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

Client loader processes.

Some plug-ins depend on having an executable heap. They write code to data
pages and attempt to execute it without calling mprotect to mark this code
as executable.

Native Client needs to allocate a contiguous 1GB of address space. ASLR may
interfere with there being a "hole" this large in the address space by the
time NaCl makes its request.

Non-executable heaps are only available in 10.7 and later for 32-bit
processes.

PIE/ASLR was formerly disabled for all processes other than the browser
process. This change reenables it for all processes other than the NaCl
loader. PIE/ASLR is available on 10.5 and later, although the implementation
is stronger in 10.7 than in earlier releases.

This change results in two new helpers in addition to the existing
Chromium Helper.app: Chromium Helper EH.app (for executable heaps) and
Chromium Helper NP.app (for no PIE). libplugin_carbon_interpose.dylib moves
out of the helper .app and directly into the versioned directory. The
InfoPlist.strings have been removed from the helper app, but empty .lproj
directories remain.

BUG=90221, 93551
TEST=everything
Review URL: http://codereview.chromium.org/7714018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@97984 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 274 insertions, 0 deletions

diff --git a/build/mac/change_mach_o_flags.py b/build/mac/change_mach_o_flags.py
new file mode 100755
index 0000000..1dfe07f
--- /dev/null
+++ b/build/mac/change_mach_o_flags.py
@@ -0,0 +1,274 @@
+#!/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: change_mach_o_flags.py [--executable-heap] [--no-pie] <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"), and to have
+# the PIE (position independent executable) bit set to enable ASLR (address
+# space layout randomization). With --executable-heap or --no-pie, the
+# respective bits are cleared instead of set, making the heap executable or
+# disabling PIE/ASLR.
+#
+# 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 or clear the bits for each architecture contained therein.
+#
+# NON-EXECUTABLE HEAP
+#
+# 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.
+#
+# POSITION-INDEPENDENT EXECUTABLES/ADDRESS SPACE LAYOUT RANDOMIZATION
+#
+# This script sets or clears the MH_PIE bit in an executable's Mach-O header,
+# enabling or disabling position independence on Mac OS X 10.5 and later.
+# Processes running position-independent executables have varying levels of
+# ASLR protection depending on the OS release. The main executable's load
+# address, shared library load addresess, and the heap and stack base
+# addresses may be randomized. Position-independent executables are produced
+# by supplying the -pie flag to the linker (or defeated by supplying -no_pie).
+# Executables linked with a deployment target of 10.7 or higher have PIE on
+# by default.
+#
+# This script is never strictly needed during the build to enable PIE, as all
+# linkers used are recent enough to support -pie. However, it's used to
+# disable the PIE bit as needed on already-linked executables.
+
+
+import optparse
+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_PIE = 0x00200000
+MH_NO_HEAP_EXECUTION = 0x01000000
+
+
+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, options, 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_PIE and MH_NO_HEAP_EXECUTION bits are set or cleared in the |flags| field
+  according to |options| and written to |file| if any changes need to be made.
+  If already set or clear as specified by |options|, 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)
+
+  original_flags = flags
+
+  if options.no_heap_execution:
+    flags |= MH_NO_HEAP_EXECUTION
+  else:
+    flags &= ~MH_NO_HEAP_EXECUTION
+
+  if options.pie:
+    flags |= MH_PIE
+  else:
+    flags &= ~MH_PIE
+
+  if flags != original_flags:
+    CheckedSeek(file, offset + 24)
+    WriteUInt32(file, flags, endian)
+
+
+def HandleFatFile(file, options, 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, options, offset)
+    CheckedSeek(file, fat_arch_offset)
+
+
+def main(me, args):
+  parser = optparse.OptionParser('%prog [options] <executable_path>')
+  parser.add_option('--executable-heap', action='store_false',
+                    dest='no_heap_execution', default=True,
+                    help='Clear the MH_NO_HEAP_EXECUTION bit')
+  parser.add_option('--no-pie', action='store_false',
+                    dest='pie', default=True,
+                    help='Clear the MH_PIE bit')
+  (options, loose_args) = parser.parse_args(args)
+  if len(loose_args) != 1:
+    parser.print_usage()
+    return 1
+
+  executable_path = loose_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, options)
+  elif magic == MH_MAGIC or magic == MH_CIGAM or \
+      magic == MH_MAGIC_64 or magic == MH_CIGAM_64:
+    HandleMachOFile(executable_file, options)
+  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:]))