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get_cfg.py
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#!/usr/bin/env python
# Copyright (c) 2017 Trail of Bits, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import idautils
import idaapi
import idc
import sys
import os
import argparse
import struct
import traceback
import collections
import itertools
import pprint
# Bring in utility libraries.
from util import *
from table import *
from flow import *
from refs import *
from segment import *
from collect_variable import *
from exception import *
#hack for IDAPython to see google protobuf lib
if os.path.isdir('/usr/lib/python2.7/dist-packages'):
sys.path.append('/usr/lib/python2.7/dist-packages')
if os.path.isdir('/usr/local/lib/python2.7/dist-packages'):
sys.path.append('/usr/local/lib/python2.7/dist-packages')
tools_disass_ida_dir = os.path.dirname(__file__)
tools_disass_dir = os.path.dirname(tools_disass_ida_dir)
# Note: The bootstrap file will copy CFG_pb2.py into this dir!!
import CFG_pb2
EXTERNAL_FUNCS_TO_RECOVER = {}
EXTERNAL_VARS_TO_RECOVER = {}
RECOVERED_EAS = set()
ACCESSED_VIA_JMP = set()
TO_RECOVER = {
"stack_var" : False,
}
# Map of external functions names to a tuple containing information like the
# number of arguments and calling convention of the function.
EMAP = {}
# Map of external variable names to their sizes, in bytes.
EMAP_DATA = {}
# `True` if we are getting the CFG of a position independent executable. This
# affects heuristics like trying to turn immediate operands in instructions
# into references into the data.
PIE_MODE = False
# Name of the operating system that runs the program being lifted. E.g. if
# we're lifting an ELF then this will typically be `linux`.
OS_NAME = ""
# Set of substrings that can be found inside of symbol names that are usually
# signs that the symbol is external. For example, `stderr@@GLIBC_2.2.5` is
# really the external `stderr`, so we want to be able to chop out the `@@...`
# part to resolve the "true" name. There are a lot of `@@` variants in PE files,
# e.g. `@@QEAU_..`, `@@AEAV..`, though these are likely for name mangling.
EXTERNAL_NAMES = ("@@GLIBC_", )
_NOT_ELF_BEGIN_EAS = (0xffffffffL, 0xffffffffffffffffL)
# Returns `True` if this is an ELF binary (as opposed to an ELF object file).
def is_linked_ELF_program():
global _NOT_ELF_BEGIN_EAS
return IS_ELF and idc.BeginEA() not in _NOT_ELF_BEGIN_EAS
def is_ELF_got_pointer(ea):
"""Returns `True` if this is a pointer to a pointer stored in the
`.got` section of an ELF binary. For example, `__gmon_start___ptr` is
a pointer in the `.got` that will be fixed up to contain the address of
the external function `__gmon_start__`. We don't want to treat
`__gmon_start___ptr` as external because it is really a sort of local
variable that will will resolve with a data cross-reference."""
seg_name = idc.SegName(ea).lower()
if ".got" not in seg_name:
return False
name = get_symbol_name(ea)
if not name.endswith("_ptr"):
return False
target_ea = get_reference_target(ea)
target_name = get_true_external_name(get_symbol_name(target_ea))
if target_name not in name:
return False
return is_referenced_by(target_ea, ea)
def is_ELF_got_pointer_to_external(ea):
"""Similar to `is_ELF_got_pointer`, but requires that the eventual target
of the pointer is an external."""
if not is_ELF_got_pointer(ea):
return False
target_ea = get_reference_target(ea)
return is_external_segment(target_ea)
_FIXED_EXTERNAL_NAMES = {}
def demangled_name(name):
"""Tries to demangle a functin name."""
try:
dname = idc.Demangle(name, idc.GetLongPrm(INF_SHORT_DN))
if dname and len(dname) and "::" not in dname:
dname = dname.split("(")[0]
dname = dname.split(" ")[-1]
if re.match(r"^[a-zA-Z0-9_]+$", dname):
return dname
return name
except:
return name
def get_true_external_name(fn, demangle=True):
"""Tries to get the 'true' name of `fn`. This removes things like
ELF-versioning from symbols."""
