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@serpilliere @commial @WilliamBruneau @p-l- @w4kfu
"""Example of DynamicSymbolicExecution engine use
This example should run on the compiled ELF x86 64bits version of
"dse_crackme.c"
"""
from __future__ import print_function
#### This part is only related to the run of the sample, without DSE ####
from builtins import range
import os
import subprocess
import platform
from collections import namedtuple
from pdb import pm
from tempfile import NamedTemporaryFile
from future.utils import viewitems
from miasm.core.utils import int_to_byte
from miasm.jitter.csts import PAGE_READ, PAGE_WRITE
from miasm.analysis.sandbox import Sandbox_Linux_x86_64
from miasm.expression.expression import *
from miasm.os_dep.win_api_x86_32 import get_win_str_a
from miasm.core.locationdb import LocationDB
is_win = platform.system() == "Windows"
# File "management"
my_FILE_ptr = 0x11223344
FInfo = namedtuple("FInfo", ["path", "fdesc"])
FILE_to_info = {}
TEMP_FILE = NamedTemporaryFile(delete = False)
def xxx_fopen(jitter):
'''
#include <stdio.h>
FILE *fopen(const char *path, const char *mode);
'''
global my_FILE_ptr
ret_addr, args = jitter.func_args_systemv(['path', 'mode'])
fname = get_win_str_a(jitter, args.path)
FILE_to_info[my_FILE_ptr] = FInfo(fname, open(fname, "rb"))
my_FILE_ptr += 1
return jitter.func_ret_stdcall(ret_addr, my_FILE_ptr - 1)
def xxx_fread(jitter):
'''
#include <stdio.h>
size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);
'''
ret_addr, args = jitter.func_args_systemv(['ptr', 'size', 'nmemb', 'stream'])
info = FILE_to_info[args.stream]
data = info.fdesc.read(args.size * args.nmemb)
jitter.vm.set_mem(args.ptr, data)
return jitter.func_ret_stdcall(ret_addr, len(data))
def xxx_fclose(jitter):
'''
#include <stdio.h>
int fclose(FILE *stream);
'''
ret_addr, args = jitter.func_args_systemv(['stream'])
del FILE_to_info[args.stream]
return jitter.func_ret_stdcall(ret_addr, 0)
# Create sandbox
parser = Sandbox_Linux_x86_64.parser(description="ELF sandboxer")
parser.add_argument("filename", help="ELF Filename")
parser.add_argument("--strategy",
choices=["code-cov", "branch-cov", "path-cov"],
help="Strategy to use for solution creation",
default="code-cov")
options = parser.parse_args()
options.mimic_env = True
options.command_line = ["%s" % TEMP_FILE.name]
loc_db = LocationDB()
sb = Sandbox_Linux_x86_64(loc_db, options.filename, options, globals())
# Init segment
sb.jitter.lifter.do_stk_segm = True
sb.jitter.lifter.do_ds_segm = True
sb.jitter.lifter.do_str_segm = True
sb.jitter.lifter.do_all_segm = True
FS_0_ADDR = 0x7ff70000
sb.jitter.cpu.FS = 0x4
sb.jitter.cpu.set_segm_base(sb.jitter.cpu.FS, FS_0_ADDR)
sb.jitter.vm.add_memory_page(
FS_0_ADDR + 0x28,
PAGE_READ,
b"\x42\x42\x42\x42\x42\x42\x42\x42",
"Stack canary FS[0x28]"
)
# Prepare the execution
sb.jitter.init_run(sb.entry_point)
#### This part handle the DSE ####
from miasm.analysis.dse import DSEPathConstraint
from miasm.analysis.machine import Machine
# File "management"
class SymbolicFile(object):
"""Symbolic file with read operation, returning symbolic bytes"""
def __init__(self, fname):
self.fname = fname
self.position = 0
self.max_size = os.stat(fname).st_size
self.gen_bytes = {}
self.state = "OPEN"
def read(self, length):
assert self.state == "OPEN"
out = []
for i in range(self.position, min(self.position + length,
self.max_size)):
if i not in self.gen_bytes:
ret = ExprId("SF_%08x_%d" % (id(self), i), 8)
self.gen_bytes[i] = ret
out.append(self.gen_bytes[i])
self.position += 1
return out
def close(self):
self.state = "CLOSE"
FILE_to_info_symb = {}
FILE_stream = ExprId("FILE_0", 64)
FILE_size = ExprId("FILE_0_size", 64)
def xxx_fopen_symb(dse):
regs = dse.lifter.arch.regs
fname_addr = dse.eval_expr(regs.RDI)
mode = dse.eval_expr(regs.RSI)
assert fname_addr.is_int()
assert mode.is_int()
fname = get_win_str_a(dse.jitter, int(fname_addr))
ret_addr = ExprInt(dse.jitter.get_stack_arg(0), regs.RIP.size)
assert len(FILE_to_info_symb) == 0
ret_value = FILE_stream
FILE_to_info_symb[ret_value] = SymbolicFile(fname)
dse.update_state({
regs.RSP: dse.eval_expr(regs.RSP + ExprInt(8, regs.RSP.size)),
dse.lifter.IRDst: ret_addr,
regs.RIP: ret_addr,
regs.RAX: ret_value,
})
def xxx_fread_symb(dse):
regs = dse.lifter.arch.regs
ptr = dse.eval_expr(regs.RDI)
size = dse.eval_expr(regs.RSI)
nmemb = dse.eval_expr(regs.RDX)
stream = dse.eval_expr(regs.RCX)
assert size.is_int()
assert nmemb.is_int()
# Fill the buffer with symbolic bytes
update = {}
sf = FILE_to_info_symb[stream]
data = sf.read(int(size) * int(nmemb))
for i, content in enumerate(data):
addr = dse.symb.expr_simp(ptr + ExprInt(i, ptr.size))
update[ExprMem(addr, 8)] = content
ret_addr = ExprInt(dse.jitter.get_stack_arg(0), regs.RIP.size)
ret_value = FILE_size
update.update({
regs.RSP: dse.symb.eval_expr(regs.RSP + ExprInt(8, regs.RSP.size)),
dse.lifter.IRDst: ret_addr,
regs.RIP: ret_addr,
regs.RAX: ret_value,
})
dse.update_state(update)
def xxx_fclose_symb(dse):
regs = dse.lifter.arch.regs
stream = dse.eval_expr(regs.RDI)
FILE_to_info_symb[stream].close()
ret_addr = ExprInt(dse.jitter.get_stack_arg(0), regs.RIP.size)
dse.update_state({
regs.RSP: dse.symb.eval_expr(regs.RSP + ExprInt(8, regs.RSP.size)),
dse.lifter.IRDst: ret_addr,
regs.RIP: ret_addr,
regs.RAX: ExprInt(0, regs.RAX.size),
})
# Symbolic naive version of _libc_start_main
def xxx___libc_start_main_symb(dse):
