook is 10 bytes, we can calculate the function start address, and then look it up to see which api it was to display to the user. Once we do a user notification, and unwind the stack mods, we then transfer execution back to the apis start address, and let the jmp hook do its job as normal.

Simple, yet complicated all at once!

On another note...not all API can support a 10 byte hook, For simplicity I think I will make it do an automatic fall back to a standard jmp hook if there isnt enough room. Also for x64 Win7 hooks, I will have to do conditional compilations for certain api like GetProcAddress, which just forward to exports of kernelbase.dll now.




Comments: (0)

 
Leave Comment:
Name:
Email: (not shown)
Message: (Required)
Math Question: 90 + 13 = ? followed by the letter: L 



Twitter
RSS
About Me
More Blogs
Main Site
Posts: (year)
2021 (1)
     VB App object
2020 (8)
     AutoIT versions
     IDA JScript 2
     Using VB6 Obj files from C
     Vb6 PCode Internals
     Vb6 Runtime ForLoop Disasm
     VB6 Pcode - For Loops
     Yara Corrupt Imports
     Yara Undefined values
2019 (12)
     Yara WorkBench
     SafeArrayGetVartype
     vbdec dbg updates
     vb6 PCode NOP
     vb6 API and call backs
     how pcode works Pt1
     PrintFile
     ImpAdCallNonVirt
     Reversing PCode Args
     VB6 PCode Disassembly
     VB6 PCode Debugger
     UConnect Disable Cell Modem
2017 (5)
     IDA python over IPC
     dns wildcard blocking
     64bit IDA Plugins
     anterior lines
     misc news/updates
2016 (4)
     KANAL Mod
     Decoders again
     CDO.Message Breakpoints
     SysAnalyzer Updates
2015 (6)
     SysAnalyzer and Site Updates
     crazy decoder
     ida js w/dbg
     flash patching #2
     JS Graphing
     packet reassembly
2014 (5)
     Delphi IDA Plugin
     scdbg IDA integration
     API Hash Database
     Winmerge plugin
     IDACompare Updates
2013 (9)
     Guest Post @ hexblog
     TCP Stream Reassembly
     SysAnalyzer Updates
     Apilogger Video
     Shellcode2Exe trainer
     scdbg updates
     IDA Javascript w/IDE
     Rop Analysis II
     scdbg vrs ROP
2012 (13)
     flash patching
     x64 Hooks
     micro hook
     jmp api+5 *2
     SysAnalyzer Updates
     InjDll runtime config
     C# Asm/Dsm Library
     Shellcode Hook Detection
     Updates II
     findDll
     Java Hacking
     Windows 8
     Win7 x64
2011 (19)
     Graphing ideas
     .Net Hacking
     Old iDefense Releases
     BootLoaders
     hll shellcode
     ActionScript Tips
     -patch fu
     scdbg ordinal lookup
     scdbg -api mode
     Peb Module Lists
     scdbg vrs Process Injection
     GetProcAddress Scanner
     scdbg fopen mode
     scdbg findsc mode
     scdbg MemMonitor
     demo shellcodes
     scdbg download
     api hashs redux
     Api hash gen
2010 (11)
     Retro XSS Chat Codes
     Exe as DLL
     Olly Plugins
     Debugging Explorer
     Attach to hidden process
     JS Refactoring
     Asm and Shellcode in CSharp
     Fancy Return Address
     PDF Stream Dumper
     Malcode Call API by Hash
     WinDbg Cheat Sheet
2009 (1)
     GPG Automation