if not fn:
return ""
orig_fn = fn
if fn in _FIXED_EXTERNAL_NAMES:
return _FIXED_EXTERNAL_NAMES[orig_fn]
if fn in EMAP:
return fn
if fn in EMAP_DATA:
return fn
# Try to demangle the name, but don't do it if looks like there's a C++
# namespace.
if demangle:
fn = demangled_name(fn)
# TODO(pag): Is this a macOS or Windows thing?
if not is_linked_ELF_program() and fn[0] == '_':
return fn[1:]
if fn.endswith("_0"):
newfn = fn[:-2]
if newfn in EMAP:
return newfn
# Go and strip off things like the `@@GLIBC_*` symbol suffixes.
for en in EXTERNAL_NAMES:
if en in fn:
fn = fn[:fn.find(en)]
break
if orig_fn != fn:
DEBUG("True name of {} is {}".format(orig_fn, fn))
_FIXED_EXTERNAL_NAMES[orig_fn] = fn
return fn
# Set of symbols that IDA identifies as being "weak" symbols. In ELF binaries,
# a weak symbol is kind of an optional linking thing. For example, the
# `__gmon_start__` function is referenced as a weak symbol. This function is
# used for gcov-based profiling. If gcov is available, then this symbol will
# be resolved to a real function, but if not, it will be NULL and programs
# will detect it as such. An example use of a weak symbol in C would be:
#
# extern void __gmon_start__(void) __attribute__((weak));
# ...
# if (__gmon_start__) {
# __gmon_start__();
# }
WEAK_SYMS = set()
# Used to track thunks that are actually implemented. For example, in a static
# binary, you might have a bunch of calls to `strcpy` in the `.plt` section
# that go through the `.plt.got` to call the implementation of `strcpy` compiled
# into the binary.
INTERNALLY_DEFINED_EXTERNALS = {} # Name external to EA of internal.
INTERNAL_THUNK_EAS = {} # EA of thunk to EA of implementation.
def parse_os_defs_file(df):
"""Parse the file containing external function and variable
specifications."""
global OS_NAME, WEAK_SYMS, EMAP, EMAP_DATA
global _FIXED_EXTERNAL_NAMES, INTERNALLY_DEFINED_EXTERNALS
is_linux = OS_NAME == "linux"
for l in df.readlines():
#skip comments / empty lines
l = l.strip()
if not l or l[0] == "#":
continue
if l.startswith('DATA:'):
# process as data
(marker, symname, dsize) = l.split()
if 'PTR' in dsize:
dsize = get_address_size_in_bytes()
EMAP_DATA[symname] = int(dsize)
else:
fname = args = conv = ret = sign = None
line_args = l.split()
if len(line_args) == 4:
(fname, args, conv, ret) = line_args
elif len(line_args) == 5:
(fname, args, conv, ret, sign) = line_args
if conv == "C":
realconv = CFG_pb2.ExternalFunction.CallerCleanup
elif conv == "E":
realconv = CFG_pb2.ExternalFunction.CalleeCleanup
elif conv == "F":
realconv = CFG_pb2.ExternalFunction.FastCall
else:
DEBUG("ERROR: Unknown calling convention: {}".format(l))
continue
if ret not in "YN":
DEBUG("ERROR: Unknown return type {} in {}".format(ret, l))
continue
ea = idc.LocByName(fname)
if not is_invalid_ea(ea):
if not is_external_segment(ea) and not is_thunk(ea):
DEBUG("Not treating {} as external, it is defined at {:x}".format(
fname, ea))
INTERNALLY_DEFINED_EXTERNALS[fname] = ea
continue
# Misidentified and external. This comes up often in PE binaries, for
# example, we will have the following:
#
# .idata:01400110E8 ; void __stdcall EnterCriticalSection(...)
# .idata:01400110E8 extrn EnterCriticalSection:qword
#
# Really, we want to try this as code.
flags = idc.GetFlags(ea)
if not idc.isCode(flags) and not idaapi.is_weak_name(ea):
seg_name = idc.SegName(ea).lower()
if ".idata" in seg_name:
EXTERNAL_FUNCS_TO_RECOVER[ea] = fname
# Refer to issue #308
else:
DEBUG("WARNING: External {} at {:x} from definitions file may not be a function".format(
fname, ea))
EMAP[fname] = (int(args), realconv, ret, sign)
# Sometimes there will be things like `__imp___gmon_start__` which
# is really the implementation of `__gmon_start__`, where that is
# a weak symbol.
if is_linux:
imp_name = "__imp_{}".format(fname)
if idc.LocByName(imp_name):
_FIXED_EXTERNAL_NAMES[imp_name] = fname
WEAK_SYMS.add(fname)
WEAK_SYMS.add(imp_name)
df.close()
def is_external_reference(ea):
"""Returns `True` if `ea` references external data."""
