research/impurity/check_for_impurity.se

macro calldatachar($x):
    div(calldataload($x), 2**248)

# sum([2**x for x in [0x31, 0x32, 0x33, 0x3a, 0x3b, 0x3c, 0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x54, 0x55, 0xf0, 0xff]])
mask = 57897811465722876096115075801844696845150819816717216876035649536196444422144

data approved_addrs[]

def submit(addr: address):
    # Copy external contract code
    extcode = string(~extcodesize(addr))
    ~extcodecopy(addr, extcode, 0, ~extcodesize(addr))
    ops = array(~extcodesize(addr))
    pushargs = array(~extcodesize(addr))
    # Loop through the code
    with i = 0:
        with op = 0:
            while i < len(extcode):
                with c = ~mod(~mload(extcode + i - 31), 256):
                    # Banned opcode
                    if ~and(2**c, mask):
                        ~invalid()
                    # PUSH
                    if 0x60 <= c and c <= 0x7f:
                        pushargs[op] = ~div(~mload(extcode + i + 1), 256 ** (0x7f - c))
                        i += c - 0x5e
                    # Call, callcode, delegatecall
                    elif c == 0xf1 or c == 0xf2 or c == 0xf4:
                        # Pattern-match four ways of setting the gas parameter:
                        #
                        # 1. PUSH<value>
                        # 2. sub(GAS, PUSH<value>)
                        # 3. GAS
                        # 4. SWAP1 <address> (<gas> ... )
                        # 5. DUP
                        if op >= 2 and ops[op - 1] >= 0x60 and ops[op - 1] <= 0x7f:
                            address_entry = op - 2
                        elif op >= 4 and ops[op - 1] == 0x03 and ops[op - 2] == 0x5a and ops[op - 3] >= 0x60 and ops[op - 3] <= 0x7f:
                            address_entry = op - 4
                        elif op >= 2 and ops[op - 1] == 0x5a:
                            address_entry = op - 2
                        elif op >= 2 and ops[op - 1] == 0x90:
                            address_entry = op - 2
                        elif op >= 2 and ops[op - 1] >= 0x80 and ops[op - 1] < 0x90:
                            address_entry = op - 2
                        else:
                            ~invalid()
                        # Operation before the gas parameter must satisfy one of three conditions:
                        #
                        # 1. It is a PUSH of an already approved address
                        # 2. It is the address itself, through the ADDRESS opcode (ie. self-calling is permitted)
                        # 3. It is a PUSH1, ie. less than 256 (ie. a present or future precompile)
                        if self.approved_addrs[pushargs[address_entry]]:
                            success = 1
                        elif ops[address_entry] == 0x30:
                            success = 1
                        elif ops[address_entry] == 0x60:
                            success = 1
                        if not success:
                            ~invalid()
                        i += 1
                    else:
                        i += 1
                    ops[op] = c
                    op += 1
    self.approved_addrs[addr] = 1
    return(1: bool)

def const check(addr: address):
    return(self.approved_addrs[addr]:bool)