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def prove(f):
'''取自 http://rise4fun.com/Z3Py/tutorialcontent/guide#h26'''
s = Solver()
s.add(Not(f))
if s.check() == unsat:
return True
return False
class SymbolicExecutionEngine(object):
'''符号执行引擎是处理符号执行的类。它将跟踪遇到的不同方程以及程序每个点的CPU上下文。
符号变量必须由用户找到（或使用数据污染）。这不是本类的目的。
我们很幸运，只需要处理这些操作和编码：
. mov:
. mov reg32, reg32
. mov reg32, [mem]
. mov [mem], reg32
. shr:
. shr reg32, cst
. shl:
. shl reg32, cst
. and:
. and reg32, cst
. and reg32, reg32
. xor:
. xor reg32, cst
. or:
. or reg32, reg32
. add:
. add reg32, reg32
我们也不关心：
. EFLAGS
. 分支
. 较小的寄存器（16/8位）
长话短说：它是完美的；这种环境使得玩符号执行非常容易。'''
def __init__(self, start, end):
# 这是每个时间的CPU上下文
# 寄存器的值是方程字典中的索引
self.ctx = {
'eax' : None,
'ebx' : None,
'ecx' : None,
'edx' : None,
'esi' : None,
'edi' : None,
'ebp' : None,
'esp' : None,
'eip' : None
}
# 符号执行开始的地址
self.start = start
# 符号执行停止的地址
self.end = end
# 我们的反汇编器
self.disass = Disassembler(start, end)
# 这是指令可用于保存临时值/结果的内存
self.mem = {}
# 每个方程必须有唯一ID
self.idx = 0
# 符号变量将存储在那里
self.sym_variables = []
# 每个方程将存储在这里
self.equations = {}
def _check_if_reg32(self, r):
'''XXX: 做一个装饰器？'''
return r.lower() in self.ctx
def _push_equation(self, e):
self.equations[self.idx] = e
self.idx += 1
return (self.idx - 1)
def set_reg_with_equation(self, r, e):
if self._check_if_reg32(r) == False:
return
self.ctx[r] = self._push_equation(e)
def get_reg_equation(self, r):
if self._check_if_reg32(r) == False:
return
return self.equations[self.ctx[r]]
def run(self):
'''从开始地址到结束地址运行引擎'''
for mnemonic, dst, src in self.disass.get_next_instruction():
if mnemonic == 'mov':
# mov reg32, reg32
if src in self.ctx and dst in self.ctx:
self.ctx[dst] = self.ctx[src]
# mov reg32, [mem]
elif (src.find('var_') != -1 or src.find('arg') != -1) and dst in self.ctx:
if src not in self.mem:
# 尝试读取未初始化的位置，我们得到了一个符号变量！
sym = BitVec('arg%d' % len(self.sym_variables), 32)
self.sym_variables.append(sym)
print 'Trying to read a non-initialized area, we got a new symbolic variable: %s' % sym
self.mem[src] = self._push_equation(sym)
self.ctx[dst] = self.mem[src]
# mov [mem], reg32
elif dst.find('var_') != -1 and src in self.ctx:
if dst not in self.mem:
self.mem[dst] = None
self.mem[dst] = self.ctx[src]
else:
raise Exception('This encoding of "mov" is not handled.')
elif mnemonic == 'shr':
# shr reg32, cst
if dst in self.ctx and type(src) == int:
self.set_reg_with_equation(dst, LShR(self.get_reg_equation(dst), src))
else:
raise Exception('This encoding of "shr" is not handled.')
elif mnemonic == 'shl':
# shl reg32, cst
if dst in self.ctx and type(src) == int:
self.set_reg_with_equation(dst, self.get_reg_equation(dst) << src)
else:
raise Exception('This encoding of "shl" is not handled.')
elif mnemonic == 'and':
x = None
# and reg32, cst
if type(src) == int:
x = src
# and reg32, reg32
elif src in self.ctx:
x = self.get_reg_equation(src)
else:
raise Exception('This encoding of "and" is not handled.')
self.set_reg_with_equation(dst, self.get_reg_equation(dst) & x)
elif mnemonic == 'xor':
# xor reg32, cst
if dst in self.ctx and type(src) == int:
self.set_reg_with_equation(dst, self.get_reg_equation(dst) ^ src)
else:
raise Exception('This encoding of "xor" is not handled.')
elif mnemonic == 'or':
# or reg32, reg32
if dst in self.ctx and src in self.ctx:
self.set_reg_with_equation(dst, self.get_reg_equation(dst) | self.get_reg_equation(src))
else:
raise Exception('This encoding of "or" is not handled.')
elif mnemonic == 'add':
# add reg32, reg32
if dst in self.ctx and src in self.ctx:
self.set_reg_with_equation(dst, self.get_reg_equation(dst) + self.get_reg_equation(src))
else:
raise Exception('This encoding of "add" is not handled.')
else:
print mnemonic, dst, src
raise Exception('This instruction is not handled.')
def get_reg_equation_simplified(self, reg):
eq = self.get_reg_equation(reg)
eq = simplify(eq)
return eq
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