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APK Instrumentation

Warning: This is a repository with quick-and-dirty code rewriting tools based on Soot which I use for my own research. It has only been tested with Soot 4.2.1. The documentation is limited and support cannot be provided. Use at your own risk!

Getting started

You can download apk-instrumentation.jar from the Releases section of this repository. It is self-contained and requires nothing but Java. If you want to build it yourself, you will need Python 3 and Soot (JAR file with all dependencies). You then run the build command:

./build /path/to/soot-jar-with-dependencies.jar

To start the APK conversion process, use the following command:

java -jar apk-instrumentation.jar [--config /path/to/config.properties] [action]

action can be either rewrite (default) or decompile. It is recommendable to run decompile action (produces Jimple code) before configuring rewriting steps, output of other decompilers might be incompatible e.g. when determining call signatures.

If no path to config.properties is given on the command line, the file is assumed to be present in the current directory. Its entries determine what code transformations should be performed.

General configuration options

The following configuration options are independent of the components enabled:

  • sdk: (optional) directory where the Android SDK is installed. If omitted, ANDROID_HOME environment variable has to be set.
  • platformVersion: (optional) platform version to be loaded in Android SDK. If omitted, will be detected automatically.
  • input: path to the input APK file
  • output: path of the rewritten APK file to be written
  • decompileDir: path to write decompiled Jimple code to
  • keystore: (optional) path to the key store containing the signing key
  • keypass: (optional) password protecting the key store

Method filters

Some configuration options use method filters determining which methods are included. These are space-separated lists, entries can have the following format:

  • com.example.test.*: includes all classes with names matching a particular prefix
  • com.example.test.Main:*: includes all methods of a specific class
  • com.example.test.Main:dump(java.lang.String,int): includes only the method with the specified signature

Extended format strings

Some components will allow specifying extended format strings for data to be logged. These use the usual Java format specifiers like %s or %i but require specifying the input as well, e.g. {this:%s} (format this value as a string) or {arg2:%i} (format second parameter as integer). The following input specifiers are possible:

  • method: The signature of the calling method
  • result: Call result if available
  • this: Instance reference
  • argNN: Argument value where NN is the argument’s zero-based position
  • args: Comma-separated list of all arguments (stringified)

In addition, the format specifier %x is treated specially: System.identityHashCode() will be called on the corresponding input and the result hex-formatted.

ClassReplacer component

This component will load classes from .jimple files and replace existing files with them. You can take the .jimple file for a class from the decompilation output, modify it as needed and give the result to this component to replace the original with it.

Note: This will do nothing for classes that don’t exist in the original archive.

Configuration options:

  • ClassReplacer.enabled: add to enable this component
  • ClassReplacer.classes: list of paths to .jimple files

CallLogger component

This component will add logging code after calls to specified methods. See config.properties.downloads for a configuration example logging URLConnection interactions.

Configuration options:

  • CallLogger.enabled: add to enable this component
  • CallLogger.filter: (optional) restricts functionality to a set of methods, for value format see Method filters section above
  • CallLogger.tag: (optional) log tag to be used (default is CallLogger)
  • CallLogger.<method filter>: specifies that calls to the specified method should be logged. <method filter> is a method specification as outlined in the Method filters section above. Note that .properties format requires colons to be prefixed with a backslash: \:. The value is a format string (see Extended format strings section above).

StreamLogger component

This component will wrap InputStream and OutputStream instances returned by specified methods to log data being sent or received. See config.properties.downloads for a configuration example logging streams returned by URLConnection.getInputStream() and URLConnection.getOutputStream().

Configuration options:

  • StreamLogger.enabled: add to enable this component
  • StreamLogger.filter: (optional) restricts functionality to a set of methods, for value format see Method filters section above
  • StreamLogger.tag: (optional) log tag to be used (default is StreamLogger)
  • StreamLogger.<method filter>: specifies a call returning a stream that should be wrapped. <method filter> is a method specification as outlined in the Method filters section above. Note that .properties format requires colons to be prefixed with a backslash: \:. The value is a format string that will be used as a prefix for logged data (see Extended format strings section above).

MethodLogger component

This component will add logging to the start of a method. This might be more efficient than CallLogger for methods called from many places, and it will log even calls resulting in an exception. The disadvantage is that the method’s return value cannot be logged as it isn’t known at this stage.

Configuration options:

  • MethodLogger.enabled: add to enable this component
  • MethodLogger.tag: (optional) log tag to be used (default is MethodLogger)
  • MethodLogger.<method filter>: specifies a method that should be logged. <method filter> is a method specification as outlined in the Method filters section above. Note that .properties format requires colons to be prefixed with a backslash: \:. The value is a format string like Entered method {method:%s} ({args:%s}) (see Extended format strings section above).

AssignmentRemover component

This component will remove any assignments with the specified result type. Note that Jimple does not support nested expressions, so any intermediate result is assigned to a local variable.

Configuration options:

  • AssignmentRemover.enabled: add to enable this component
  • AssignmentRemover.filter: (optional) restricts functionality to a set of methods, for value format see Method filters section above
  • AssignmentRemover.type: the result type identifying the assignment to be removed

CallRemover component

This component will remove any calls to the specified method(s).

Configuration options:

  • CallRemover.enabled: add to enable this component
  • CallRemover.filter: (optional) restricts functionality to a set of methods, for value format see Method filters section above
  • CallRemover.method: specifies the method(s) to be removed, for value format see Method filters section above