return is_external_segment(ea) \
or ea in EXTERNAL_VARS_TO_RECOVER \
or ea in EXTERNAL_FUNCS_TO_RECOVER
def get_function_name(ea):
"""Return name of a function, as IDA sees it. This includes allowing
dummy names, e.g. `sub_abc123`."""
return get_symbol_name(ea, ea, allow_dummy=True)
def undecorate_external_name(fn):
# Don't mangle symbols for fully linked ELFs... yet
in_a_map = fn in EMAP or fn in EMAP_DATA
if not is_linked_ELF_program():
if fn.startswith("__imp_"):
fn = fn[6:]
if fn.endswith("_0"):
fn = fn[:-2]
# name could have been modified by the above tests
in_a_map = fn in EMAP or fn in EMAP_DATA
if fn.startswith("_") and not in_a_map:
fn = fn[1:]
if fn.startswith("@") and not in_a_map:
fn = fn[1:]
if IS_ELF and '@' in fn:
fn = fn[:fn.find('@')]
fixfn = get_true_external_name(fn)
return fixfn
_ELF_THUNKS = {}
_NOT_ELF_THUNKS = set()
_INVALID_THUNK = (False, idc.BADADDR, "")
_INVALID_THUNK_ADDR = (False, idc.BADADDR)
def is_ELF_thunk_by_structure(ea):
"""Try to manually identify an ELF thunk by its structure."""
global _INVALID_THUNK_ADDR
if ".plt" not in idc.SegName(ea).lower():
return _INVALID_THUNK_ADDR
# Scan through looking for a branch, either direct or indirect.
inst = None
for i in range(4): # 1 is good enough for x86, 4 for aarch64.
inst, _ = decode_instruction(ea)
if not inst:
return _INVALID_THUNK_ADDR
# elif is_direct_jump(inst):
# ea = get_direct_branch_target(inst)
# inst = None
elif is_indirect_jump(inst) or is_direct_jump(inst):
ea = inst.ea
break
else:
ea = inst.ea + inst.size
inst = None
if not inst:
return _INVALID_THUNK_ADDR
target_ea = get_reference_target(inst.ea)
if ".got.plt" == idc.SegName(target_ea).lower():
target_ea = get_reference_target(target_ea)
# For AArch64, the thunk structure is something like:
# .plt:000400470 .atoi
# .plt:000400470 ADRP X16, #off_411000@PAGE
# .plt:000400474 LDR X17, [X16,#off_411000@PAGEOFF]
# .plt:000400478 ADD X16, X16, #off_411000@PAGEOFF
# .plt:00040047C BR X17 ; atoi
#
# With:
#
# extern:000411070 ; int atoi(const char *nptr)
# extern:000411070 IMPORT atoi
# For x86, the thunk structure is something like:
#
# .plt:00041F10 _qsort proc near
# .plt:00041F10 jmp cs:off_31F388
# .plt:00041F10 _qsort endp
#
# With:
#
# .got.plt:0031F388 off_31F388 dq offset qsort
#
# With
# extern:0031F388 ; void qsort(void *base, ...)
# extern:0031F388 extrn qsort:near
if is_invalid_ea(target_ea):
return _INVALID_THUNK_ADDR
return True, target_ea
def is_thunk_by_flags(ea):
"""Try to identify a thunk based off of the IDA flags. This isn't actually
specific to ELFs.
