binary patching from Python
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Latest commit 5fe79b7 Jan 10, 2018

README.md

patchkit

Patches an ELF binary using one or more simple Python scripts.

Usage:

patch <binary> <patchdir|file> [patchdir|file...]

patchdir

Contains one or more Python patch files, which will be executed in alphabetical order against a binary.

Patch Examples

Nopping an address, injecting an assembly function, and hooking the entry point:

def simple_patch(pt):
    # nop out a jump at the entry point
    pt.patch(pt.entry, hex='90' * 5)

    # inject assembly into the binary and return the address
    addr = pt.inject(asm='mov eax, 1; ret')

    # hook the entry point to make it call addr (ret will run the original entry point)
    pt.hook(pt.entry, addr)

Replacing a C function:

def replace_free(pt):
    # pretend free() is at this address:
    old_free = 0x804fc4

    # inject a function to replace free()
    new_free = pt.inject(c=r'''
    void free_stub(void *addr) {
        printf("stubbed free(%p)\n", addr);
    }
    ''')

    # patch the beginning of free() with a jump to our new function
    pt.patch(old_free, jmp=new_free)

API

addr = search(data)
hook(addr, new_addr)
patch(addr, *compile arg*)
addr = inject(*compile arg*)

*compile arg* is any of the following:
  raw='data'
  hex='0bfe'
  asm='nop'
  jmp=0xaddr
  c='void func() { int a; a = 1; }' (only supported on inject, not patch)

IDA scripts

Some scripts live in the ida/ path. Run them like this:

/Applications/IDA\ Pro\ 6.8/idaq.app/Contents/MacOS/idaq64 -A -Sida/allfuncs.py a.out

When invoked like this, allfuncs.py will generate a.out.funcs which is used by hardening scripts.

Tools

These are somewhat CGC and x86-specific right now, but will be ported for general use in the future.

  • explore: uses a Python CFG and recursive backtracking emulator to find basic blocks in an executable
  • bindiff: uses the block boundaries from an explore run, as well as additional analysis to find and output basic block diffs between two binaries

Dependencies