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"""golang_loader_assist.py: Help IDA Pro do some golang reversing."""
__author__ = "Tim 'diff' Strazzere"
__copyright__ = "Copyright 2016, Red Naga"
__license__ = "GPL"
__version__ = "1.2"
__email__ = ["strazz@gmail.com"]
from idautils import *
from idc import *
import idaapi
import sys
import string
#
# Constants
#
DEBUG = False
#
# Utility functions
#
def info(formatted_string):
print formatted_string
def error(formatted_string):
print 'ERROR - %s' % formatted_string
def debug(formatted_string):
if DEBUG:
print 'DEBUG - %s' % formatted_string
#
# String defining fuctionality
#
# Indicators of string loads
# mov ebx, offset aWire ; "wire" # Get string
# mov [esp], ebx
# mov dword ptr [esp+4], 4 # String length
# mov ebx, offset unk_8608FD5 # Get string
# mov [esp+8], ebx
# mov dword ptr [esp+0Ch], 0Eh # String length
# mov ebx, offset unk_86006E6 # Get string
# mov [esp+10h], ebx
# mov dword ptr [esp+14h], 5 # String length
# mov ebx, 861143Ch
# mov dword ptr [esp+0F0h+var_E8+4], ebx
# mov [esp+0F0h+var_E0], 19h
# Found in newer versions of golang binaries
# lea rax, unk_8FC736
# mov [rsp+38h+var_18], rax
# mov [rsp+38h+var_10], 1Dh
# lea rdx, unk_8F6E82
# mov [rsp+40h+var_38], rdx
# mov [rsp+40h+var_30], 13h
# lea eax, unk_82410F0
# mov [esp+94h+var_8C], eax
# mov [esp+94h+var_88], 2
# Currently it's normally ebx, but could in theory be anything - seen ebp
VALID_REGS = ['eax', 'ebx', 'ebp', 'rax', 'rcx', 'r10', 'rdx']
# Currently it's normally esp, but could in theory be anything - seen eax
VALID_DEST = ['esp', 'eax', 'ecx', 'edx', 'rsp']
# TODO : Extract patterns
def is_string_load(addr):
patterns = []
# Check for first parts instruction and what it is loading -- also ignore function pointers we may have renamed
if (GetMnem(addr) != 'mov' and GetMnem(addr) != 'lea') and (GetOpType(addr, 1) != 2 or GetOpType(addr, 1) != 5) or GetOpnd(addr, 1)[-4:] == '_ptr':
return False
# Validate that the string offset actually exists inside the binary
if idaapi.get_segm_name(GetOperandValue(addr, 1)) is None:
return False
# Could be unk_, asc_, 'offset ', XXXXh, ignored ones are loc_ or inside []
if GetOpnd(addr, 0) in VALID_REGS and not ('[' in GetOpnd(addr, 1) or 'loc_' in GetOpnd(addr, 1)) and (('offset ' in GetOpnd(addr, 1) or 'h' in GetOpnd(addr, 1)) or ('unk' == GetOpnd(addr, 1)[:3])):
from_reg = GetOpnd(addr, 0)
# Check for second part
addr_2 = FindCode(addr, SEARCH_DOWN)
try:
dest_reg = GetOpnd(addr_2, 0)[GetOpnd(addr_2, 0).index('[') + 1:GetOpnd(addr_2, 0).index('[') + 4]
except ValueError:
return False
if GetMnem(addr_2) == 'mov' and dest_reg in VALID_DEST and ('[%s' % dest_reg) in GetOpnd(addr_2, 0) and GetOpnd(addr_2, 1) == from_reg:
# Check for last part, could be improved
addr_3 = FindCode(addr_2, SEARCH_DOWN)