IDA seems to have a kind of thunk-propagation. So if one thunk calls
another thunk, then the former thing is treated as a thunk. The former
thing will not actually follow the 'structured' form matched above, so
we'll try to recursively match to the 'final' referenced thunk."""
global _INVALID_THUNK_ADDR
if not is_thunk(ea):
return _INVALID_THUNK_ADDR
ea_name = get_function_name(ea)
inst, _ = decode_instruction(ea)
if not inst:
DEBUG("WARNING: {} at {:x} is a thunk with no code??".format(ea_name, ea))
return _INVALID_THUNK_ADDR
# Recursively find thunk-to-thunks.
if is_direct_jump(inst) or is_direct_function_call(inst):
targ_ea = get_direct_branch_target(inst)
targ_is_thunk = is_thunk(targ_ea)
if targ_is_thunk:
targ_thunk_name = get_symbol_name(ea, targ_ea)
DEBUG("Found thunk-to-thunk {:x} -> {:x}: {} to {}".format(
ea, targ_ea, ea_name, targ_thunk_name))
return True, targ_ea
DEBUG("ERROR? targ_ea={:x} is not thunk".format(targ_ea))
if not is_external_reference(ea):
return _INVALID_THUNK_ADDR
return True, targ_ea
def try_get_thunk_name(ea):
"""Try to figure out if a function is actually a thunk, i.e. a function
that represents a 'local' definition for an external function. Thunks work
by having the local function jump through a function pointer that is
resolved at runtime."""
global _ELF_THUNKS, _NOT_ELF_THUNKS, _INVALID_THUNK
if ea in _ELF_THUNKS:
return _ELF_THUNKS[ea]
if ea in _NOT_ELF_THUNKS:
_NOT_ELF_THUNKS.add(ea)
return _INVALID_THUNK
# Try two approaches to detecting whether or not
# something is a thunk.
is_thunk = False
target_ea = idc.BADADDR
if IS_ELF:
is_thunk, target_ea = is_ELF_thunk_by_structure(ea)
if not is_thunk:
is_thunk, target_ea = is_thunk_by_flags(ea)
if not is_thunk:
_NOT_ELF_THUNKS.add(ea)
return _INVALID_THUNK
else:
name = get_function_name(target_ea)
name = undecorate_external_name(name)
name = get_true_external_name(name)
ret = (is_thunk, target_ea, name)
_ELF_THUNKS[ea] = ret
return ret
def is_start_of_function(ea):
"""Returns `True` if `ea` is the start of a function."""
if not is_code(ea):
return False
name = idc.GetFunctionName(ea) or idc.GetTrueName(ea)
return ea == idc.LocByName(name)
_REFERENCE_OPERAND_TYPE = {
Reference.IMMEDIATE: CFG_pb2.CodeReference.ImmediateOperand,
Reference.DISPLACEMENT: CFG_pb2.CodeReference.MemoryDisplacementOperand,
Reference.MEMORY: CFG_pb2.CodeReference.MemoryOperand,
Reference.CODE: CFG_pb2.CodeReference.ControlFlowOperand,
}
def reference_target_type(ref):
"""Sometimes code references into the GOT would be treated as data
references. We fall back onto our external maps as an oracle for
what the type should really be. This has happened with `pcre_free`
references from Apache."""
if ref.ea in EXTERNAL_VARS_TO_RECOVER:
return CFG_pb2.CodeReference.DataTarget
# TODO(pag):
#elif ref.ea in EXTERNAL_FUNCS_TO_RECOVER:
# return CFG_pb2.CodeReference.CodeTarget
elif is_code(ref.ea):
return CFG_pb2.CodeReference.CodeTarget
else:
return CFG_pb2.CodeReference.DataTarget
def reference_operand_type(ref):
global _REFERENCE_OPERAND_TYPE
return _REFERENCE_OPERAND_TYPE[ref.type]
def reference_location(ref):
if ref.ea in EXTERNAL_VARS_TO_RECOVER:
return CFG_pb2.CodeReference.External
elif ref.ea in EXTERNAL_FUNCS_TO_RECOVER:
return CFG_pb2.CodeReference.External
elif is_external_segment_by_flags(ref.ea):
DEBUG("WARNING: Reference to {:x} is in an external segment, but is not an external var or function".format(ref.ea))
return CFG_pb2.CodeReference.External
else:
return CFG_pb2.CodeReference.Internal
def referenced_name(ref):
if ref.ea in EXTERNAL_VARS_TO_RECOVER:
return EXTERNAL_VARS_TO_RECOVER[ref.ea]
elif ref.ea in EXTERNAL_FUNCS_TO_RECOVER:
return EXTERNAL_FUNCS_TO_RECOVER[ref.ea]
else:
return get_true_external_name(ref.symbol)
_TARGET_NAME = {
CFG_pb2.CodeReference.CodeTarget: "code",
CFG_pb2.CodeReference.DataTarget: "data",
}
_OPERAND_NAME = {
CFG_pb2.CodeReference.ImmediateOperand: "imm",
CFG_pb2.CodeReference.MemoryDisplacementOperand: "disp",
CFG_pb2.CodeReference.MemoryOperand: "mem",
CFG_pb2.CodeReference.ControlFlowOperand: "flow",
}
_LOCATION_NAME = {
CFG_pb2.CodeReference.External: "external",
CFG_pb2.CodeReference.Internal: "internal",
}
def format_instruction_reference(ref):
"""Returns a string representation of a cross reference contained
in an instruction."""
