Theodosius - Jit linker, Mapper, Mutator, and Obfuscator

Theodosius (Theo for short) is a jit linker created entirely for obfuscation and mutation of both code, and code flow. The project is extremely modular in design and supports both kernel and usermode projects. Since Theo inherits HMDM (highly modular driver mapper), any vulnerable driver that exposes arbitrary MSR writes, or physical memory read/write can be used with this framework to map unsigned code into the kernel. This is possible since HMDM inherits VDM (vulnerable driver manipulation), and MSREXEC (elevation of arbitrary MSR writes to kernel execution).

Theo can be used for many projects. The modularity of the code allows for a programmer to use this framework however they please. A few example usages of Theo would be, streaming code and data from a .lib over a network directly into memory, resolving unexported symbols via PDB, allocating each instruction of a function inside of code caves, and much more.

Table Of Contents

• Theodosius - Jit linker, Mapper, Mutator, and Obfuscator
  • Credit And Dependencies
  • Linking - Dynamic And Static
    • What Is A Linker
    • Object Files
    • Static Linking
    • Dynamic Linking
  • Usage - Using Theodosius
    • Integrating Clang
      • Requirements
• RIP Relative Addressing
• License - BSD 3-Clause

Credit And Dependencies

• BTBD - Huge thanks for providing suggestions and bouncing ideas back and forth.
  • SMAP - scatter mapper, this project is heavily influenced by SMAP.
• Zydis - used to decompile obfuscated routines and find JCC's.
• asmjit - used to generate link-time code (mutated routines).
• LLVM-Obfuscator - Here are the following devs:
  • Pascal Junod
  • Julien Rinaldini
  • Johan Wehrli
  • Julie Michielin
  • Stéphane Ongagna
  • Grégory Ruch
  • Sébastien Bischof

Linking - Dynamic And Static

What Is A Linker

A linker is a program which takes object files produces by a compiler and generates a final executable native to the operating system. A linker interfaces with not only object files but also static libraries, "lib" files. What is a "lib" file? Well a lib file is just an archive of obj's. You can invision it as a zip/rar without any compression, just concatination of said object files.

Theo is a jit linker, which means it will link objs together and map them into memory all at once. For usability however, instead of handling object files, Theo can parse entire lib files and extract the objects out of the lib.

Object Files

If you define a c++ file called "main.cpp" the compiler will generate an object file by the name of "main.obj". When you refer to data or code defined in another c/c++ file, the linker uses a symbol table to resolve the address of said code/data. In this situation I am the linker and I resolve all of your symbols :).

Static Linking

Static linking is when the linker links entire routines not created by you, into your code. Say memcpy (if its not inlined), will be staticlly linked with the CRT. Static linking also allows for your code to be more independant as all the code you need you bring with you. However, with Theo, you cannot link static libraries which are not compiled with mcmodel=large. Theo supports actual static linking, in other words, using multiple static libraries at the same time.

Dynamic Linking

Dynamic linking is when external symbols are resolved at runtime. This is done by imports and exports in DLL's (dynamiclly linked libraries). Theo supports "dynamic linking", or in better terms, linking against exported routines. You can see examples of this inside of both usermode and kernelmode examples.

Usage - Using Theodosius

Integrating Clang

For integration with visual studios please open install llvm2019 extension, or llvm2017 extension. Once installed, create or open a visual studio project which you want to use with LLVM-Obfuscator and Theo. Open Properties --> Configuration Properties ---> General, then set Platform Toolset to LLVM.

Once LLVM is selected, under the LLVM tab change the clang-cl location to the place where you extracted clang-cl.rar. Finally under Additional Compiler Options (same LLVM tab), set the following: -Xclang -std=c++1z -Xclang -mcode-model -Xclang large -Xclang -fno-jump-tables -mllvm -split -mllvm -split_num=4 -mllvm -sub_loop=4.

Please refer to the LLVM-Obfuscator Wiki for more information on commandline arguments.