# GetOpType 1 is a register, potentially we can just check that GetOpType returned 5?
if GetMnem(addr_3) == 'mov' and (('[%s+' % dest_reg) in GetOpnd(addr_3, 0) or GetOpnd(addr_3, 0) in VALID_DEST) and 'offset ' not in GetOpnd(addr_3, 1) and 'dword ptr ds' not in GetOpnd(addr_3, 1) and GetOpType(addr_3, 1) != 1 and GetOpType(addr_3, 1) != 2 and GetOpType(addr_3, 1) != 4:
try:
dumb_int_test = GetOperandValue(addr_3, 1)
if dumb_int_test > 0 and dumb_int_test < sys.maxsize:
return True
except ValueError:
return False
return False
def create_string(addr, string_len):
if idaapi.get_segm_name(addr) is None:
debug('Cannot load a string which has no segment - not creating string @ 0x%02x' % addr)
return False
debug('Found string load @ 0x%x with length of %d' % (addr, string_len))
# This may be overly aggressive if we found the wrong area...
if GetStringType(addr) is not None and GetString(addr) is not None and len(GetString(addr)) != string_len:
debug('It appears that there is already a string present @ 0x%x' % addr)
MakeUnknown(addr, string_len, DOUNK_SIMPLE)
if GetString(addr) is None and MakeStr(addr, addr + string_len):
return True
else:
# If something is already partially analyzed (incorrectly) we need to MakeUnknown it
MakeUnknown(addr, string_len, DOUNK_SIMPLE)
if MakeStr(addr, addr + string_len):
return True
debug('Unable to make a string @ 0x%x with length of %d' % (addr, string_len))
return False
def create_offset(addr):
if OpOff(addr, 1, 0):
return True
else:
debug('Unable to make an offset for string @ 0x%x ' % addr)
return False
def strings_init():
strings_added = 0
retry = []
text_seg = get_text_seg()
if text_seg is None:
debug('Failed to get text segment')
return strings_added
# This may be inherently flawed as it will only search for defined functions
# and as of IDA Pro 6.95 it fails to autoanalyze many GO functions, currently
# this works well since we redefine/find (almost) all the functions prior to
# this being used. Could be worth a strategy rethink later one or on diff archs
for addr in Functions(text_seg.startEA, text_seg.endEA):
name = GetFunctionName(addr)
end_addr = Chunks(addr).next()[1]
if(end_addr < addr):
error('Unable to find good end for the function %s' % name)
pass
debug('Found function %s starting/ending @ 0x%x 0x%x' % (name, addr, end_addr))
while addr <= end_addr:
if is_string_load(addr):
if 'rodata' not in idaapi.get_segm_name(addr) and 'text' not in idaapi.get_segm_name(addr):
debug('Should a string be in the %s section?' % idaapi.get_segm_name(addr))
string_addr = GetOperandValue(addr, 1)
addr_3 = FindCode(FindCode(addr, SEARCH_DOWN), SEARCH_DOWN)
string_len = GetOperandValue(addr_3, 1)
if create_string(string_addr, string_len):
if create_offset(addr):
strings_added += 1
else:
# There appears to be something odd that goes on with IDA making some strings, always works
# the second time, so lets just force a retry...
retry.append((addr, string_addr, string_len))
# Skip the extra mov lines since we know it won't be a load on any of them
addr = FindCode(addr_3, SEARCH_DOWN)
else:
addr = FindCode(addr, SEARCH_DOWN)
for instr_addr, string_addr, string_len in retry:
if create_string(string_addr, string_len):
if create_offset(instr_addr):
strings_added += 1
else:
error('Unable to make a string @ 0x%x with length of %d for usage in function @ 0x%x' % (string_addr, string_len, instr_addr))
return strings_added
#
# Function defining methods
#
def get_text_seg():
# .text found in PE & ELF binaries, __text found in macho binaries
return _get_seg(['.text', '__text'])
def get_gopclntab_seg():
# .gopclntab found in PE & ELF binaries, __gopclntab found in macho binaries
return _get_seg(['.gopclntab', '__gopclntab'])
def _get_seg(possible_seg_names):
seg = None
for seg_name in possible_seg_names:
seg = idaapi.get_segm_by_name(seg_name)
if seg:
return seg
return seg
# Indicators of runtime_morestack
# mov large dword ptr ds:1003h, 0 # most I've seen
# mov qword ptr ds:1003h, 0 # some
def is_simple_wrapper(addr):
if GetMnem(addr) == 'xor' and GetOpnd(addr, 0) == 'edx' and GetOpnd(addr, 1) == 'edx':
addr = FindCode(addr, SEARCH_DOWN)
if GetMnem(addr) == 'jmp' and GetOpnd(addr, 0) == 'runtime_morestack':
return True
return False
def create_runtime_ms():
debug('Attempting to find runtime_morestack function for hooking on...')
