pimzero / jinterpose

Like LD_PRELOAD but for Java

JInterpose

LD_PRELOAD, but for Java applications.

This is a proof-of-concept - there is a lot to do to be actually useful.

This leverages the Java Agent feature to instrument the application, and ASM to edit the code at runtime.

The configuration is in protobuf Text Format. The format is defined in com/pimzero/jinterpose/Proto.proto.

While the user needs to keep in mind low-level Java details in mind while writing the configuration, this project aims to describe the instrumentations/transformations in the configuration file in a "declarative" manner.

Dependencies:

• asm
• protobuf-java

The build system is GNU Makefile, as I am not used to standard Java ecosystem tools. This has the following drawbacks:

• Dependencies versions need to be updated manually in the Makefile
• Dependencies between files need to be explicitly defined manually

Example

The initial goal of this project was to have a "pretty" dark-mode in bindiff (although not needed anymore now that bindiff is opensource 😊). While the -Dswing.defaultlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel goes a long way, there are still a few gaps. See for instance the "Workspace" tab.

$ java -Dawt.useSystemAAFontSettings=on \
       -Dswing.aatext=true \
       -Dswing.defaultlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel \
       -jar /opt/bindiff/bin/bindiff.jar

With the help of a debugger, we can find that when creating a new tab, the color is hardcoded to the WORKSPACE_TAB_COLOR field. With JInterpose, we can interpose to use another field instead, such as java/awt/Color.BLACK.

$ cat example.textproto
action {
	when {
		and {
			expr {
				match {
					classname: "com/google/security/zynamics/bindiff/gui/tabpanels/TabPanelManager"
				}
			}
			expr {
				match {
					methodname: "addTab"
				}
			}
		}
	}
	do {
		field_interposition {
			src_owner: "com/google/security/zynamics/bindiff/gui/tabpanels/TabPanelManager"
			src_name: "WORKSPACE_TAB_COLOR"
			dst_owner: "java/awt/Color"
			dst_name: "BLACK"
		}
	}
}
$ # This is the same command as earlier, but with -javaagent:out/agent.jar=example.textproto to use the agent with the config
$ java -javaagent:out/agent.jar=example.textproto \
       -Dawt.useSystemAAFontSettings=on \
       -Dswing.aatext=true \
       -Dswing.defaultlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel \
       -jar /opt/bindiff/bin/bindiff.jar

This works by applying all the transformations defined in the do section for all the methods matched by the when clause of the config.

For a list of supported actions, see com/pimzero/jinterpose/Proto.proto