def exploit_constraints_call(r, ctx):
addr = r.state.stack[-2]
if not concrete(addr):
addr = z3.simplify(addr)
amount = r.state.stack[-3]
if not concrete(amount):
amount = z3.simplify(amount)
extra_constraints = []
if not concrete(addr):
extra_constraints.append(z3.Extract(159, 0, addr) == ctx.target_addr)
else:
if addr != ctx.target_addr:
raise InfeasibleExploit
if not concrete(amount):
if ctx.amount_check == '+':
extra_constraints.append(z3.UGE(amount, ctx.target_amount))
elif ctx.amount_check == '-':
extra_constraints.append(z3.UGT(amount, 0))
extra_constraints.append(z3.ULE(amount, ctx.target_amount))
else:
extra_constraints.append(amount == ctx.target_amount)
final_balance = r.state.balance
extra_constraints.append(z3.ULE(amount, final_balance))
# ensure we're not spending more for this exploit than we gain
total_spent = None
for res in r.results:
callvalue = z3.BitVec('CALLVALUE_%d' % res.xid, 256)
extra_constraints.append(z3.ULE(
callvalue,
10 * (10**18))) # keep it semi-reasonable: at most 10 Eth per call
if total_spent is None:
total_spent = callvalue
else:
total_spent += callvalue
extra_constraints.append(z3.ULT(total_spent, amount))
# also, ensure the contract does not require a unreasonable start-balance (>100 Eth)
if not ctx.initial_balance:
start_balance = z3.BitVec('BALANCE_%d' % r.results[0].xid, 256)
extra_constraints.append(z3.ULE(start_balance, 100 * (10**18)))
return extra_constraints
def run_symbolic(program,
path,
code=None,
state=None,
ctx=None,
inclusive=False):
MAX_CALLDATA_SIZE = 256
xid = gen_exec_id()
state = state or SymbolicEVMState(xid=xid, code=code)
storage = state.storage
constraints = []
sha_constraints = dict()
ctx = ctx or dict()
min_timestamp = (datetime.datetime.now() -
datetime.datetime(1970, 1, 1)).total_seconds()
# make sure we can exploit it in the foreseable future
max_timestamp = (datetime.datetime(2020, 1, 1) -
datetime.datetime(1970, 1, 1)).total_seconds()
ctx['CODESIZE-ADDRESS'] = len(code)
calldata = z3.Array('CALLDATA_%d' % xid, z3.BitVecSort(256),
z3.BitVecSort(8))
calldatasize = z3.BitVec('CALLDATASIZE_%d' % xid, 256)
instruction_count = 0
state.balance += ctx_or_symbolic('CALLVALUE', ctx, xid)
target_op = program[path[-1]].name
while state.pc in program:
state.trace.append(state.pc)
instruction_count += 1
# have we reached the end of our path?
if ((inclusive and len(path) == 0)
or (not inclusive and path == [state.pc])):
state.success = True
return SymbolicResult(xid, state, constraints, sha_constraints,
target_op)
