Adding/Finding Places for Instructions - Game Library IDA

Question

Is there any way to add instructions to a library in IDA? My predicament is that there is no room in a game library (.so ELF, android) to fit my own code. There is an empty bss segment but IDA doesn't like to write to it, and I believe the game needs it for it's variables.

I've tried adding additional bytes to the end of the file with a hex editor, and then opening it with IDA, but IDA will not show it possibly because it's not in a segment.

Can I make my own library / modify the existing one so that the code segment is larger? My own library would need to be imported by the other library in order to work, I believe, because it needs functions and such from the original library.

Thanks.

Answer 1

IDA not the most convenient tool for what you're trying to do. There are basically 3 ways to do it, and it seems you're already mentioning all of them in your question :

• Search for a code cave big enough to fit your payload
• Create a new section in your executable with a sufficient size for your payload
• Proxify your library and add functions or hook existing ones

Now depending on what exactly you're trying to inject and how you're reaching it, each method has its specific pro/cons and will require a different approach. They should all be fairly well documented on the Internet.

(Without more context/details about what you're trying to do, it's hard to tell you which one to pick though)