Give plug-in processes an executable heap and disable PIE/ASLR for Native

build/mac/make_heap_non_executable.py

-#!/usr/bin/python
-
-# Copyright (c) 2011 The Chromium Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-# Usage: make_heap_non_executable.py <executable_path>
-#
-# Arranges for the executable at |executable_path| to have its data (heap)
-# pages protected to prevent execution on Mac OS X 10.7 ("Lion").
-#
-# Traditionally in Mac OS X, 32-bit processes did not have data pages set to
-# prohibit execution. Although user programs could call mprotect and
-# mach_vm_protect to deny execution of code in data pages, the kernel would
-# silently ignore such requests without updating the page tables, and the
-# hardware would happily execute code on such pages. 64-bit processes were
-# always given proper hardware protection of data pages. This behavior was
-# controllable on a system-wide level via the vm.allow_data_exec sysctl, which
-# is set by default to 1. The bit with value 1 (set by default) allows code
-# execution on data pages for 32-bit processes, and the bit with value 2
-# (clear by default) does the same for 64-bit processes.
-#
-# In Mac OS X 10.7, executables can "opt in" to having hardware protection
-# against code execution on data pages applied. This is done by setting a new
-# bit in the |flags| field of an executable's |mach_header|. When
-# MH_NO_HEAP_EXECUTION is set, proper protections will be applied, regardless
-# of the setting of vm.allow_data_exec. See xnu-1699.22.73/osfmk/vm/vm_map.c
-# override_nx and xnu-1699.22.73/bsd/kern/mach_loader.c load_machfile.
-#
-# The Apple toolchain has been revised to set the MH_NO_HEAP_EXECUTION when
-# producing executables, provided that -allow_heap_execute is not specified
-# at link time. Only linkers shipping with Xcode 4.0 and later (ld64-123.2 and
-# later) have this ability. See ld64-123.2.1/src/ld/Options.cpp
-# Options::reconfigureDefaults() and
-# ld64-123.2.1/src/ld/HeaderAndLoadCommands.hpp
-# HeaderAndLoadCommandsAtom<A>::flags().
-#
-# This script sets the MH_NO_HEAP_EXECUTION bit on Mach-O executables. It is
-# intended for use with executables produced by a linker that predates Apple's
-# modifications to set this bit itself. It is also useful for setting this bit
-# for non-i386 executables, including x86_64 executables. Apple's linker only
-# sets it for 32-bit i386 executables, presumably under the assumption that
-# the value of vm.allow_data_exec is set in stone. However, if someone were to
-# change vm.allow_data_exec to 2 or 3, 64-bit x86_64 executables would run
-# without hardware protection against code execution on data pages. This
-# script can set the bit for x86_64 executables, guaranteeing that they run
-# with appropriate protection even when vm.allow_data_exec has been tampered
-# with.
-#
-# This script is able to operate on thin (single-architecture) Mach-O files
-# and fat (universal, multi-architecture) files. When operating on fat files,
-# it will set the MH_NO_HEAP_EXECUTION bit for each architecture contained
-# therein.
-
-
-import os
-import struct
-import sys
-
-
-# <mach-o/fat.h>
-FAT_MAGIC = 0xcafebabe
-FAT_CIGAM = 0xbebafeca
-
-# <mach-o/loader.h>
-MH_MAGIC = 0xfeedface
-MH_CIGAM = 0xcefaedfe
-MH_MAGIC_64 = 0xfeedfacf
-MH_CIGAM_64 = 0xcffaedfe
-MH_EXECUTE = 0x2
-MH_NO_HEAP_EXECUTION = 0x1000000
-
-
-class MachOError(Exception):
-  """A class for exceptions thrown by this module."""
-
-  pass
-
-
-def CheckedSeek(file, offset):
-  """Seeks the file-like object at |file| to offset |offset| and raises a
-  MachOError if anything funny happens."""
-
-  file.seek(offset, os.SEEK_SET)
-  new_offset = file.tell()
-  if new_offset != offset:
-    raise MachOError, \
-          'seek: expected offset %d, observed %d' % (offset, new_offset)
-
-
-def CheckedRead(file, count):
-  """Reads |count| bytes from the file-like |file| object, raising a
-  MachOError if any other number of bytes is read."""
-
-  bytes = file.read(count)
-  if len(bytes) != count:
-    raise MachOError, \
-          'read: expected length %d, observed %d' % (count, len(bytes))
-
-  return bytes
-
-
-def ReadUInt32(file, endian):
-  """Reads an unsinged 32-bit integer from the file-like |file| object,
-  treating it as having endianness specified by |endian| (per the |struct|
-  module), and returns it as a number. Raises a MachOError if the proper
-  length of data can't be read from |file|."""
