I'm trying to embed information (a simple integer) inside the executable object file (Elf) of a process in Linux.
I've accomplished that by writing the integer value as binary inside a file, and then by copying the binary file content using the objcopy command.
objcopy --add-section .customsection=binaryfile processElfFile newProcessElfFile
In this way, inside newProcessElfFile I have a perfectly working copy of the process with a new section containing the integer value, and I can see the section by using
readelf -e newProcessElfFile
I have also verified the section value being correct by using some C code on top of the Libelf library. Everything works fine.
Now, I want to read the integer value contained in the new section and perform a printk when the elf file is loaded to be executed.
In order to achieve this, I need to modify the loader code, which is kernel side.
The problem now is that:
- I cannot write code inside the kernel which uses the libelf library, so I cannot access directly the section value as I do with my user-side program.
- The elf kernel loader, contained inside linux-VERSION/fs/binfmt_elf.c, in the function load_elf_binary(), doesn't read elf sections, but access the elf program headers, which point towards elf segments, not the single sections.
In order to solve the problem I guess I need to link my custom section within a segment such that I can access it.
So I have 2 related questions:
- Can I somehow read directly my custom section within the loader?
- If not, How can I make a segment link to the custom section, so that I can access it using the elf file program headers?
Another possibility may be to add the integer value as an element of the already existent .rodata section, but I unfortunately don't know how to perform it and again how to access that section in the kernel.