mask_begin = ""
mask_end = ""
if ref.mask:
mask_begin = "("
mask_end = " & {:x})".format(ref.mask)
return "({} {} {} {}{:x}{} {})".format(
_TARGET_NAME[ref.target_type],
_OPERAND_NAME[ref.operand_type],
_LOCATION_NAME[ref.location],
mask_begin,
ref.ea,
mask_end,
ref.HasField('name') and ref.name or "")
def recover_instruction_references(I, inst, addr, refs):
"""Add the memory/code reference information from this instruction
into the CFG format. The LLVM side of things needs to be able to
match instruction operands to references to internal/external
code/data.
The `get_instruction_references` gives us an accurate picture of the
references as they are, but in practice we want a higher-level perspective
that resolves things like thunks to their true external representations.
Note: References are a kind of gotcha that need special explaining. We kind
of 'devirtualize' references. An example of this is:
extern:00000000002010A8 extrn stderr@@GLIBC_2_2_5
extern:00000000002010D8 ; struct _IO_FILE *stderr
extern:00000000002010D8 extrn stderr
| ; DATA XREF: .got:stderr_ptr
`-------------------------------.
|
.got:0000000000200FF0 stderr_ptr dq offset stderr
| ; DATA XREF: main+12
`-------------------------------.
|
.text:0000000000000932 mov rax, cs:stderr_ptr
.text:0000000000000939 mov rdi, [rax] ; stream
...
.text:0000000000000949 call _fprintf
So above we see that the `mov` instruction is dereferencing `stderr_ptr`,
and from there it's getting the address of `stderr`. Then it dereferences
that, which is the value of `stderr, getting us the address of the `FILE *`.
That is passed at the first argument to `fprintf`.
Now, what we see in the `mcseam-disass` log is a bit different.
Variable at 200ff0 is the external stderr
Variable at 2010a8 is the external stderr
Variable at 2010d8 is the external stderr
...
I: 932 (data mem external 200ff0 stderr)
So even though the `mov` instruction uses `stderr_ptr` and an extra level
of indirection, we devirtualize that to `stderr`. But, how could this work?
It seems like it's removing a layer of indirection. The answer is on the
LLVM side of things.
On the LLVM side, `stderr` is a global variable:
@stderr = external global %struct._IO_FILE*, align 8
And the corresponding call is:
%4 = load %struct._IO_FILE*, %struct._IO_FILE** @stderr, align 8
%5 = call i32 (...) @fprintf(%struct._IO_FILE* %4, i8* ...)
So now we see that by declaring the global variable `stderr` on the LLVM
side, we regain this extra level of indirection because all global variables
are really pointers to their type (i.e. `%struct._IO_FILE**`), thus we
preserve the intent of the original assembly.
"""
DEBUG_PUSH()
debug_info = ["I: {:x}".format(addr)]
for ref in refs:
if not ref.is_valid():
DEBUG("POSSIBLE ERROR: Invalid reference {} at instruction {:x}".format(
str(ref), inst.ea))
continue
# Redirect the thunk target to the internal target.
if ref.ea in INTERNAL_THUNK_EAS:
ref.ea = INTERNAL_THUNK_EAS[ref.ea]
ref.symbol = get_symbol_name(ref.ea)
if Reference.CODE == ref.type:
is_thunk, thunk_target_ea, thunk_name = try_get_thunk_name(ref.ea)
if is_thunk:
ref.ea = thunk_target_ea
ref.symbol = thunk_name
target_type = reference_target_type(ref)
location = reference_location(ref)
addrs = set()
R = I.xrefs.add()
R.ea = ref.ea
if ref.mask:
R.mask = ref.mask
R.operand_type = reference_operand_type(ref)
R.target_type = target_type
R.location = location
name = referenced_name(ref)
if name:
R.name = name.format('utf-8')
debug_info.append(format_instruction_reference(R))
DEBUG_POP()
DEBUG(" ".join(debug_info))
def recover_instruction_offset_table(I, table):
"""Recovers an offset table as a kind of reference."""
