README.md

jnitrace-engine

Engine used by jnitrace to intercept JNI API calls.

jnitrace-engine is the project used by jnitrace to intercept and trace JNI API calls. It has been exposed as a separate project to allow Frida module developers to use the same engine to intercept and modify JNI API calls made by Android applications.

Installation:

The easiest way to get running with jnitrace-engine is using npm:

npm install jnitrace-engine

Simple Usage:

jnitrace-engine tries to mirror as much of the Frida API as possible. JNIInterceptor provides an API to attach to JNI API calls in a very similar way to the Frida Interceptor. The idea is to make using the library simple to use for those already familiar with Frida. The examples below are JavaScript but the module also supports TypeScript.

import { JNIInterceptor } from "jnitrace-engine";

// Attach to the JNI FindClass method
JNIInterceptor.attach("FindClass", {
    onEnter(args) {
        // called whenever the FindClass is about to be called
        console.log("FindClass method called");
        this.className = Memory.readCString(args[1]);
    },
    onLeave(retval) {
        // called whenever the FindClass method has finished executing
        console.log("\tLoading Class:", this.className);
        console.log("\tClass ID:", retval.get());
    }
});

Advanced Usage:

import { JNIInterceptor } from "jnitrace-engine";
import { JNILibraryWatcher } from "jnitrace-engine";
import { JNINativeReturnValue } from "jnitrace-engine";
import { ConfigBuilder } from "jnitrace-engine";

// configure the jnitrace-engine to limit what libraries to traces
const builder : ConfigBuilder = new ConfigBuilder();

builder.libraries = [ "libnative-lib.so" ]; // set a list of libraries to track
builder.backtrace = "fuzzy"; // choose the backtracer type to use [accurate/fuzzy/none]
builder.includeExports = [ "Java_com_nativetest_MainActivity_stringFromJNI" ]; // provide a list of library exports to track
builder.excludeExports = []; // provide a list of library exports to ignore
builder.env = true; // set whether to trace the JNIEnv struct or ignore all of it
builder.vm = false; // set whether to trace the JavaVM struct or ignore all of it

const config = builder.build(); //initialise the config - this makes it available to the engine

// An additional callback that can be used for listening to new libraries being loaded by an application
// Note this callback will be called for all libraries, not just the ones in the config
// libraries list
JNILibraryWatcher.setCallback({
    onLoaded(path : string) {
        console.log("Library Loaded " + path);
        console.log("Currently Traced Libraries", JSON.stringify(config.libraries));
    }
});

const findClassIntercept = JNIInterceptor.attach("FindClass", {
    onEnter(args: NativeArgumentValue[]) {
        console.log("Find Class called");
        args[1] = NULL; // Change the arguments to the FindClass function
        console.log("ThreadId", this.threadId);
        console.log("Address of FindClass method", this.jniAddress);
        this.backtrace.forEach((element: NativePointer) => {
            console.log("backtrace", element);
        });
    },
    onLeave(retval: JNINativeReturnValue) {
        // Change the retval to be returned to the caller of FindClass
        retval.replace(NULL);
        // Detach all JNI intercepts
        JNIInterceptor.detatchAll();
    }
});

JNIInterceptor.attach("CallDoubleMethodV", {
    onLeave(retval : JNINativeReturnValue) {
        // Log the method params of the Java method the JNI API is calling.
        // this.javaMethod will only exist if a Java method has been called.
        console.log("Java Method Args", JSON.stringify(this.javaMethod.params));
        // Detach from the FindClass intercept
        findClassIntercept.detach();
    }
});