# ['RDI', 'RSI', 'RDX', 'RCX', 'R8', 'R9']
# main, argc, argv, ...
regs = dse.lifter.arch.regs
top_stack = dse.eval_expr(regs.RSP)
main_addr = dse.eval_expr(regs.RDI)
argc = dse.eval_expr(regs.RSI)
argv = dse.eval_expr(regs.RDX)
hlt_addr = ExprInt(sb.CALL_FINISH_ADDR, 64)
dse.update_state({
ExprMem(top_stack, 64): hlt_addr,
regs.RDI: argc,
regs.RSI: argv,
dse.lifter.IRDst: main_addr,
dse.lifter.pc: main_addr,
})
# Stop the execution on puts and get back the corresponding string
class FinishOn(Exception):
def __init__(self, string):
self.string = string
super(FinishOn, self).__init__()
def xxx_puts_symb(dse):
string = get_win_str_a(dse.jitter, dse.jitter.cpu.RDI)
raise FinishOn(string)
todo = set([b""]) # Set of file content to test
# Instantiate the DSE engine
machine = Machine("x86_64")
# Convert strategy to the correct value
strategy = {
"code-cov": DSEPathConstraint.PRODUCE_SOLUTION_CODE_COV,
"branch-cov": DSEPathConstraint.PRODUCE_SOLUTION_BRANCH_COV,
"path-cov": DSEPathConstraint.PRODUCE_SOLUTION_PATH_COV,
}[options.strategy]
dse = DSEPathConstraint(machine, loc_db, produce_solution=strategy)
# Attach to the jitter
dse.attach(sb.jitter)
# Update the jitter state: df is read, but never set
# Approaches: specific or generic
# - Specific:
# df_value = ExprInt(sb.jitter.cpu.df, dse.lifter.arch.regs.df.size)
# dse.update_state({
# dse.lifter.arch.regs.df: df_value
# })
# - Generic:
dse.update_state_from_concrete()
# Add constraint on file size, we don't want to generate too big FILE
z3_file_size = dse.z3_trans.from_expr(FILE_size)
dse.cur_solver.add(0 < z3_file_size)
dse.cur_solver.add(z3_file_size < 0x10)
# Register symbolic stubs for extern functions (xxx_puts_symb, ...)
dse.add_lib_handler(sb.libs, globals())
# Automatic exploration of solution
## Save the current clean state, before any computation of the FILE content
snapshot = dse.take_snapshot()
found = False
while todo:
# Prepare a solution to try, based on the clean state
file_content = todo.pop()
print("CUR: %r" % file_content)
open(TEMP_FILE.name, "wb").write(file_content)
dse.restore_snapshot(snapshot, keep_known_solutions=True)
FILE_to_info.clear()
FILE_to_info_symb.clear()
# Play the current file
try:
sb.run()
except FinishOn as finish_info:
print(finish_info.string)
if finish_info.string == "OK":
# Stop if the expected result is found
found = True
break
finfo = FILE_to_info_symb[FILE_stream]
for sol_ident, model in viewitems(dse.new_solutions):
# Build the file corresponding to solution in 'model'
out = []
fsize = max(model.eval(dse.z3_trans.from_expr(FILE_size)).as_long(),
len(finfo.gen_bytes))
for index in range(fsize):
try:
byteid = finfo.gen_bytes[index]
out.append(int_to_byte(model.eval(dse.z3_trans.from_expr(byteid)).as_long()))
except (KeyError, AttributeError) as _:
# Default value if there is no constraint on current byte
out.append(b"\x00")
todo.add(b"".join(out))
# Assert that the result has been found
assert found == True
print("FOUND !")
TEMP_FILE.close()
# Replay for real
if not is_win:
print("Trying to launch the binary without Miasm")
crackme = subprocess.Popen([options.filename, TEMP_FILE.name],
stdout=subprocess.PIPE,
stderr=subprocess.PIPE)
stdout, stderr = crackme.communicate()
assert not stderr
os.unlink(TEMP_FILE.name)
stdout = stdout.strip()
print(stdout)
assert stdout == b"OK"
else:
os.unlink(TEMP_FILE.name)