DEBUG("Offset-based jump table")
R = I.xrefs.add()
R.ea = table.offset
R.operand_type = CFG_pb2.CodeReference.OffsetTable
R.target_type = CFG_pb2.CodeReference.DataTarget
R.location = CFG_pb2.CodeReference.Internal
name = get_symbol_name(table.offset * table.offset_mult, allow_dummy=False)
if name:
R.name = name.format('utf-8')
def try_recovery_external_flow(I, inst, refs):
"""We have somehting like:
jmp cs:EnterCriticalSection
Where `EnterCriticalSection` is in the `.idata` section and is filled in at
load time to contain the real address of the external
`EnterCriticalSection`."""
if not (is_indirect_jump(inst) or is_indirect_function_call(inst)) or \
not refs or len(refs) > 1:
return
ref = refs[0]
if ref.type == Reference.CODE or ref.ea not in EXTERNAL_FUNCS_TO_RECOVER:
return
R = I.xrefs.add()
R.ea = ref.ea
R.name = EXTERNAL_FUNCS_TO_RECOVER[ref.ea].format('utf-8')
R.operand_type = CFG_pb2.CodeReference.ControlFlowOperand
R.target_type = CFG_pb2.CodeReference.CodeTarget
R.location = CFG_pb2.CodeReference.External
if is_indirect_jump(inst):
DEBUG("Tail-calls external {}".format(R.name))
else:
DEBUG("Calls external {}".format(R.name))
def recover_instruction(M, B, ea):
"""Recover an instruction, adding it to its parent block in the CFG."""
inst, inst_bytes = decode_instruction(ea)
I = B.instructions.add()
I.ea = ea # May not be `inst.ea` because of prefix coalescing.
I.bytes = inst_bytes
refs = get_instruction_references(inst, PIE_MODE)
recover_instruction_references(I, inst, ea, refs)
if is_noreturn_inst(inst):
I.local_noreturn = True
DEBUG_PUSH()
table = get_jump_table(inst, PIE_MODE)
if table and table.offset and \
not is_invalid_ea(table.offset * table.offset_mult):
recover_instruction_offset_table(I, table)
if not table:
try_recovery_external_flow(I, inst, refs)
DEBUG_POP()
return I
def recover_basic_block(M, F, block_ea):
"""Add in a basic block to a specific function in the CFG."""
if is_external_segment_by_flags(block_ea):
DEBUG("BB: {:x} in func {:x} is an external".format(block_ea, F.ea))
return
inst_eas, succ_eas = analyse_block(F.ea, block_ea, PIE_MODE)
DEBUG("BB: {:x} in func {:x} with {} insts".format(
block_ea, F.ea, len(inst_eas)))
B = F.blocks.add()
B.ea = block_ea
DEBUG_PUSH()
I = None
for inst_ea in inst_eas:
I = recover_instruction(M, B, inst_ea)
if I:
# Get the landing pad associated with the instructions;
# 0 if no landing pad associated
I.lp_ea = get_exception_landingpad(F, inst_ea)
DEBUG_PUSH()
if I and I.local_noreturn:
DEBUG("Does not return")
elif len(succ_eas) > 0:
B.successor_eas.extend(succ_eas)
DEBUG("Successors: {}".format(", ".join("{0:x}".format(i) for i in succ_eas)))
else:
DEBUG("No successors")
DEBUG_POP()
DEBUG_POP()
def analyze_jump_table_targets(inst, new_eas, new_func_eas):
"""Function recovery is an iterative process. Sometimes we'll find things
in the entries of the jump table that we need to go mark as code to be
added into the CFG."""
