change_mach_o_flags Namespace Reference

Classes
class	MachOError

Functions
def	CheckedSeek (file, offset)
def	CheckedRead (file, count)
def	ReadUInt32 (file, endian)
def	ReadMachHeader (file, endian)
def	ReadFatArch (file)
def	WriteUInt32 (file, uint32, endian)
def	HandleMachOFile (file, options, offset=0)
def	HandleFatFile (file, options, fat_offset=0)
def	main (me, args)

Variables
int	FAT_MAGIC = 0xcafebabe
int	FAT_CIGAM = 0xbebafeca
int	MH_MAGIC = 0xfeedface
int	MH_CIGAM = 0xcefaedfe
int	MH_MAGIC_64 = 0xfeedfacf
int	MH_CIGAM_64 = 0xcffaedfe
int	MH_EXECUTE = 0x2
int	MH_PIE = 0x00200000
int	MH_NO_HEAP_EXECUTION = 0x01000000

Function Documentation

CheckedRead()

def change_mach_o_flags.CheckedRead	(		file,
			count
	)

Reads |count| bytes from the file-like |file| object, raising a
MachOError if any other number of bytes is read.

Definition at line 111 of file change_mach_o_flags.py.

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
 
 

CheckedSeek()

def change_mach_o_flags.CheckedSeek	(		file,
			offset
	)

Seeks the file-like object at |file| to offset |offset| and raises a
MachOError if anything funny happens.

Definition at line 100 of file change_mach_o_flags.py.

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)
 
 

HandleFatFile()

def change_mach_o_flags.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.

Definition at line 219 of file change_mach_o_flags.py.

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)
 
 

HandleMachOFile()

def change_mach_o_flags.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.

Definition at line 173 of file change_mach_o_flags.py.

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)
 
 

main()

def change_mach_o_flags.main	(		me,
			args
	)

Definition at line 240 of file change_mach_o_flags.py.

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
 
 

ReadFatArch()

def change_mach_o_flags.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|.

Definition at line 149 of file change_mach_o_flags.py.

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
 
 

ReadMachHeader()

def change_mach_o_flags.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|.

Definition at line 135 of file change_mach_o_flags.py.

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
 
 

ReadUInt32()

def change_mach_o_flags.ReadUInt32	(		file,
			endian
	)

Reads an unsigned 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|.

Definition at line 123 of file change_mach_o_flags.py.

def ReadUInt32(file, endian):
    """Reads an unsigned 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
 
 

WriteUInt32()

def change_mach_o_flags.WriteUInt32	(		file,
			uint32,
			endian
	)

Writes |uint32| as an unsigned 32-bit integer to the file-like |file|
object, treating it as having endianness specified by |endian| (per the
|struct| module).

Definition at line 162 of file change_mach_o_flags.py.

def WriteUInt32(file, uint32, endian):
    """Writes |uint32| as an unsigned 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)
 
 

Variable Documentation

FAT_CIGAM

int change_mach_o_flags.FAT_CIGAM = 0xbebafeca

Definition at line 82 of file change_mach_o_flags.py.

FAT_MAGIC

int change_mach_o_flags.FAT_MAGIC = 0xcafebabe

Definition at line 81 of file change_mach_o_flags.py.

MH_CIGAM

int change_mach_o_flags.MH_CIGAM = 0xcefaedfe

Definition at line 86 of file change_mach_o_flags.py.

MH_CIGAM_64

int change_mach_o_flags.MH_CIGAM_64 = 0xcffaedfe

Definition at line 88 of file change_mach_o_flags.py.

MH_EXECUTE

int change_mach_o_flags.MH_EXECUTE = 0x2

Definition at line 89 of file change_mach_o_flags.py.

MH_MAGIC

int change_mach_o_flags.MH_MAGIC = 0xfeedface

Definition at line 85 of file change_mach_o_flags.py.

MH_MAGIC_64

int change_mach_o_flags.MH_MAGIC_64 = 0xfeedfacf

Definition at line 87 of file change_mach_o_flags.py.

MH_NO_HEAP_EXECUTION

int change_mach_o_flags.MH_NO_HEAP_EXECUTION = 0x01000000

Definition at line 91 of file change_mach_o_flags.py.

MH_PIE

int change_mach_o_flags.MH_PIE = 0x00200000

Definition at line 90 of file change_mach_o_flags.py.