PAC-RET Protection for Linux/AArch64 in Java

Pointer Authentication Codes (PAC) and Return Address Signing (RET) are security features available on certain ARM-based architectures, including AArch64. These features provide protection against control-flow attacks by ensuring the integrity of function return addresses. In this article, we will explore the concept of PAC-RET protection in Java on Linux/AArch64, along with proper examples and approaches.

Concept Explanation

PAC-RET protection involves signing function return addresses with a cryptographic key to detect and prevent control-flow attacks, such as return-oriented programming (ROP). It ensures that the return address is not tampered with by validating its authenticity during a function return. This protection is particularly relevant in mitigating code injection and control-flow hijacking attacks.

Approach and Examples

To demonstrate PAC-RET protection in Java on Linux/AArch64, we need to perform the following steps:

Step 1: Enable PAC-RET Support

To enable PAC-RET support, ensure that your Linux distribution is running on an AArch64 processor with the necessary hardware capabilities. Consult your system documentation or contact your platform provider for information on enabling PAC-RET.

Step 2: Enable PAC-RET in Java

Java 9 onwards provides support for PAC-RET through the JVM’s -XX:+PACRet option. This enables the PAC-RET instruction sequences during JIT (Just-In-Time) compilation.

Example Code:

Java

import com.sun.jna.Native;
import com.sun.jna.ptr.IntByReference;

public class PacRetExample {

    // Load the LibPAC library
    static {
        Native.register("pac");
    }

    // Function with PAC-RET protection
    public static int protectedFunction() {
        // Function logic goes here

        // Get the current return address
        long returnAddress = getCurrentReturnAddress();

        // Sign the return address
        long signedReturnAddress = signReturnAddress(returnAddress);

        // Store the signed return address for later verification

        // Return the protected value
        return 42;
    }

    // Helper method to retrieve the current return address
    private static long getCurrentReturnAddress() {
        // Use architecture-specific code to
          // retrieve the return address
        // Return the current return address
        return getCurrentReturnAddressNative();
    }

    // Helper method to sign the return address using LibPAC
    private static long signReturnAddress(long returnAddress) {
        IntByReference signature = new IntByReference();

        // Sign the return address using the LibPAC library
        signReturnAddressNative(returnAddress, signature);

        // Return the signed return address
        return signature.getValue();
    }

    // Native method declarations using JNA
    private static native long getCurrentReturnAddressNative();
    private static native void signReturnAddressNative(long returnAddress, IntByReference signature);

    public static void main(String[] args) {
        // Call the protected function
        int result = protectedFunction();

        // Process the protected result
        System.out.println("Protected function result: " + result);
    }
}

Code Explanation:

1. We import the necessary libraries, including com.sun.jna.Native for JNA (Java Native Access) functionality.
2. We define a static block to load the LibPAC library using Native.register.
3. The protectedFunction method represents a function with PAC-RET protection. It retrieves the current return address, signs it using signReturnAddress, stores the signed return address, and returns a protected value.
4. The getCurrentReturnAddress method retrieves the current return address using architecture-specific code (native method).
5. The signReturnAddress method signs the return address using the LibPAC library. It calls the signReturnAddressNative native method, passing the return address and an IntByReference object to receive the signature.
6. Native method declarations are provided using JNA annotations.
7. In the main method, we call the protectedFunction to demonstrate PAC-RET protection and print the result.

Conclusion

PAC-RET protection is a powerful technique to safeguard against ROP attacks by signing return addresses. By utilizing the LibPAC library and incorporating PAC-RET protection in Java code for Linux/AArch64, we can enhance the security of our applications. Remember to adapt and customize the code according to your specific requirements and ensure proper error handling and security practices.