# if not, have we reached another step of our path?
elif state.pc == path[0]:
path = path[1:]
ins = program[state.pc]
opcode = ins.op
op = ins.name
stk = state.stack
mem = state.memory
state.gas -= ins.gas
# Valid operations
# Pushes first because they are very frequent
if 0x60 <= opcode <= 0x7f:
stk.append(int.from_bytes(ins.arg, byteorder='big'))
state.pc += opcode - 0x5f # Move 1 byte forward for 0x60, up to 32 bytes for 0x7f
# Arithmetic
elif opcode < 0x10:
if op == 'STOP':
if path:
raise IntractablePath()
state.success = True
return SymbolicResult(xid, state, constraints, sha_constraints)
elif op == 'ADD':
stk.append(stk.pop() + stk.pop())
elif op == 'SUB':
stk.append(stk.pop() - stk.pop())
elif op == 'MUL':
stk.append(stk.pop() * stk.pop())
elif op == 'DIV':
s0, s1 = stk.pop(), stk.pop()
if concrete(s1):
stk.append(0 if s1 == 0 else s0 /
s1 if concrete(s0) else z3.UDiv(s0, s1))
else:
stk.append(
z3.If(s1 == 0, z3.BitVecVal(0, 256), z3.UDiv(s0, s1)))
elif op == 'MOD':
s0, s1 = stk.pop(), stk.pop()
if concrete(s1):
stk.append(0 if s1 == 0 else s0 % s1)
else:
stk.append(
z3.If(s1 == 0, z3.BitVecVal(0, 256), z3.URem(s0, s1)))
elif op == 'SDIV':
s0, s1 = stk.pop(), stk.pop()
if concrete(s0) and concrete(s1):
s0, s1 = teether.util.utils.to_signed(
s0), teether.util.utils.to_signed(s1)
stk.append(0 if s1 == 0 else abs(s0) // abs(s1) *
(-1 if s0 * s1 < 0 else 1))
elif concrete(s1):
stk.append(0 if s1 == 0 else s0 / s1)
else:
stk.append(z3.If(s1 == 0, z3.BitVecVal(0, 256), s0 / s1))
elif op == 'SMOD':
s0, s1 = stk.pop(), stk.pop()
if concrete(s0) and concrete(s1):
s0, s1 = teether.util.utils.to_signed(
s0), teether.util.utils.to_signed(s1)
stk.append(0 if s1 == 0 else abs(s0) % abs(s1) *
(-1 if s0 < 0 else 1))
elif concrete(s1):
stk.append(0 if s1 == 0 else z3.SRem(s0, s1))
else:
stk.append(
z3.If(s1 == 0, z3.BitVecVal(0, 256), z3.SRem(s0, s1)))
elif op == 'ADDMOD':
s0, s1, s2 = stk.pop(), stk.pop(), stk.pop()
if concrete(s2):
stk.append((s0 + s1) % s2 if s2 else 0)
else:
stk.append(
z3.If(s2 == 0, z3.BitVecVal(0, 256),
z3.URem((s0 + s1), s2)))
elif op == 'MULMOD':
s0, s1, s2 = stk.pop(), stk.pop(), stk.pop()
if concrete(s2):
stk.append((s0 * s1) % s2 if s2 else 0)
else:
stk.append(
z3.If(s2 == 0, z3.BitVecVal(0, 256),
z3.URem((s0 * s1), s2)))
elif op == 'EXP':
base, exponent = stk.pop(), stk.pop()
if concrete(base) and concrete(exponent):
stk.append(pow(base, exponent, teether.util.utils.TT256))
else:
if concrete(base) and teether.util.utils.is_pow2(base):
l2 = teether.util.utils.log2(base)
stk.append(1 << (l2 * exponent))
else:
raise SymbolicError(
'exponentiation with symbolic exponent currently not supported :-/'
)
elif op == 'SIGNEXTEND':
s0, s1 = stk.pop(), stk.pop()
if concrete(s0) and concrete(s1):
if s0 <= 31:
testbit = s0 * 8 + 7
if s1 & (1 << testbit):
stk.append(s1 | (teether.util.utils.TT256 -
(1 << testbit)))
else:
stk.append(s1 & ((1 << testbit) - 1))
else:
stk.append(s1)
elif concrete(s0):
if s0 <= 31:
oldwidth = (s0 + 1) * 8
stk.append(z3.SignExt(256 - oldwidth, s1))
else:
stk.append(s1)
else:
