472 lines
15 KiB
Python
472 lines
15 KiB
Python
"""
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Utilities for reading and writing Mach-O headers
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"""
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from __future__ import print_function
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import os
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import struct
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import sys
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from macholib.util import fileview
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from .mach_o import (
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FAT_MAGIC,
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FAT_MAGIC_64,
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LC_DYSYMTAB,
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LC_ID_DYLIB,
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LC_LOAD_DYLIB,
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LC_LOAD_UPWARD_DYLIB,
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LC_LOAD_WEAK_DYLIB,
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LC_PREBOUND_DYLIB,
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LC_REEXPORT_DYLIB,
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LC_REGISTRY,
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LC_SEGMENT,
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LC_SEGMENT_64,
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LC_SYMTAB,
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MH_CIGAM,
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MH_CIGAM_64,
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MH_FILETYPE_SHORTNAMES,
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MH_MAGIC,
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MH_MAGIC_64,
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S_ZEROFILL,
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fat_arch,
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fat_arch64,
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fat_header,
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load_command,
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mach_header,
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mach_header_64,
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section,
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section_64,
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)
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from .ptypes import sizeof
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try:
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from macholib.compat import bytes
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except ImportError:
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pass
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try:
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unicode
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except NameError:
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unicode = str
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if sys.version_info[0] == 2:
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range = xrange # noqa: F821
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__all__ = ["MachO"]
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_RELOCATABLE = {
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# relocatable commands that should be used for dependency walking
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LC_LOAD_DYLIB,
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LC_LOAD_UPWARD_DYLIB,
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LC_LOAD_WEAK_DYLIB,
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LC_PREBOUND_DYLIB,
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LC_REEXPORT_DYLIB,
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}
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_RELOCATABLE_NAMES = {
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LC_LOAD_DYLIB: "load_dylib",
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LC_LOAD_UPWARD_DYLIB: "load_upward_dylib",
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LC_LOAD_WEAK_DYLIB: "load_weak_dylib",
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LC_PREBOUND_DYLIB: "prebound_dylib",
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LC_REEXPORT_DYLIB: "reexport_dylib",
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}
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def _shouldRelocateCommand(cmd):
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"""
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Should this command id be investigated for relocation?
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"""
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return cmd in _RELOCATABLE
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def lc_str_value(offset, cmd_info):
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"""
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Fetch the actual value of a field of type "lc_str"
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"""
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cmd_load, cmd_cmd, cmd_data = cmd_info
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offset -= sizeof(cmd_load) + sizeof(cmd_cmd)
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return cmd_data[offset:].strip(b"\x00")
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class MachO(object):
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"""
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Provides reading/writing the Mach-O header of a specific existing file
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"""
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# filename - the original filename of this mach-o
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# sizediff - the current deviation from the initial mach-o size
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# header - the mach-o header
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# commands - a list of (load_command, somecommand, data)
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# data is either a str, or a list of segment structures
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# total_size - the current mach-o header size (including header)
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# low_offset - essentially, the maximum mach-o header size
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# id_cmd - the index of my id command, or None
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def __init__(self, filename):
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# supports the ObjectGraph protocol
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self.graphident = filename
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self.filename = filename
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self.loader_path = os.path.dirname(filename)
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# initialized by load
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self.fat = None
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self.headers = []
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with open(filename, "rb") as fp:
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self.load(fp)
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def __repr__(self):
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return "<MachO filename=%r>" % (self.filename,)
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def load(self, fh):
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assert fh.tell() == 0
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header = struct.unpack(">I", fh.read(4))[0]
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fh.seek(0)
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if header in (FAT_MAGIC, FAT_MAGIC_64):
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self.load_fat(fh)
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else:
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fh.seek(0, 2)
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size = fh.tell()
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fh.seek(0)
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self.load_header(fh, 0, size)
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def load_fat(self, fh):
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self.fat = fat_header.from_fileobj(fh)
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if self.fat.magic == FAT_MAGIC:
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archs = [fat_arch.from_fileobj(fh) for i in range(self.fat.nfat_arch)]
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elif self.fat.magic == FAT_MAGIC_64:
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archs = [fat_arch64.from_fileobj(fh) for i in range(self.fat.nfat_arch)]
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else:
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raise ValueError("Unknown fat header magic: %r" % (self.fat.magic))
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for arch in archs:
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self.load_header(fh, arch.offset, arch.size)
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def rewriteLoadCommands(self, *args, **kw):
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changed = False
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for header in self.headers:
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if header.rewriteLoadCommands(*args, **kw):
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changed = True
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return changed
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def load_header(self, fh, offset, size):
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fh.seek(offset)
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header = struct.unpack(">I", fh.read(4))[0]
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fh.seek(offset)
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if header == MH_MAGIC:
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magic, hdr, endian = MH_MAGIC, mach_header, ">"
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elif header == MH_CIGAM:
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magic, hdr, endian = MH_CIGAM, mach_header, "<"
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elif header == MH_MAGIC_64:
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magic, hdr, endian = MH_MAGIC_64, mach_header_64, ">"
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elif header == MH_CIGAM_64:
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magic, hdr, endian = MH_CIGAM_64, mach_header_64, "<"