text_seg = get_text_seg()
if text_seg is None:
debug('Failed to get text segment')
return None
# Opcodes for "mov large dword ptr ds:1003h, 0", binary search is faster than text search
opcodes = 'c7 05 03 10 00 00 00 00 00 00'
if idaapi.get_inf_structure().is_64bit():
# Opcodes for "mov qword ptr ds:dword_1000+3, 0"
opcodes = '48 c7 04 25 03 10 00 00 00 00 00 00'
runtime_ms_end = idaapi.find_binary(text_seg.startEA, text_seg.endEA, opcodes, 0, SEARCH_DOWN)
if runtime_ms_end == BADADDR:
debug('Failed to find opcodes associated with runtime_morestack: %s' % opcodes)
return None
runtime_ms = idaapi.get_func(runtime_ms_end)
if runtime_ms is None:
debug('Failed to get runtime_morestack function from address @ 0x%x' % runtime_ms_end)
return None
if idc.MakeNameEx(runtime_ms.startEA, "runtime_morestack", SN_PUBLIC):
debug('Successfully found runtime_morestack')
else:
debug('Failed to rename function @ 0x%x to runtime_morestack' % runtime_ms.startEA)
return runtime_ms
def traverse_xrefs(func):
func_created = 0
if func is None:
return func_created
# First
func_xref = idaapi.get_first_cref_to(func.startEA)
# Attempt to go through crefs
while func_xref != BADADDR:
# See if there is a function already here
if idaapi.get_func(func_xref) is None:
# Ensure instruction bit looks like a jump
func_end = FindCode(func_xref, SEARCH_DOWN)
if GetMnem(func_end) == "jmp":
# Ensure we're jumping back "up"
func_start = GetOperandValue(func_end, 0)
if func_start < func_xref:
if idc.MakeFunction(func_start, func_end):
func_created += 1
else:
# If this fails, we should add it to a list of failed functions
# Then create small "wrapper" functions and backtrack through the xrefs of this
error('Error trying to create a function @ 0x%x - 0x%x' %(func_start, func_end))
else:
xref_func = idaapi.get_func(func_xref)