raise SymbolicError(
'symbolic bitwidth for signextension is currently not supported'
)
# Comparisons
elif opcode < 0x20:
if op == 'LT':
s0, s1 = stk.pop(), stk.pop()
if concrete(s0) and concrete(s1):
stk.append(1 if s0 < s1 else 0)
else:
stk.append(
z3.If(z3.ULT(s0, s1), z3.BitVecVal(1, 256),
z3.BitVecVal(0, 256)))
elif op == 'GT':
s0, s1 = stk.pop(), stk.pop()
if concrete(s0) and concrete(s1):
stk.append(1 if s0 > s1 else 0)
else:
stk.append(
z3.If(z3.UGT(s0, s1), z3.BitVecVal(1, 256),
z3.BitVecVal(0, 256)))
elif op == 'SLT':
s0, s1 = stk.pop(), stk.pop()
if concrete(s0) and concrete(s1):
s0, s1 = teether.util.utils.to_signed(
s0), teether.util.utils.to_signed(s1)
stk.append(1 if s0 < s1 else 0)
else:
stk.append(
z3.If(s0 < s1, z3.BitVecVal(1, 256),
z3.BitVecVal(0, 256)))
elif op == 'SGT':
s0, s1 = stk.pop(), stk.pop()
if concrete(s0) and concrete(s1):
s0, s1 = teether.util.utils.to_signed(
s0), teether.util.utils.to_signed(s1)
stk.append(1 if s0 > s1 else 0)
else:
stk.append(
z3.If(s0 > s1, z3.BitVecVal(1, 256),
z3.BitVecVal(0, 256)))
elif op == 'EQ':
s0, s1 = stk.pop(), stk.pop()
if concrete(s0) and concrete(s1):
stk.append(1 if s0 == s1 else 0)
else:
stk.append(
z3.If(s0 == s1, z3.BitVecVal(1, 256),
z3.BitVecVal(0, 256)))
elif op == 'ISZERO':
s0 = stk.pop()
if concrete(s0):
stk.append(1 if s0 == 0 else 0)
else:
stk.append(
z3.If(s0 == 0, z3.BitVecVal(1, 256),
z3.BitVecVal(0, 256)))
elif op == 'AND':
stk.append(stk.pop() & stk.pop())
elif op == 'OR':
stk.append(stk.pop() | stk.pop())
elif op == 'XOR':
stk.append(stk.pop() ^ stk.pop())
elif op == 'NOT':
stk.append(~stk.pop())
elif op == 'BYTE':
s0, s1 = stk.pop(), stk.pop()
if concrete(s0):
if s0 >= 32:
stk.append(0)
else:
if concrete(s1):
stk.append((s1 // 256**(31 - s0)) % 256)
else:
v = z3.simplify(
z3.Extract((31 - s0) * 8 + 7, (31 - s0) * 8,
s1))
if z3.is_bv_value(v):
stk.append(v.as_long())
else:
stk.append(z3.ZeroExt(256 - 32, v))
else:
raise SymbolicError('symbolic byte-index not supported')
# SHA3 and environment info
elif opcode < 0x40:
if op == 'SHA3':
s0, s1 = stk.pop(), stk.pop()
mem.extend(s0, s1)
mm = mem.read(s0, s1)
if not isinstance(mm, SymRead) and all(
concrete(m) for m in mm):
data = teether.util.utils.bytearray_to_bytestr(mm)
stk.append(
teether.util.utils.big_endian_to_int(
teether.util.utils.sha3(data)))
else:
if not isinstance(mm, SymRead):
sha_data = z3.simplify(
z3.Concat([
m if z3.is_expr(m) else z3.BitVecVal(m, 8)
for m in mm
]))
for k, v in sha_constraints.items():
if isinstance(v, SymRead):
continue
if v.size() == sha_data.size() and is_true(
v == sha_data):
sha = k
break
else:
sha = z3.BitVec(
'SHA3_%x_%d' % (instruction_count, xid), 256)
sha_constraints[sha] = sha_data
else:
sha_data = mm
sha = z3.BitVec(
'SHA3_%x_%d' % (instruction_count, xid), 256)
sha_constraints[sha] = sha_data
stk.append(sha)
# raise SymbolicError('symbolic computation of SHA3 not supported')
elif op == 'ADDRESS':
stk.append(ctx_or_symbolic('ADDRESS', ctx, xid))
elif op == 'BALANCE':
s0 = stk.pop()
if concrete(s0):
stk.append(ctx_or_symbolic('BALANCE-%x' % s0, ctx, xid))