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else:
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raise ValueError("Unknown Mach-O header: 0x%08x in %r" % (header, fh))
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hdr = MachOHeader(self, fh, offset, size, magic, hdr, endian)
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self.headers.append(hdr)
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def write(self, f):
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for header in self.headers:
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header.write(f)
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class MachOHeader(object):
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"""
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Provides reading/writing the Mach-O header of a specific existing file
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"""
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# filename - the original filename of this mach-o
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# sizediff - the current deviation from the initial mach-o size
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# header - the mach-o header
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# commands - a list of (load_command, somecommand, data)
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# data is either a str, or a list of segment structures
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# total_size - the current mach-o header size (including header)
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# low_offset - essentially, the maximum mach-o header size
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# id_cmd - the index of my id command, or None
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def __init__(self, parent, fh, offset, size, magic, hdr, endian):
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self.MH_MAGIC = magic
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self.mach_header = hdr
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# These are all initialized by self.load()
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self.parent = parent
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self.offset = offset
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self.size = size
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self.endian = endian
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self.header = None
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self.commands = None
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self.id_cmd = None
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self.sizediff = None
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self.total_size = None
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self.low_offset = None
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self.filetype = None
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self.headers = []
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self.load(fh)
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def __repr__(self):
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return "<%s filename=%r offset=%d size=%d endian=%r>" % (
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type(self).__name__,
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self.parent.filename,
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self.offset,
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self.size,
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self.endian,
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)
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def load(self, fh):
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fh = fileview(fh, self.offset, self.size)
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fh.seek(0)
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self.sizediff = 0
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kw = {"_endian_": self.endian}
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header = self.mach_header.from_fileobj(fh, **kw)
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self.header = header
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# if header.magic != self.MH_MAGIC:
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# raise ValueError("header has magic %08x, expecting %08x" % (
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# header.magic, self.MH_MAGIC))
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cmd = self.commands = []
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self.filetype = self.get_filetype_shortname(header.filetype)
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read_bytes = 0
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low_offset = sys.maxsize
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for i in range(header.ncmds):
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# read the load command
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cmd_load = load_command.from_fileobj(fh, **kw)
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# read the specific command
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klass = LC_REGISTRY.get(cmd_load.cmd, None)
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if klass is None:
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raise ValueError("Unknown load command: %d" % (cmd_load.cmd,))
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cmd_cmd = klass.from_fileobj(fh, **kw)
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if cmd_load.cmd == LC_ID_DYLIB:
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# remember where this command was
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if self.id_cmd is not None:
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raise ValueError("This dylib already has an id")
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self.id_cmd = i
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if cmd_load.cmd in (LC_SEGMENT, LC_SEGMENT_64):
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# for segment commands, read the list of segments
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segs = []
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# assert that the size makes sense
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if cmd_load.cmd == LC_SEGMENT:
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section_cls = section
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else: # LC_SEGMENT_64
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section_cls = section_64
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expected_size = (
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sizeof(klass)
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+ sizeof(load_command)
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+ (sizeof(section_cls) * cmd_cmd.nsects)
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)
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if cmd_load.cmdsize != expected_size:
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raise ValueError("Segment size mismatch")
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# this is a zero block or something
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# so the beginning is wherever the fileoff of this command is
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if cmd_cmd.nsects == 0:
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if cmd_cmd.filesize != 0:
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low_offset = min(low_offset, cmd_cmd.fileoff)
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else:
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# this one has multiple segments
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for _j in range(cmd_cmd.nsects):
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# read the segment
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seg = section_cls.from_fileobj(fh, **kw)
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# if the segment has a size and is not zero filled
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# then its beginning is the offset of this segment
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not_zerofill = (seg.flags & S_ZEROFILL) != S_ZEROFILL
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if seg.offset > 0 and seg.size > 0 and not_zerofill:
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low_offset = min(low_offset, seg.offset)
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if not_zerofill:
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c = fh.tell()
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fh.seek(seg.offset)
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sd = fh.read(seg.size)
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seg.add_section_data(sd)
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fh.seek(c)
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segs.append(seg)
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# data is a list of segments
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cmd_data = segs
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# These are disabled for now because writing back doesn't work
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# elif cmd_load.cmd == LC_CODE_SIGNATURE:
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# c = fh.tell()
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# fh.seek(cmd_cmd.dataoff)
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# cmd_data = fh.read(cmd_cmd.datasize)
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# fh.seek(c)
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# elif cmd_load.cmd == LC_SYMTAB:
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# c = fh.tell()
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# fh.seek(cmd_cmd.stroff)
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# cmd_data = fh.read(cmd_cmd.strsize)
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# fh.seek(c)
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else:
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# data is a raw str
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data_size = cmd_load.cmdsize - sizeof(klass) - sizeof(load_command)
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cmd_data = fh.read(data_size)
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cmd.append((cmd_load, cmd_cmd, cmd_data))
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read_bytes += cmd_load.cmdsize
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# make sure the header made sense
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if read_bytes != header.sizeofcmds:
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raise ValueError(
