EvanMcBroom

Switch Statements with Full Strings

C++11 introduced the constexpr keyword for defining a constant expression. A constant expression is a variable or function that may be evaluated at compile time. This has many uses, including extending a switch statement to support full strings.

Constant Expression Hash Functions

C++ only supports using an integer as the condition in a switch statement and an integer that is known at compile time in a case statement. You can define a hash function and use it to convert a string to an integer to use in a switch statement. If you define that hash function as a constexpr you can use it to convert a string literal to an integer to use in a case statement as well.

EvanMcBroom

// Copyright (C) 2022 Evan McBroom
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in

EvanMcBroom

Encrypting Strings at Compile Time

Thank you to SpecterOps for supporting this research and to Duane and Matt for proofreading and editing! Crossposted on the SpecterOps Blog.

TLDR: You may use this header file for reliable compile time string encryption without needing any additional dependencies.

Programmers of DRM software, security products, or other sensitive code bases are commonly required to minimize the amount of human readable strings in binary output files. The goal of the minimization is to hinder others from reverse engineering their proprietary technology.

Common approaches that are taken to meet this requirement often add an additional maintenance burden to the developer and are prone to error. These approaches will be presented along with t

EvanMcBroom

// Copyright (C) 2024 Evan McBroom

#include <Windows.h>
#include <iostream>
#include <vector>
#include <WbemCli.h>
#include <atlbase.h>
#include <iomanip>

// The modified, compiled IDL file from:

EvanMcBroom

IllBeBack - An Undocumented Function

Microsoft purchased the software Softricity SoftGrid in 2006 and renamed it to Microsoft Application Virtualization, or App-V for short. Windows shipped with several libraries in System32 and SysWOW64 to support App-V.

AppVTerminator.dll

One App-V library stands out from all the rest because it only has one exported function named IllBeBack... That's right! A library signed by Microsoft, with Terminator in the name, that only has a single callable function named IllBeBack.

EvanMcBroom

PIC and String Literals Part 2

I previously wrote about how to use macro metaprogramming to simplify using string literals in position independent code (PIC). The results are summarized in the below code snippet and the article can be read on GitHub.

void f() {
    // Example 1: The Pic idiom for instantiating a string
    char picString1[]{ 'a', 'b', 'c' };

EvanMcBroom

// Copyright (C) 2023 Evan McBroom
// Originally authored October 19th, 2023.
//
// Geoff Chappell first documented the format of the loader lock cookie on November 26th, 2008.
// His work is applied here to unlock the loader lock without knowing the original cookie that
// LdrLockLoaderLock returned. This same example code may be safely used in DllMain to unlock
// the loader lock and execute code that would otherwise deadlock the loader.
// Sources:
// - https://www.geoffchappell.com/studies/windows/win32/ntdll/api/ldrapi/lockloaderlock.htm
// - https://www.geoffchappell.com/studies/windows/win32/ntdll/api/ldrapi/unlockloaderlock.htm

EvanMcBroom

Perfect Loader Implementations

Thank you to SpecterOps for supporting this research and to Lee and Sarah for proofreading and editing! Crossposted on the SpecterOps Blog.

TLDR: You may use fuse-loader or perfect-loader as examples for extending an OS's native loader to support in-memory libraries.

Some software applications require the ability to load dynamic libraries from the memory of the application's own process. The majority of desktop OSes do not support this use case, so a number of developers have reimplemented the process of loading a library to overcome this limitation.

EvanMcBroom

Position Independent Code and String Literals

A common programming idiom when writing position independent code (PIC) is to expand a string literal into its individual characters when instantiating a local variable.

void f() {
    // Example 1: A normal instantiation with a string literal
    char a[]{ "a long string" };

 // Example 2: The Pic idiom for instantiating a string

EvanMcBroom

# Copyright (C) 2023 Evan McBroom

cmake_minimum_required(VERSION 3.21.0)
project(transacted-fmapi
    LANGUAGES CXX
)
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED YES)
set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>")