Requirements

• No SEH support, do not add __try/__except in your code.
• No CFG (control flow guard) support. Please disable this in C/C++ ---> Code Generation ---> Control Flow Guard
• No Stack Security Check Support. Please disablel this in C/C++ ---> Code Generation ---> Security Check (/GS-)
• Your project must be set to produce a .lib file.
• Your project must not link with other static libraries which are not compiled with -Xclang -mcmodel-large.
• Project must be compiled with the following flags
  • -Xclang -mcmodel=large, removes RIP relative addressing besides JCC's.
  • -Xclang -fno-jump-tables, removes jump tables created by switch cases.
  • /Zc:threadSafeInit-, static will not use TLS (thread local storage).

RIP Relative Addressing

In order to allow for a routine to be scattered throughout a 64bit address space, RIP relative addressing must not be used. In order to facilitate this, a very special version of clang-cl is used which can use mcmodel=large. This will generate instructions which do not use RIP relative addressing when referencing symbols outside of the routine in which the instruction itself resides. The only exception to this is JCC instructions, (besides call) also known as branching instructions. Take this c++ code for an example:

ObfuscateRoutine 
extern "C" int ModuleEntry()
{
	MessageBoxA(0, "Demo", "Hello From Obfuscated Routine!", 0);
	UsermodeMutateDemo();
	UsermodeNoObfuscation();
}

This c++ function, compiled by clang-cl with mcmodel=large, will generate a routine with the following instructions:

0x00:                               ; void UsermodeNoObfuscation(void)
0x00:                                               public ?UsermodeNoObfuscation@@YAXXZ
0x00:                               ?UsermodeNoObfuscation@@YAXXZ proc near ; CODE XREF: ModuleEntry+42↓p
0x00:                               var_4           = dword ptr -4
0x00: 48 83 EC 28                                   sub     rsp, 28h
0x04: C7 44 24 24 00 00 00 00                       mov     [rsp+28h+var_4], 0
0x0C:                               loc_C:
0x0C: 83 7C 24 24 05                                cmp     [rsp+28h+var_4], 5
0x11: 0F 83 38 00 00 00                             jnb     loc_4F
0x17: 31 C0                                         xor     eax, eax
0x19: 48 BA 28 01 00 00 00 00 00 00                 mov     rdx, offset ??_C@_04DKDMNOEB@Demo?$AA@ ; "Demo"
0x23: 49 B8 00 01 00 00 00 00 00 00                 mov     r8, offset ??_C@_0CD@JEJKPGNA@Hello?5... ; "Hello From Non-Obfuscated Routine!"
0x2D: 48 B8 A0 01 00 00 00 00 00 00                 mov     rax, offset MessageBoxA
0x37: 45 31 C9                                      xor     r9d, r9d        ; uType
0x3A: 44 89 C9                                      mov     ecx, r9d        ; hWnd
0x3D: FF D0                                         call    rax ; MessageBoxA
0x3F: 8B 44 24 24                                   mov     eax, [rsp+28h+var_4]
0x43: 83 C0 01                                      add     eax, 1
0x46: 89 44 24 24                                   mov     [rsp+28h+var_4], eax
0x4A: E9 BD FF FF FF                                jmp     loc_C
0x4F:                               loc_4F:
0x4F: 48 83 C4 28                                   add     rsp, 28h
0x53: C3                                            retn
0x53:                               ?UsermodeNoObfuscation@@YAXXZ endp

As you can see from the code above, (sorry for the terrible syntax highlighting), references to strings and calls to functions are done by first loading the address of the symbol into a register and then interfacing with the symbol.

0x2D: 48 B8 A0 01 00 00 00 00 00 00                 mov     rax, offset MessageBoxA
; ...
0x3D: FF D0                                         call    rax ; MessageBoxA

Each of these instructions can be anywhere in virtual memory and it would not effect code execution one bit.

License - BSD 3-Clause

Copyright (c) 2021, _xeroxz All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

• Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.