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test_worst_bytecode_single_opcode()

Documentation for tests/zkevm/test_worst_bytecode.py::test_worst_bytecode_single_opcode@44293f1e.

Generate fixtures for these test cases for Prague with:

fill -v tests/zkevm/test_worst_bytecode.py::test_worst_bytecode_single_opcode --fork Prague

Test a block execution where a single opcode execution maxes out the gas limit, and the opcodes access a huge amount of contract code.

We first use a single block to deploy a factory contract that will be used to deploy a large number of contracts.

This is done to avoid having a big pre-allocation size for the test.

The test is performed in the last block of the test, and the entire block gas limit is consumed by repeated opcode executions.

Source code in tests/zkevm/test_worst_bytecode.py 
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@pytest.mark.parametrize(
    "opcode",
    [
        Op.EXTCODESIZE,
        Op.EXTCODEHASH,
        Op.CALL,
        Op.CALLCODE,
        Op.DELEGATECALL,
        Op.STATICCALL,
        Op.EXTCODECOPY,
    ],
)
@pytest.mark.slow()
@pytest.mark.valid_from("Cancun")
def test_worst_bytecode_single_opcode(
    blockchain_test: BlockchainTestFiller,
    pre: Alloc,
    fork: Fork,
    opcode: Op,
):
    """
    Test a block execution where a single opcode execution maxes out the gas limit,
    and the opcodes access a huge amount of contract code.

    We first use a single block to deploy a factory contract that will be used to deploy
    a large number of contracts.

    This is done to avoid having a big pre-allocation size for the test.

    The test is performed in the last block of the test, and the entire block gas limit is
    consumed by repeated opcode executions.
    """
    # We use 100G gas limit to be able to deploy a large number of contracts in a single block,
    # avoiding bloating the number of preparing blocks in the test.
    env = Environment(gas_limit=100_000_000_000)
    attack_gas_limit = Environment().gas_limit

    # The initcode will take its address as a starting point to the input to the keccak
    # hash function.
    # It will reuse the output of the hash function in a loop to create a large amount of
    # seemingly random code, until it reaches the maximum contract size.
    initcode = (
        Op.MSTORE(0, Op.ADDRESS)
        + While(
            body=(
                Op.SHA3(Op.SUB(Op.MSIZE, 32), 32)
                # Use a xor table to avoid having to call the "expensive" sha3 opcode as much
                + sum(
                    (Op.PUSH32[xor_value] + Op.XOR + Op.DUP1 + Op.MSIZE + Op.MSTORE)
                    for xor_value in XOR_TABLE
                )
                + Op.POP
            ),
            condition=Op.LT(Op.MSIZE, MAX_CONTRACT_SIZE),
        )
        # Despite the whole contract has random bytecode, we make the first opcode be a STOP
        # so CALL-like attacks return as soon as possible, while EXTCODE(HASH|SIZE) work as
        # intended.
        + Op.MSTORE8(0, 0x00)
        + Op.RETURN(0, MAX_CONTRACT_SIZE)
    )
    initcode_address = pre.deploy_contract(code=initcode)

    # The factory contract will simply use the initcode that is already deployed,
    # and create a new contract and return its address if successful.
    factory_code = (
        Op.EXTCODECOPY(
            address=initcode_address,
            dest_offset=0,
            offset=0,
            size=Op.EXTCODESIZE(initcode_address),
        )
        + Op.MSTORE(
            0,
            Op.CREATE2(
                value=0,
                offset=0,
                size=Op.EXTCODESIZE(initcode_address),
                salt=Op.SLOAD(0),
            ),
        )
        + Op.SSTORE(0, Op.ADD(Op.SLOAD(0), 1))
        + Op.RETURN(0, 32)
    )
    factory_address = pre.deploy_contract(code=factory_code)

    # The factory caller will call the factory contract N times, creating N new contracts.
    # Calldata should contain the N value.
    factory_caller_code = Op.CALLDATALOAD(0) + While(
        body=Op.POP(Op.CALL(address=factory_address)),
        condition=Op.PUSH1(1) + Op.SWAP1 + Op.SUB + Op.DUP1 + Op.ISZERO + Op.ISZERO,
    )
    factory_caller_address = pre.deploy_contract(code=factory_caller_code)

    gas_costs = fork.gas_costs()
    intrinsic_gas_cost_calc = fork.transaction_intrinsic_cost_calculator()
    loop_cost = (
        gas_costs.G_KECCAK_256  # KECCAK static cost
        + math.ceil(85 / 32) * gas_costs.G_KECCAK_256_WORD  # KECCAK dynamic cost for CREATE2
        + gas_costs.G_VERY_LOW * 3  # ~MSTOREs+ADDs
        + gas_costs.G_COLD_ACCOUNT_ACCESS  # Opcode cost
        + 30  # ~Gluing opcodes
    )
    num_contracts = (
        # Base available gas = GAS_LIMIT - intrinsic - (out of loop MSTOREs)
        attack_gas_limit - intrinsic_gas_cost_calc() - gas_costs.G_VERY_LOW * 4
    ) // loop_cost

