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Project description

CLE loads binaries and their associated libraries, resolves imports and provides an abstraction of process memory the same way as if it was loader by the OS's loader.

Installation

$ pip install cle

Usage example

>>> import cle
>>> ld = cle.Loader("/bin/ls")
>>> hex(ld.main_object.entry)
'0x4048d0'
>>> ld.shared_objects
{'ld-linux-x86-64.so.2': <ELF Object ld-2.21.so, maps [0x5000000:0x522312f]>,
 'libacl.so.1': <ELF Object libacl.so.1.1.0, maps [0x2000000:0x220829f]>,
 'libattr.so.1': <ELF Object libattr.so.1.1.0, maps [0x4000000:0x4204177]>,
 'libc.so.6': <ELF Object libc-2.21.so, maps [0x3000000:0x33a1a0f]>,
 'libcap.so.2': <ELF Object libcap.so.2.24, maps [0x1000000:0x1203c37]>}
>>> ld.addr_belongs_to_object(0x5000000)
<ELF Object ld-2.21.so, maps [0x5000000:0x522312f]>
>>> libc_main_reloc = ld.main_object.imports['__libc_start_main']
>>> hex(libc_main_reloc.addr)       # Address of GOT entry for libc_start_main
'0x61c1c0'
>>> import pyvex
>>> some_text_data = ld.memory.load(ld.main_object.entry, 0x100)
>>> irsb = pyvex.lift(some_text_data, ld.main_object.entry, ld.main_object.arch)
>>> irsb.pp()
IRSB {
   t0:Ity_I32 t1:Ity_I32 t2:Ity_I32 t3:Ity_I64 t4:Ity_I64 t5:Ity_I64 t6:Ity_I32 t7:Ity_I64 t8:Ity_I32 t9:Ity_I64 t10:Ity_I64 t11:Ity_I64 t12:Ity_I64 t13:Ity_I64 t14:Ity_I64

   15 | ------ IMark(0x4048d0, 2, 0) ------
   16 | t5 = 32Uto64(0x00000000)
   17 | PUT(rbp) = t5
   18 | t7 = GET:I64(rbp)
   19 | t6 = 64to32(t7)
   20 | t2 = t6
   21 | t9 = GET:I64(rbp)
   22 | t8 = 64to32(t9)
   23 | t1 = t8
   24 | t0 = Xor32(t2,t1)
   25 | PUT(cc_op) = 0x0000000000000013
   26 | t10 = 32Uto64(t0)
   27 | PUT(cc_dep1) = t10
   28 | PUT(cc_dep2) = 0x0000000000000000
   29 | t11 = 32Uto64(t0)
   30 | PUT(rbp) = t11
   31 | PUT(rip) = 0x00000000004048d2
   32 | ------ IMark(0x4048d2, 3, 0) ------
   33 | t12 = GET:I64(rdx)
   34 | PUT(r9) = t12
   35 | PUT(rip) = 0x00000000004048d5
   36 | ------ IMark(0x4048d5, 1, 0) ------
   37 | t4 = GET:I64(rsp)
   38 | t3 = LDle:I64(t4)
   39 | t13 = Add64(t4,0x0000000000000008)
   40 | PUT(rsp) = t13
   41 | PUT(rsi) = t3
   42 | PUT(rip) = 0x00000000004048d6
   43 | t14 = GET:I64(rip)
   NEXT: PUT(rip) = t14; Ijk_Boring
}

Valid options

For a full listing and description of the options that can be provided to the loader and the methods it provides, please examine the docstrings in cle/loader.py. If anything is unclear or poorly documented (there is much) please complain through whatever channel you feel appropriate.

Loading Backends

CLE's loader is implemented in the Loader class. There are several backends that can be used to load a single file:

- ELF, as its name says, loads ELF binaries. ELF files loaded this way are
  statically parsed using PyElfTools.

- PE is a backend to load Microsoft's Portable Executable format,
  effectively Windows binaries. It uses the (optional) `pefile` module.

- Mach-O is a backend to load, you guessed it, Mach-O binaries. It is
  subject to several limitations, which you can read about in the
  [readme in the macho directory](backends/macho/README.md)

- Blob is a backend to load unknown data. It requires that you specify
  the architecture it would be run on, in the form of a class from
  ArchInfo.

Which backend you use can be specified as an argument to Loader. If left unspecified, the loader will pick a reasonable default.

Finding shared libraries

  • If the auto_load_libs option is set to False, the Loader will not automatically load libraries requested by loaded objects. Otherwise...

  • The loader determines which shared objects are needed when loading binaries, and searches for them in the following order:

    • in the current working directory
    • in folders specified in the ld_path option
    • in the same folder as the main binary
    • in the system (in the corresponding library path for the architecture of the binary, e.g., /usr/arm-linux-gnueabi/lib for ARM, note that you need to install cross libraries for this, e.g., libc6-powerpc-cross on Debian - needs emdebian repos)
    • in the system, but with mismatched version numbers from what is specified as a dependency, if the ignore_import_version_numbers option is True
  • If no binary is found with the correct architecture, the loader raises an exception if except_missing_libs option is True. Otherwise it simply leaves the dependencies unresolved.

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