-
-  bytes = CheckedRead(file, 4)
-
-  (uint32,) = struct.unpack(endian + 'I', bytes)
-  return uint32
-
-
-def ReadMachHeader(file, endian):
-  """Reads an entire |mach_header| structure (<mach-o/loader.h>) from the
-  file-like |file| object, treating it as having endianness specified by
-  |endian| (per the |struct| module), and returns a 7-tuple of its members
-  as numbers. Raises a MachOError if the proper length of data can't be read
-  from |file|."""
-
-  bytes = CheckedRead(file, 28)
-
-  magic, cputype, cpusubtype, filetype, ncmds, sizeofcmds, flags = \
-      struct.unpack(endian + '7I', bytes)
-  return magic, cputype, cpusubtype, filetype, ncmds, sizeofcmds, flags
-
-
-def ReadFatArch(file):
-  """Reads an entire |fat_arch| structure (<mach-o/fat.h>) from the file-like
-  |file| object, treating it as having endianness specified by |endian|
-  (per the |struct| module), and returns a 5-tuple of its members as numbers.
-  Raises a MachOError if the proper length of data can't be read from
-  |file|."""
-
-  bytes = CheckedRead(file, 20)
-
-  cputype, cpusubtype, offset, size, align = struct.unpack('>5I', bytes)
-  return cputype, cpusubtype, offset, size, align
-
-
-def WriteUInt32(file, uint32, endian):
-  """Writes |uint32| as an unsinged 32-bit integer to the file-like |file|
-  object, treating it as having endianness specified by |endian| (per the
-  |struct| module)."""
-
-  bytes = struct.pack(endian + 'I', uint32)
-  assert len(bytes) == 4
-
-  file.write(bytes)
-
-
-def HandleMachOFile(file, offset=0):
-  """Seeks the file-like |file| object to |offset|, reads its |mach_header|,
-  and rewrites the header's |flags| field if appropriate. The header's
-  endianness is detected. Both 32-bit and 64-bit Mach-O headers are supported
-  (mach_header and mach_header_64). Raises MachOError if used on a header that
-  does not have a known magic number or is not of type MH_EXECUTE. The
-  MH_NO_HEAP_EXECUTION is set in the |flags| field and written to |file| if
-  not already set. If already set, nothing is written."""
-
-  CheckedSeek(file, offset)
-  magic = ReadUInt32(file, '<')
-  if magic == MH_MAGIC or magic == MH_MAGIC_64:
-    endian = '<'
-  elif magic == MH_CIGAM or magic == MH_CIGAM_64:
-    endian = '>'
-  else:
-    raise MachOError, \
-          'Mach-O file at offset %d has illusion of magic' % offset
-
-  CheckedSeek(file, offset)
-  magic, cputype, cpusubtype, filetype, ncmds, sizeofcmds, flags = \
-      ReadMachHeader(file, endian)
-  assert magic == MH_MAGIC or magic == MH_MAGIC_64
-  if filetype != MH_EXECUTE:
-    raise MachOError, \
-          'Mach-O file at offset %d is type 0x%x, expected MH_EXECUTE' % \
-              (offset, filetype)
-
-  if not flags & MH_NO_HEAP_EXECUTION:
-    flags |= MH_NO_HEAP_EXECUTION
-    CheckedSeek(file, offset + 24)
-    WriteUInt32(file, flags, endian)
-
-
-def HandleFatFile(file, fat_offset=0):
-  """Seeks the file-like |file| object to |offset| and loops over its
-  |fat_header| entries, calling HandleMachOFile for each."""
-
-  CheckedSeek(file, fat_offset)
-  magic = ReadUInt32(file, '>')
-  assert magic == FAT_MAGIC
-
-  nfat_arch = ReadUInt32(file, '>')
-
-  for index in xrange(0, nfat_arch):
-    cputype, cpusubtype, offset, size, align = ReadFatArch(file)
-    assert size >= 28
-
-    # HandleMachOFile will seek around. Come back here after calling it, in
-    # case it sought.
-    fat_arch_offset = file.tell()
-    HandleMachOFile(file, offset)
-    CheckedSeek(file, fat_arch_offset)
-
-
-def main(me, args):
-  if len(args) != 1:
-    print >>sys.stderr, 'usage: %s <executable_path>' % me
-    return 1
-
-  executable_path = args[0]
-  executable_file = open(executable_path, 'rb+')
-
-  magic = ReadUInt32(executable_file, '<')
-  if magic == FAT_CIGAM:
-    # Check FAT_CIGAM and not FAT_MAGIC because the read was little-endian.
-    HandleFatFile(executable_file)
-  elif magic == MH_MAGIC or magic == MH_CIGAM or \
-      magic == MH_MAGIC_64 or magic == MH_CIGAM_64:
-    HandleMachOFile(executable_file)
-  else:
-    raise MachOError, '%s is not a Mach-O or fat file' % executable_file
-
-  executable_file.close()
-
-  return 0
-
-if __name__ == '__main__':
-  sys.exit(main(sys.argv[0], sys.argv[1:]))