table = get_jump_table(inst, PIE_MODE)
if not table:
return
for entry_addr, entry_target in table.entries.items():
if is_start_of_function(entry_target):
DEBUG(" Jump table {:x} entry at {:x} references function at {:x}".format(
table.table_ea, entry_addr, entry_target))
new_func_eas.add(entry_target)
else:
DEBUG(" Jump table {:x} entry at {:x} references block at {:x}".format(
table.table_ea, entry_addr, entry_target))
new_eas.add(entry_target)
_RECOVERED_FUNCS = set()
def recover_function(M, func_ea, new_func_eas, entrypoints):
"""Decode a function and store it, all of its basic blocks, and all of
their instructions into the CFG file."""
global _RECOVERED_FUNCS
if func_ea in _RECOVERED_FUNCS:
return
_RECOVERED_FUNCS.add(func_ea)
if not is_start_of_function(func_ea):
DEBUG("{:x} is not a function! Not recovering.".format(func_ea))
return
F = M.funcs.add()
F.ea = func_ea
F.is_entrypoint = (func_ea in entrypoints)
name = get_symbol_name(func_ea)
if name:
DEBUG("Recovering {} at {:x}".format(name, func_ea))
F.name = name.format('utf-8')
else:
DEBUG("Recovering {:x}".format(func_ea))
DEBUG_PUSH()
# Update the protobuf with the recovered eh_frame entries
recover_exception_entries(F, func_ea)
blockset, term_insts = analyse_subroutine(func_ea, PIE_MODE)
for term_inst in term_insts:
if get_jump_table(term_inst, PIE_MODE):
DEBUG("Terminator inst {:x} in func {:x} is a jump table".format(
term_inst.ea, func_ea))
analyze_jump_table_targets(term_inst, blockset, new_func_eas)
processed_blocks = set()
while len(blockset) > 0:
block_ea = blockset.pop()
if block_ea in processed_blocks:
DEBUG("ERROR: Attempting to add same block twice: {0:x}".format(block_ea))
continue
processed_blocks.add(block_ea)
recover_basic_block(M, F, block_ea)
if TO_RECOVER["stack_var"]:
recover_variables(F, func_ea, processed_blocks)
DEBUG_POP()
def find_default_function_heads():
"""Loop through every function, to discover the heads of all blocks that
IDA recognizes. This will populate some global sets in `flow.py` that
will help distinguish block heads."""
func_heads = set()
for seg_ea in idautils.Segments():
seg_type = idc.GetSegmentAttr(seg_ea, idc.SEGATTR_TYPE)
if seg_type != idc.SEG_CODE:
continue
for func_ea in idautils.Functions(seg_ea, idc.SegEnd(seg_ea)):
if is_code_by_flags(func_ea):
func_heads.add(func_ea)
return func_heads
def recover_region_variables(M, S, seg_ea, seg_end_ea, exported_vars):
"""Look for named locations pointing into the data of this segment, and
add them to the protobuf."""
is_code_seg = is_code(seg_ea)
for ea, name in idautils.Names():
if ea < seg_ea or ea >= seg_end_ea:
continue
if is_external_segment_by_flags(ea) or ea in EXTERNAL_VARS_TO_RECOVER:
continue
if is_code_seg and is_code_by_flags(ea):
continue
# Only add named internal variables if they are referenced or exported.
if is_referenced(ea) or ea in exported_vars:
DEBUG("Variable {} at {:x}".format(name, ea))
V = S.vars.add()
V.ea = ea
V.name = name.format('utf-8')
def recover_region_cross_references(M, S, seg_ea, seg_end_ea):
"""Goes through the segment and identifies fixups that need to be
handled by the LLVM side of things."""
# Go through and look for the fixups. We start at `seg_ea - 1` because we
# always try to find the *next* fixup/heads, and if there's one right at
# the beginning of the segment then we don't want to jump to the second one.
global PIE_MODE
max_xref_width = get_address_size_in_bytes()
min_xref_width = PIE_MODE and max_xref_width or 4
is_code_seg = is_code(seg_ea)
seg_name = idc.SegName(seg_ea)
has_func_pointers = segment_contains_external_function_pointers(seg_ea)
ea, next_ea = seg_ea, seg_ea
while next_ea < seg_end_ea:
ea = next_ea
item_size = idc.ItemSize(ea)
xref_width = min(max(item_size, 4), max_xref_width)
next_ea = min(ea + xref_width,
# idc.GetNextFixupEA(ea),
idc.NextHead(ea, seg_end_ea))