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"Read %d bytes, header reports %d bytes"
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% (read_bytes, header.sizeofcmds)
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)
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self.total_size = sizeof(self.mach_header) + read_bytes
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self.low_offset = low_offset
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def walkRelocatables(self, shouldRelocateCommand=_shouldRelocateCommand):
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"""
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for all relocatable commands
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yield (command_index, command_name, filename)
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"""
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for (idx, (lc, cmd, data)) in enumerate(self.commands):
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if shouldRelocateCommand(lc.cmd):
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name = _RELOCATABLE_NAMES[lc.cmd]
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ofs = cmd.name - sizeof(lc.__class__) - sizeof(cmd.__class__)
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yield idx, name, data[
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ofs : data.find(b"\x00", ofs) # noqa: E203
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].decode(sys.getfilesystemencoding())
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def rewriteInstallNameCommand(self, loadcmd):
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"""Rewrite the load command of this dylib"""
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if self.id_cmd is not None:
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self.rewriteDataForCommand(self.id_cmd, loadcmd)
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return True
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return False
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def changedHeaderSizeBy(self, bytes):
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self.sizediff += bytes
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if (self.total_size + self.sizediff) > self.low_offset:
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print(
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"WARNING: Mach-O header in %r may be too large to relocate"
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% (self.parent.filename,)
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)
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def rewriteLoadCommands(self, changefunc):
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"""
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Rewrite the load commands based upon a change dictionary
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"""
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data = changefunc(self.parent.filename)
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changed = False
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if data is not None:
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if self.rewriteInstallNameCommand(data.encode(sys.getfilesystemencoding())):
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changed = True
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for idx, _name, filename in self.walkRelocatables():
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data = changefunc(filename)
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if data is not None:
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if self.rewriteDataForCommand(
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idx, data.encode(sys.getfilesystemencoding())
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):
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changed = True
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return changed
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def rewriteDataForCommand(self, idx, data):
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lc, cmd, old_data = self.commands[idx]
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hdrsize = sizeof(lc.__class__) + sizeof(cmd.__class__)
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align = struct.calcsize("Q")
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data = data + (b"\x00" * (align - (len(data) % align)))
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newsize = hdrsize + len(data)
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self.commands[idx] = (lc, cmd, data)
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self.changedHeaderSizeBy(newsize - lc.cmdsize)
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lc.cmdsize, cmd.name = newsize, hdrsize
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return True
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def synchronize_size(self):
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if (self.total_size + self.sizediff) > self.low_offset:
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raise ValueError(
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(
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"New Mach-O header is too large to relocate in %r "
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"(new size=%r, max size=%r, delta=%r)"
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)
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% (
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self.parent.filename,
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self.total_size + self.sizediff,
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self.low_offset,
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self.sizediff,
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)
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)
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self.header.sizeofcmds += self.sizediff
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self.total_size = sizeof(self.mach_header) + self.header.sizeofcmds
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self.sizediff = 0
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def write(self, fileobj):
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fileobj = fileview(fileobj, self.offset, self.size)
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fileobj.seek(0)
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# serialize all the mach-o commands
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self.synchronize_size()
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self.header.to_fileobj(fileobj)
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for lc, cmd, data in self.commands:
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lc.to_fileobj(fileobj)
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cmd.to_fileobj(fileobj)
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if sys.version_info[0] == 2:
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if isinstance(data, unicode):
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fileobj.write(data.encode(sys.getfilesystemencoding()))
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elif isinstance(data, (bytes, str)):
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fileobj.write(data)
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else:
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# segments..
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for obj in data:
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obj.to_fileobj(fileobj)
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else:
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if isinstance(data, str):
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fileobj.write(data.encode(sys.getfilesystemencoding()))
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elif isinstance(data, bytes):
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fileobj.write(data)
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else:
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# segments..
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for obj in data:
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obj.to_fileobj(fileobj)
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# zero out the unused space, doubt this is strictly necessary
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# and is generally probably already the case
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fileobj.write(b"\x00" * (self.low_offset - fileobj.tell()))
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def getSymbolTableCommand(self):
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for lc, cmd, _data in self.commands:
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if lc.cmd == LC_SYMTAB:
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return cmd
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return None
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def getDynamicSymbolTableCommand(self):
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for lc, cmd, _data in self.commands:
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if lc.cmd == LC_DYSYMTAB:
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return cmd
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return None
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def get_filetype_shortname(self, filetype):
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if filetype in MH_FILETYPE_SHORTNAMES:
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return MH_FILETYPE_SHORTNAMES[filetype]
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else:
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return "unknown"
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def main(fn):
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m = MachO(fn)
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seen = set()
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for header in m.headers:
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for _idx, name, other in header.walkRelocatables():
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if other not in seen:
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seen.add(other)
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print("\t" + name + ": " + other)
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if __name__ == "__main__":
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import sys
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files = sys.argv[1:] or ["/bin/ls"]
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for fn in files:
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print(fn)
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main(fn)
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