About this video

• Video Title: PE File Structure, IDT, IAT, и Relocations. Самая важная тема в реверсе.
• Channel: Internals
• Speakers: None explicitly named, but likely a single speaker.
• Duration: 00:32:21

Overview

This video provides a detailed explanation of the Portable Executable (PE) file structure, focusing on its critical components like the Import Directory Table (IDT), Import Address Table (IAT), and Relocation Table. The speaker emphasizes the importance of understanding PE files for reverse engineering, malware analysis, and cybersecurity.

Key takeaways

• PE File Structure Importance: Understanding PE files is fundamental for reverse engineering, enabling tasks ranging from malware creation to its eradication, and aiding in the analysis of obfuscated and packed executables.
• DOS Header: This header is present for historical compatibility with MS-DOS, indicating whether a program is suitable for DOS execution.
• NT Headers: Crucial for identifying the PE file as valid and containing essential information for the Windows Loader. This includes the PE signature and the optional header.
• Optional Header: While named "optional," it is mandatory for executable files and contains vital information like the size of code, initialized data, entry point address, and base of code. It also specifies architecture details and memory alignment.
• Section Headers: Define the location, size, and characteristics of different sections within the PE file (e.g., .text for code, .data for initialized data, .rdata for read-only data).
• Data Directory Array: Points to various important data structures within the PE file, including the Import Directory Table (IDT) and the Import Address Table (IAT).
• Import Directory Table (IDT) and Import Address Table (IAT): The IDT lists the DLLs the executable depends on, while the IAT stores the addresses of the imported functions, which are resolved at runtime.
• Relocation Table: Crucial for dynamically loaded libraries (DLLs) and position-independent executables. It allows the loader to adjust addresses in the code if the executable is loaded at a different base address than initially intended, ensuring proper function.

The Relocation Table helps when a PE file is loaded at a different base address by allowing the loader to adjust addresses within the code. If the executable is loaded at an unexpected Image Base, the relocation table contains information indicating which addresses need to be modified. The system calculates a delta (new base minus old base) and adds this delta to the addresses listed in the relocation table to ensure they point to the correct locations in memory. This process corrects potentially invalid or non-functional addresses, resulting in a new, valid address.