elif is_true(
addr(s0) == addr(ctx_or_symbolic('ADDRESS', ctx,
xid))):
stk.append(state.balance)
elif is_true(
addr(s0) == addr(ctx_or_symbolic('CALLER', ctx, xid))):
stk.append(ctx_or_symbolic('BALANCE-CALLER', ctx, xid))
else:
raise SymbolicError('balance of symbolic address (%s)' %
str(z3.simplify(s0)))
elif op == 'ORIGIN':
stk.append(ctx_or_symbolic('ORIGIN', ctx, xid))
elif op == 'CALLER':
stk.append(ctx_or_symbolic('CALLER', ctx, xid))
elif op == 'CALLVALUE':
stk.append(ctx_or_symbolic('CALLVALUE', ctx, xid))
elif op == 'CALLDATALOAD':
s0 = stk.pop()
constraints.append(z3.UGE(calldatasize, s0 + 32))
if not concrete(s0):
constraints.append(z3.ULT(s0, MAX_CALLDATA_SIZE))
stk.append(z3.Concat([calldata[s0 + i] for i in range(32)]))
elif op == 'CALLDATASIZE':
stk.append(calldatasize)
elif op == 'CALLDATACOPY':
mstart, dstart, size = stk.pop(), stk.pop(), stk.pop()
constraints.append(z3.UGE(calldatasize, dstart + size))
if not concrete(dstart):
constraints.append(z3.ULT(dstart, MAX_CALLDATA_SIZE))
if concrete(size):
for i in range(size):
mem[mstart + i] = calldata[dstart + i]
else:
constraints.append(z3.ULT(size, MAX_CALLDATA_SIZE))
for i in range(MAX_CALLDATA_SIZE):
mem[mstart + i] = z3.If(size < i, mem[mstart + i],
calldata[dstart + i])
elif op == 'CODESIZE':
stk.append(len(state.code))
elif op == 'CODECOPY':
mstart, dstart, size = stk.pop(), stk.pop(), stk.pop()
if concrete(mstart) and concrete(dstart) and concrete(size):
mem.extend(mstart, size)
for i in range(size):
if dstart + i < len(state.code):
mem[mstart + i] = state.code[dstart + i]
else:
mem[mstart + i] = 0
else:
raise SymbolicError('Symbolic code index @ %s' % ins)
elif op == 'RETURNDATACOPY':
raise ExternalData('RETURNDATACOPY')
elif op == 'RETURNDATASIZE':
raise ExternalData('RETURNDATASIZE')
elif op == 'GASPRICE':
stk.append(ctx_or_symbolic('GASPRICE', ctx, xid))
elif op == 'EXTCODESIZE':
s0 = stk.pop()
if concrete(s0):
stk.append(ctx_or_symbolic('CODESIZE-%x' % s0, ctx, xid))
elif is_true(s0 == addr(ctx_or_symbolic('ADDRESS', ctx, xid))):
stk.append(ctx_or_symbolic('CODESIZE-ADDRESS', ctx, xid))
elif is_true(s0 == addr(ctx_or_symbolic('CALLER', ctx, xid))):
stk.append(ctx_or_symbolic('CODESIZE-CALLER', ctx, xid))
else:
raise SymbolicError('codesize of symblic address')
elif op == 'EXTCODECOPY':
raise ExternalData('EXTCODECOPY')
# Block info
elif opcode < 0x50:
if op == 'BLOCKHASH':
s0 = stk.pop()
if not concrete(s0):
raise SymbolicError('symbolic blockhash index')
stk.append(ctx_or_symbolic('BLOCKHASH[%d]' % s0, xid))
elif op == 'COINBASE':
stk.append(ctx_or_symbolic('COINBASE', ctx, xid))
elif op == 'TIMESTAMP':
ts = ctx_or_symbolic('TIMESTAMP', ctx, xid)
if not concrete(ts):
constraints.append(z3.UGE(ts, min_timestamp))
constraints.append(z3.ULE(ts, max_timestamp))
stk.append(ts)
elif op == 'NUMBER':
stk.append(ctx_or_symbolic('NUMBER', ctx, xid))
elif op == 'DIFFICULTY':
stk.append(ctx_or_symbolic('DIFFICULTY', ctx, xid))
elif op == 'GASLIMIT':
stk.append(ctx_or_symbolic('GASLIMIT', ctx, xid))
# VM state manipulations
elif opcode < 0x60:
if op == 'POP':
stk.pop()
elif op == 'MLOAD':
s0 = stk.pop()
mem.extend(s0, 32)
mm = [mem[s0 + i] for i in range(32)]
if all(concrete(m) for m in mm):
stk.append(
teether.util.utils.bytes_to_int(mem.read(s0, 32)))
else:
v = z3.simplify(
z3.Concat([
m if not concrete(m) else z3.BitVecVal(m, 8)
for m in mm
]))
if z3.is_bv_value(v):
stk.append(v.as_long())
else:
stk.append(v)
elif op == 'MSTORE':
s0, s1 = stk.pop(), stk.pop()
mem.extend(s0, 32)
if concrete(s1):
mem.write(s0, 32, teether.util.utils.encode_int32(s1))
else:
for i in range(32):
m = z3.simplify(
z3.Extract((31 - i) * 8 + 7, (31 - i) * 8, s1))
if z3.is_bv_value(m):
mem[s0 + i] = m.as_long()
else:
mem[s0 + i] = m
elif op == 'MSTORE8':
s0, s1 = stk.pop(), stk.pop()
mem.extend(s0, 1)
mem[s0] = s1 % 256
elif op == 'SLOAD':
s0 = stk.pop()
v = z3.simplify(storage[s0])
if z3.is_bv_value(v):
stk.append(v.as_long())
else:
stk.append(v)
elif op == 'SSTORE':
s0, s1 = stk.pop(), stk.pop()
storage[s0] = s1
elif op == 'JUMP':
s0 = stk.pop()
if not concrete(s0):
raise SymbolicError('Symbolic jump target')
state.pc = s0
if state.pc >= len(state.code) or not program[
state.pc].name == 'JUMPDEST':
raise VMException('BAD JUMPDEST')
continue
elif op == 'JUMPI':
s0, s1 = stk.pop(), stk.pop()
next_target = path[0]
if concrete(s1):
if s1:
if not concrete(s0):
raise SymbolicError('Symbolic jump target')
if s0 != next_target and state.pc + 1 == next_target:
raise IntractablePath(state.trace, path)
state.pc = s0
if state.pc >= len(state.code) or not program[
state.pc].name == 'JUMPDEST':
raise VMException('BAD JUMPDEST')
continue
else:
if concrete(s0):
if state.pc + 1 != next_target and s0 == next_target:
raise IntractablePath(state.trace, path)
else:
if state.pc + 1 == next_target:
if not (concrete(s0) and s0 == next_target):
constraints.append(s1 == 0)
elif concrete(s0) and s0 == next_target:
if state.pc + 1 != next_target:
constraints.append(s1 != 0)
state.pc = s0
if state.pc >= len(state.code) or not program[
state.pc].name == 'JUMPDEST':
raise VMException('BAD JUMPDEST')
continue
elif not concrete(s0):
raise SymbolicError('Symbolic jump target')
else:
raise IntractablePath(state.trace, path)
elif op == 'PC':
stk.append(state.pc)
elif op == 'MSIZE':
stk.append(len(mem))
elif op == 'GAS':
stk.append(z3.BitVec('GAS_%x' % instruction_count, 256))
# DUPn (eg. DUP1: a b c -> a b c c, DUP3: a b c -> a b c a)
elif op[:3] == 'DUP':
stk.append(
stk[0x7f - opcode]
) # 0x7f - opcode is a negative number, -1 for 0x80 ... -16 for 0x8f
# SWAPn (eg. SWAP1: a b c d -> a b d c, SWAP3: a b c d -> d b c a)
elif op[:4] == 'SWAP':
# 0x8e - opcode is a negative number, -2 for 0x90 ... -17 for 0x9f
stk[-1], stk[0x8e - opcode] = stk[0x8e - opcode], stk[-1]
# Logs (aka "events")
elif op[:3] == 'LOG':
"""
0xa0 ... 0xa4, 32/64/96/128/160 + len(data) gas
a. Opcodes LOG0...LOG4 are added, takes 2-6 stack arguments
MEMSTART MEMSZ (TOPIC1) (TOPIC2) (TOPIC3) (TOPIC4)
b. Logs are kept track of during tx execution exactly the same way as selfdestructs
(except as an ordered list, not a set).
