zpoline - High-Performance Linux System Call Hook Neglecting Kernel Changes

Introducing zpoline: A Revolutionary System Call Hook for Linux

zpoline is a cutting-edge system call hook mechanism designed specifically for Linux environments. With its unique attributes, zpoline stands out as a state-of-the-art solution for developers who require efficient system call hooking in their applications.

Key Advantages of zpoline

Speed: zpoline operates 100 times faster than the traditional ptrace method, making it an incredibly fast solution for system call hooking. This can significantly improve performance for applications that rely heavily on system calls.
Complete Coverage: Unlike many other solutions, zpoline provides 100% coverage, allowing it to exhaustively hook all system calls. This means developers can be confident that no system call goes untracked.
No Source Code Needed: Developers can implement zpoline without access to the source code of user-space programs. This makes it an excellent choice when integrating with third-party applications or legacy systems where source code is unavailable.
No Kernel Modifications: Implementing zpoline does not require changes to the operating system kernel, nor does it necessitate the installation of additional kernel modules. This means a simpler, faster setup and fewer concerns about compatibility issues with future kernel updates.

zpoline is an excellent fit for those situations where ptrace is too slow, when LD_PRELOAD tricks fall short due to their inability to cover all system calls, when source code is unavailable, or when one prefers avoiding kernel modifications or use of additional modules.

The zpoline Technique

zpoline falls under the category of binary rewriting. Unlike traditional methods that risk overwriting program binaries, zpoline safely manipulates code in memory, ensuring the integrity of your program binaries. The setup process involves rewriting code loaded into memory just before the main function of a user-space program executes.

The standout feature of zpoline is its ability to reliably hook system calls—something that has historically been challenging for binary rewriting approaches.

The innovative approach involves leveraging the calling convention and creating a special trampoline code. Essentially, zpoline replaces the syscall and sysenter instructions with callq *%rax. A crafted trampoline code is introduced at the virtual address 0, thus inspiring the name "zpoline"—a fusion of zero ("z") and trampoline.

Implementation Details

Platform Compatibility: Currently, zpoline is built for Linux operating systems running on x86-64 architecture.

Dependencies: It utilizes the disassembler in libopcodes, part of binutils, which can be installed using the following command:

sudo apt install binutils-dev

Core Library Files:

apps/basic/libzphook_basic.so: Implements the hook function.
libzpoline.so: Loaded using LD_PRELOAD, configures the trampoline code, performs binary rewriting, and dynamically loads the hook function library using dlmopen.

Building and Setup

To compile the necessary files, use the following commands:

make -C apps/basic
make

For zpoline to function, set the kernel parameter for minimum memory mapping address:

sudo sh -c "echo 0 > /proc/sys/vm/mmap_min_addr"

Please note SELinux might interfere by blocking mmap at address 0; temporarily disabling SELinux can resolve this, but it poses security risks and should be done cautiously.

Usage

To deploy zpoline, specify library paths using environment variables:

LIBZPHOOK=./apps/basic/libzphook_basic.so LD_PRELOAD=./libzpoline.so [program you wish to run]

In this configuration, libzpoline.so employs dlmopen to access the hook function library specified by LIBZPHOOK.

Custom Hook Function

Developers can create custom hook functions independent of libzpoline.so. By implementing __hook_init, developers can direct the hook function to their specified logic, thus extending zpoline’s capabilities to suit specific application needs.

Additional Resources

Research Paper: A detailed academic paper on zpoline was presented at USENIX ATC 2023, covering its technical foundations and comparisons with existing systems.
Supplemental Documentation: Additional guides and documentation can be found in the repository's Documentation/README.md.
Source Code Commentary: Since detailed developer comments are embedded within the source code, they serve as an invaluable resource for understanding the system's implementation intricacies.

zpoline represents an exciting advancement in system call hooking for Linux, combining speed, comprehensive coverage, and ease of integration without requiring kernel modifications. It is poised to offer developers a robust tool for enhancing their application's interaction with the operating system.