# Simple wrapper is often runtime_morestack_noctxt, sometimes it isn't though...
if is_simple_wrapper(xref_func.startEA):
debug('Stepping into a simple wrapper')
func_created += traverse_xrefs(xref_func)
if idaapi.get_func_name(xref_func.startEA) is not None and 'sub_' not in idaapi.get_func_name(xref_func.startEA):
debug('Function @0x%x already has a name of %s; skipping...' % (func_xref, idaapi.get_func_name(xref_func.startEA)))
else:
debug('Function @ 0x%x already has a name %s' % (xref_func.startEA, idaapi.get_func_name(xref_func.startEA)))
func_xref = idaapi.get_next_cref_to(func.startEA, func_xref)
return func_created
def find_func_by_name(name):
text_seg = get_text_seg()
if text_seg is None:
return None
for addr in Functions(text_seg.startEA, text_seg.endEA):
if name == idaapi.get_func_name(addr):
return idaapi.get_func(addr)
return None
def runtime_init():
func_created = 0
if find_func_by_name('runtime_morestack') is not None:
func_created += traverse_xrefs(find_func_by_name('runtime_morestack'))
func_created += traverse_xrefs(find_func_by_name('runtime_morestack_noctxt'))
else:
runtime_ms = create_runtime_ms()
func_created = traverse_xrefs(runtime_ms)
return func_created
#
# Function renaming fuctionality
#
def create_pointer(addr, force_size=None):
if force_size is not 4 and (idaapi.get_inf_structure().is_64bit() or force_size is 8):
MakeQword(addr)
return Qword(addr), 8
else:
MakeDword(addr)
return Dword(addr), 4
STRIP_CHARS = [ '(', ')', '[', ']', '{', '}', ' ', '"' ]
REPLACE_CHARS = ['.', '*', '-', ',', ';', ':', '/', '\xb7' ]
def clean_function_name(str):
# Kill generic 'bad' characters
str = filter(lambda x: x in string.printable, str)
for c in STRIP_CHARS:
str = str.replace(c, '')
for c in REPLACE_CHARS:
str = str.replace(c, '_')
return str
def renamer_init():
renamed = 0
gopclntab = get_gopclntab_seg()
if gopclntab is not None:
# Skip unimportant header and goto section size
addr = gopclntab.startEA + 8
size, addr_size = create_pointer(addr)
addr += addr_size
# Unsure if this end is correct
early_end = addr + (size * addr_size * 2)
while addr < early_end:
func_offset, addr_size = create_pointer(addr)
name_offset, addr_size = create_pointer(addr + addr_size)
addr += addr_size * 2
func_name_addr = Dword(name_offset + gopclntab.startEA + addr_size) + gopclntab.startEA
func_name = GetString(func_name_addr)
MakeStr(func_name_addr, func_name_addr + len(func_name))
appended = clean_func_name = clean_function_name(func_name)
debug('Going to remap function at 0x%x with %s - cleaned up as %s' % (func_offset, func_name, clean_func_name))
if idaapi.get_func_name(func_offset) is not None:
if MakeName(func_offset, clean_func_name):
renamed += 1
else:
error('clean_func_name error %s' % clean_func_name)
return renamed
# Function pointers are often used instead of passing a direct address to the
# function -- this function names them based off what they're currently named
# to ease reading
#
# lea rax, main_GetExternIP_ptr <-- pointer to actual function
# mov [rsp+1C0h+var_1B8], rax <-- loaded as arg for next function
# call runtime_newproc <-- function is used inside a new process
def pointer_renamer():
renamed = 0
text_seg = get_text_seg()
if text_seg is None:
debug('Failed to get text segment')
return renamed
for addr in Functions(text_seg.startEA, text_seg.endEA):
name = GetFunctionName(addr)
# Look at data xrefs to the function - find the pointer that is located in .rodata
data_ref = idaapi.get_first_dref_to(addr)
while data_ref != BADADDR:
if 'rodata' in idaapi.get_segm_name(data_ref):
# Only rename things that are currently listed as an offset; eg. off_9120B0
if 'off_' in GetTrueName(data_ref):
if MakeName(data_ref, ('%s_ptr' % name)):
renamed += 1
else:
error('error attempting to name pointer @ 0x%02x for %s' % (data_ref, name))
data_ref = idaapi.get_next_dref_to(addr, data_ref)
return renamed
def main():
# This should be run before the renamer, as it will find and help define more functions
func_added = runtime_init()
info('Found and successfully created %d functions!' % func_added)
# This should prevent the script from locking up due to the auto initalizer
idaapi.autoWait()
# Should be run after the function initializer,
renamed = renamer_init()
info('Found and successfully renamed %d functions!' % renamed)
# Attempt to rename all function pointers after we have all the functions and proper function names
pointers_renamed = pointer_renamer()
info('Found and successfully renamed %d function pointers!' % pointers_renamed)
# Attempt to find all string loading idioms
strings_added = strings_init()
info('Found and successfully created %d strings!' % strings_added)
if __name__ == "__main__":
main()