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226 | @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.
"""
# The attack gas limit is the gas limit which the target tx will use
# The test will scale the block gas limit to setup the contracts accordingly to be
# able to pay for the contract deposit. This has to take into account the 200 gas per byte,
# but also the quadratic memory expansion costs which have to be paid each time the
# memory is being setup
attack_gas_limit = Environment().gas_limit
max_contract_size = fork.max_code_size()
gas_costs = fork.gas_costs()
# Calculate the absolute minimum gas costs to deploy the contract
# This does not take into account setting up the actual memory (using KECCAK256 and XOR)
# so the actual costs of deploying the contract is higher
memory_expansion_gas_calculator = fork.memory_expansion_gas_calculator()
memory_gas_minimum = memory_expansion_gas_calculator(new_bytes=len(bytes(max_contract_size)))
code_deposit_gas_minimum = (
fork.gas_costs().G_CODE_DEPOSIT_BYTE * max_contract_size + memory_gas_minimum
)
intrinsic_gas_cost_calc = fork.transaction_intrinsic_cost_calculator()
# Calculate the loop cost of the attacker to query one address
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
)
# Calculate the number of contracts to be targeted
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
# Set the block gas limit to a relative high value to ensure the code deposit tx
# fits in the block (there is enough gas available in the block to execute this)
env = Environment(gas_limit=code_deposit_gas_minimum * 2 * num_contracts)
# 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)
contracts_deployment_tx = Transaction(
to=factory_caller_address,
gas_limit=env.gas_limit,
gas_price=10**6,
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,
)
|