elfremove

Toolkit for the removal of symbols from ELF files.

GENERAL

The elfremove toolkit allows the removal of symbols from executable files using the ELF file format. The removal can be achieved by manually providing the symbol names or adresses to be removed or based on the use-case specific analysis data generated from librarytrader.

The toolset requiers python3 and the pyelftools package. For tailoring using the output of librarytrader, the librarytrader module has to be installed on the system or in the virtual environment. If it is not installed, the librarytrader main directory can also be present in the parent directory, next to this directory.

By removing a symbol, all references of it will be wiped from the file, including references in the symbol table sections, hash sections, and any references through relocation section entries. Furthermore, the code of this symbol will be overwritten with '0xCC' bytes.

START-UP

The ELF file is examined for required sections. If the ELF file is super stripped, a fallback to the DYNAMIC Segment is used.

USAGE

The core is the ELFRemove class, which is used by utility scripts implemented in this toolset.

MANUAL REMOVAL

For manual removal we provide the remove_tool.py script.

Usage:

./remove_tool.py <elf file> <Sym1> ... <SymN>

	elf file: The file the given symbols should be removed from.
	SymX:     The symbol names to be removed.

Output:

As a result the removed symbols are listed with detailed information.

USE-CASE REMOVAL

For removal of symbols after a use-case analysis with librarytrader, we additionally provide the remove_tool_libtrader.py script. The script loads a librarystore object created and exported by librarytrader and tailors the included files according to the analysis results.

Usage:

./remove_tool_libtrader.py [-h] [-l] [--lib [LIB ...]] [--libonly] [--overwrite] [--addr_list] [--keep_files] [-v] json

Remove unneccessary symbols of given librarys.

positional arguments:
  json             the json file from libtrader

optional arguments:
  -h, --help       show this help message and exit
  -l, --local      remove local functions
  --lib [LIB ...]  list of librarys to be processed, use all librarys from json file if not defined
  --libonly        name of binary has to start with 'lib'
  --overwrite      overwrite original library files, otherwise work with a copy in the current working directory
  --addr_list      print list of removed locations (addresses) with size
  --keep_files     generate keep files for shrinkelf
  -v, --verbose    set verbosity

Output:

As a result, the removed symbols or the statistics for each file are printed and the tailored files are written into a directory named tailored_libs_<json> (except if the --overwrite flag is used where the files are directly modified in the original location).