# We don't want to fill the jump table bytes with their actual
# code cross-references. This is because we can't get the address
# of a basic block. Our goal is thus to preserve the original values,
# and implement the switch in terms of those original values on the
# LLVM side of things.
if is_jump_table_entry(ea):
continue
# Skip over instructions.
if is_code_seg:
flags = idc.GetFlags(ea)
if idc.isCode(flags):
next_ea = idc.NextHead(ea, seg_end_ea)
continue
target_ea = get_reference_target(ea)
# Handle entries in the `.got.plt` and `.idata` segments. In ELF binaries,
# this looks like:
#
# .got.plt:000000000032E058 off_32E058 dq offset getenv
#
# In PE binaries, this looks like:
#
# .idata:00000001400110D8 ; DWORD __stdcall GetLastError()
# .idata:00000001400110D8 extrn GetLastError:qword
if is_invalid_ea(target_ea):
if has_func_pointers and ea in EXTERNAL_FUNCS_TO_RECOVER:
target_ea = ea
# Note: it's possible that `ea == target_ea`. This happens with
# external references to things like `stderr`, where there's
# an internal slot, whose value is filled in at runtime.
if is_invalid_ea(target_ea):
continue
elif (ea % 4) != 0:
DEBUG("WARNING: Unaligned reference at {:x} to {:x}".format(ea, target_ea))
continue
elif item_size < min_xref_width:
DEBUG("WARNING: Ingorning {}-byte item that looks like at reference from {:x} to {:x}; it needs to be at least {} bytes".format(
item_size, ea, target_ea, min_xref_width))
continue
# Probably some really small number.
elif not idc.GetFlags(target_ea):
DEBUG("WARNING: No information about target {:x} from {:x}".format(
target_ea, ea))
continue
else:
X = S.xrefs.add()
X.ea = ea
X.width = xref_width
X.target_ea = target_ea
X.target_name = get_symbol_name(target_ea)
X.target_is_code = is_code(target_ea) or \
target_ea in EXTERNAL_FUNCS_TO_RECOVER
if is_external_segment(X.target_ea):
X.target_name = get_true_external_name(X.target_name)
# A cross-reference to some TLS data. Because each thread has its own
# instance of the data, this reference ends up actually being an offset
# from a thread base pointer. In x86, this tends to be the base of one of
# the segment registers, e.g. `fs` or `gs`. On the McSema side, we fill in
# this xref lazily by computing the offset.
if is_tls(target_ea):
X.target_fixup_kind = CFG_pb2.DataReference.OffsetFromThreadBase
DEBUG("{}-byte TLS offset at {:x} to {:x} ({})".format(
X.width, ea, target_ea, X.target_name))
# A cross-reference to a 'single' thing, where the fixup that we create
# will be an absolute address to the targeted variable/function.
else:
X.target_fixup_kind = CFG_pb2.DataReference.Absolute
DEBUG("{}-byte reference at {:x} to {:x} ({})".format(
X.width, ea, target_ea, X.target_name))
def recover_region(M, region_name, region_ea, region_end_ea, exported_vars):
"""Recover the data and cross-references from a segment. The data of a
segment is stored verbatim within the protobuf, and accompanied by a
series of variable and cross-reference entries."""
seg_name = idc.SegName(region_ea)
DEBUG("Recovering region {} [{:x}, {:x}) in segment {}".format(
region_name, region_ea, region_end_ea, seg_name))
seg = idaapi.getseg(region_ea)
# An item spans two regions. This may mean that there's a reference into
# the middle of an item. This happens with strings.
item_size = idc.ItemSize(region_end_ea - 1)
if 1 < item_size:
DEBUG(" ERROR: Segment should probably include {} more bytes".format(
item_size - 1))
S = M.segments.add()
S.ea = region_ea
S.data = read_bytes_slowly(region_ea, region_end_ea)
S.read_only = (seg.perm & idaapi.SEGPERM_WRITE) == 0
S.is_external = is_external_segment_by_flags(region_ea)
S.is_thread_local = is_tls_segment(region_ea)
S.name = seg_name.format('utf-8')
S.is_exported = region_ea in exported_vars
if region_name != seg_name:
S.variable_name = region_name.format('utf-8')