    contracts_deployment_tx = Transaction(
        to=factory_caller_address,
        gas_limit=env.gas_limit,
        gas_price=10**9,
        data=Hash(num_contracts),
        sender=pre.fund_eoa(),
    )

    post = {}
    deployed_contract_addresses = []
    for i in range(num_contracts):
        deployed_contract_address = compute_create2_address(
            address=factory_address,
            salt=i,
            initcode=initcode,
        )
        post[deployed_contract_address] = Account(nonce=1)
        deployed_contract_addresses.append(deployed_contract_address)

    attack_call = Bytecode()
    if opcode == Op.EXTCODECOPY:
        attack_call = Op.EXTCODECOPY(address=Op.SHA3(32 - 20 - 1, 85), dest_offset=85, size=1000)
    else:
        # For the rest of the opcodes, we can use the same generic attack call
        # since all only minimally need the `address` of the target.
        attack_call = Op.POP(opcode(address=Op.SHA3(32 - 20 - 1, 85)))
    attack_code = (
        # Setup memory for later CREATE2 address generation loop.
        # 0xFF+[Address(20bytes)]+[seed(32bytes)]+[initcode keccak(32bytes)]
        Op.MSTORE(0, factory_address)
        + Op.MSTORE8(32 - 20 - 1, 0xFF)
        + Op.MSTORE(32, 0)
        + Op.MSTORE(64, initcode.keccak256())
        # Main loop
        + While(
            body=attack_call + Op.MSTORE(32, Op.ADD(Op.MLOAD(32), 1)),
        )
    )

    if len(attack_code) > MAX_CONTRACT_SIZE:
        # TODO: A workaround could be to split the opcode code into multiple contracts
        # and call them in sequence.
        raise ValueError(
            f"Code size {len(attack_code)} exceeds maximum code size {MAX_CONTRACT_SIZE}"
        )
    opcode_address = pre.deploy_contract(code=attack_code)
    opcode_tx = Transaction(
        to=opcode_address,
        gas_limit=attack_gas_limit,
        gas_price=10**9,
        sender=pre.fund_eoa(),
    )

    blockchain_test(
        genesis_environment=env,
        pre=pre,
        post=post,
        blocks=[
            Block(txs=[contracts_deployment_tx]),
            Block(txs=[opcode_tx]),
        ],
        exclude_full_post_state_in_output=True,
    )

Parametrized Test Cases

The interactive table below is also available as a standalone page.

Test ID (Abbreviated) opcode
...fork_Cancun-blockchain_test-opcode_EXTCODESIZE EXTCODESIZE
...fork_Cancun-blockchain_test-opcode_EXTCODEHASH EXTCODEHASH
...fork_Cancun-blockchain_test-opcode_CALL CALL
...fork_Cancun-blockchain_test-opcode_CALLCODE CALLCODE
...fork_Cancun-blockchain_test-opcode_DELEGATECALL DELEGATECALL
...fork_Cancun-blockchain_test-opcode_STATICCALL STATICCALL
...fork_Cancun-blockchain_test-opcode_EXTCODECOPY EXTCODECOPY
...fork_Prague-blockchain_test-opcode_EXTCODESIZE EXTCODESIZE
...fork_Prague-blockchain_test-opcode_EXTCODEHASH EXTCODEHASH
...fork_Prague-blockchain_test-opcode_CALL CALL
...fork_Prague-blockchain_test-opcode_CALLCODE CALLCODE
...fork_Prague-blockchain_test-opcode_DELEGATECALL DELEGATECALL
...fork_Prague-blockchain_test-opcode_STATICCALL STATICCALL
...fork_Prague-blockchain_test-opcode_EXTCODECOPY EXTCODECOPY
...fork_Osaka-blockchain_test-opcode_EXTCODESIZE EXTCODESIZE
...fork_Osaka-blockchain_test-opcode_EXTCODEHASH EXTCODEHASH
...fork_Osaka-blockchain_test-opcode_CALL CALL
...fork_Osaka-blockchain_test-opcode_CALLCODE CALLCODE
...fork_Osaka-blockchain_test-opcode_DELEGATECALL DELEGATECALL
...fork_Osaka-blockchain_test-opcode_STATICCALL STATICCALL
...fork_Osaka-blockchain_test-opcode_EXTCODECOPY EXTCODECOPY