Each log is in the form [address, [topic1, ... ], data] where:
* address is what the ADDRESS opcode would output
* data is mem[MEMSTART: MEMSTART + MEMSZ]
* topics are as provided by the opcode
c. The ordered list of logs in the transaction are expressed as [log0, log1, ..., logN].
"""
depth = int(op[3:])
mstart, msz = stk.pop(), stk.pop()
topics = [stk.pop() for _ in range(depth)]
mem.extend(mstart, msz)
# Ignore external effects...
# Create a new contract
elif op == 'CREATE':
s0, s1, s2 = stk.pop(), stk.pop(), stk.pop()
constraints.append(z3.UGE(state.balance, s0))
state.balance -= s0
stk.append(
addr(
z3.BitVec('EXT_CREATE_%d_%d' % (instruction_count, xid),
256)))
# Calls
elif op in ('CALL', 'CALLCODE', 'DELEGATECALL', 'STATICCALL'):
if op in ('CALL', 'CALLCODE'):
s0, s1, s2, s3, s4, s5, s6 = stk.pop(), stk.pop(), stk.pop(
), stk.pop(), stk.pop(), stk.pop(), stk.pop()
if op == 'CALL':
constraints.append(z3.UGE(state.balance, s2))
state.balance -= s2
elif op == 'DELEGATECALL':
s0, s1, s3, s4, s5, s6 = stk.pop(), stk.pop(), stk.pop(
), stk.pop(), stk.pop(), stk.pop()
s2 = ctx_or_symbolic('CALLVALUE', ctx, xid)
elif op == 'STATICCALL':
s0, s1, s3, s4, s5, s6 = stk.pop(), stk.pop(), stk.pop(
), stk.pop(), stk.pop(), stk.pop()
s2 = 0
ostart = s5 if concrete(s5) else z3.simplify(s5)
olen = s6 if concrete(s6) else z3.simplify(s6)
if concrete(s1) and s1 <= 8:
if s1 == 4:
logging.info("Calling precompiled identity contract")
istart = s3 if concrete(s3) else z3.simplify(s3)
ilen = s4 if concrete(s4) else z3.simplify(s4)
mem.copy(istart, ilen, ostart, olen)
stk.append(1)
else:
raise SymbolicError(
"Precompiled contract %d not implemented" % s1)
else:
for i in range(olen):
mem[ostart + i] = z3.BitVec(
'EXT_%d_%d_%d' % (instruction_count, i, xid), 8)
logging.info("Calling contract %s (%d_%d)" %
(s1, instruction_count, xid))
stk.append(
z3.BitVec('CALLRESULT_%d_%d' % (instruction_count, xid),
256))
elif op == 'RETURN':
s0, s1 = stk.pop(), stk.pop()
if concrete(s0) and concrete(s1):
mem.extend(s0, s1)
state.success = True
if path:
raise IntractablePath(state.trace, path)
return SymbolicResult(xid, state, constraints, sha_constraints)
# Revert opcode (Metropolis)
elif op == 'REVERT':
s0, s1 = stk.pop(), stk.pop()
if not concrete(s0) or not concrete(s1):
raise SymbolicError('symbolic memory index')
mem.extend(s0, s1)
if path:
raise IntractablePath(state.trace, path)
return SymbolicResult(xid, state, constraints, sha_constraints)
# SELFDESTRUCT opcode (also called SELFDESTRUCT)
elif op == 'SELFDESTRUCT':
s0 = stk.pop()
state.success = True
if path:
raise IntractablePath(state.trace, path)
return SymbolicResult(xid, state, constraints, sha_constraints)
state.pc += 1
if path:
raise IntractablePath(state.trace, path)
state.success = True
return SymbolicResult(xid, state, constraints, sha_constraints)