feat(ctb): Enforce maximum L2 gas limit

Enforces a maximum L2 gas limit within the `SystemConfig`. This change
helps ensure that OP Stack chain governors keep the L2 block gas limit
within a reasonable range in order to guarantee that the L2 blocks may
be proven.

* In the `_setResourceConfig` function, the new minimum gas limit is
checked to be less than the current `gasLimit`. This value may never be
larger than `MAX_GAS_LIMIT`, per the checks in `_setGasLimit`. This
ensures that the `minimumGasLimit <= maximumGasLimit`

packages/contracts-bedrock/semver-lock.json

@@ -48,8 +48,8 @@
     "sourceCodeHash": "0xd6a894e371c2c7182b5960c507491f81c3775dda0efedd29475f7c30ca07b004"
   },
   "src/L1/SystemConfig.sol": {
-    "initCodeHash": "0xace1ef0e25a5416a686c7555acd20e9b0191ab2a8c8320d57606ed12092ccbb6",
-    "sourceCodeHash": "0x1f35f55aa230a686f6457e42bd08acc8bd94d691f89ac23a4b2efd7cc1eefdc6"
+    "initCodeHash": "0x2d49139c443ba0d3dfe03bbc6ba53390c4a6763be50a3ae4245d510773040214",
+    "sourceCodeHash": "0xe89e2be12f8ef3d2a8e7dda0c81d510b5b4360faa5992e945c2306418da99fa8"
   },
   "src/L2/BaseFeeVault.sol": {
     "initCodeHash": "0x2744d34573be83206d1b75d049d18a7bb37f9058e68c0803e5008c46b0dc2474",

packages/contracts-bedrock/snapshots/abi/SystemConfig.json

@@ -404,6 +404,19 @@
     "stateMutability": "view",
     "type": "function"
   },
+  {
+    "inputs": [],
+    "name": "maximumGasLimit",
+    "outputs": [
+      {
+        "internalType": "uint64",
+        "name": "",
+        "type": "uint64"
+      }
+    ],
+    "stateMutability": "pure",
+    "type": "function"
+  },
   {
     "inputs": [],
     "name": "minimumGasLimit",

packages/contracts-bedrock/src/L1/SystemConfig.sol

@@ -84,6 +84,11 @@ contract SystemConfig is OwnableUpgradeable, ISemver, IGasToken {
     /// @notice The number of decimals that the gas paying token has.
     uint8 internal constant GAS_PAYING_TOKEN_DECIMALS = 18;
 
+    /// @notice The maximum gas limit that can be set for L2 blocks. This limit is used to enforce that the blocks
+    ///         on L2 are not too large to process and prove. Over time, this value can be increased as various
+    ///         optimizations and improvements are made to the system at large.
+    uint64 internal constant MAX_GAS_LIMIT = 100_000_000;
+
     /// @notice Fixed L2 gas overhead. Used as part of the L2 fee calculation.
     uint256 public overhead;
 
@@ -110,8 +115,8 @@ contract SystemConfig is OwnableUpgradeable, ISemver, IGasToken {
     event ConfigUpdate(uint256 indexed version, UpdateType indexed updateType, bytes data);
 
     /// @notice Semantic version.
-    /// @custom:semver 2.1.0
-    string public constant version = "2.1.0";
+    /// @custom:semver 2.2.0
+    string public constant version = "2.2.0";
 
     /// @notice Constructs the SystemConfig contract. Cannot set
     ///         the owner to `address(0)` due to the Ownable contract's
@@ -208,6 +213,14 @@ contract SystemConfig is OwnableUpgradeable, ISemver, IGasToken {
         return uint64(_resourceConfig.maxResourceLimit) + uint64(_resourceConfig.systemTxMaxGas);
     }
 
+    /// @notice Returns the maximum L2 gas limit that can be safely set for the system to
+    ///         operate. This bound is used to prevent the gas limit from being set too high
+    ///         and causing the system to be unable to process and/or prove L2 blocks.
+    /// @return uint64 Maximum gas limit.
+    function maximumGasLimit() public pure returns (uint64) {
+        return MAX_GAS_LIMIT;
+    }
+
     /// @notice High level getter for the unsafe block signer address.
     ///         Unsafe blocks can be propagated across the p2p network if they are signed by the
     ///         key corresponding to this address.
@@ -360,6 +373,7 @@ contract SystemConfig is OwnableUpgradeable, ISemver, IGasToken {
     /// @param _gasLimit New gas limit.
     function _setGasLimit(uint64 _gasLimit) internal {
         require(_gasLimit >= minimumGasLimit(), "SystemConfig: gas limit too low");
+        require(_gasLimit <= maximumGasLimit(), "SystemConfig: gas limit too high");
         gasLimit = _gasLimit;
 
         bytes memory data = abi.encode(_gasLimit);

packages/contracts-bedrock/test/L1/SystemConfig.t.sol

@@ -398,6 +398,22 @@ contract SystemConfig_Setters_TestFail is SystemConfig_Init {
         systemConfig.setResourceConfig(config);
     }
 
+    /// @dev Tests that `setGasLimit` reverts if the gas limit is too low.
+    function test_setGasLimit_lowGasLimit_reverts() external {
+        uint64 minimumGasLimit = systemConfig.minimumGasLimit();
+        vm.prank(systemConfig.owner());
+        vm.expectRevert("SystemConfig: gas limit too low");
+        systemConfig.setGasLimit(minimumGasLimit - 1);
+    }
+
+    /// @dev Tests that `setGasLimit` reverts if the gas limit is too high.
+    function test_setGasLimit_highGasLimit_reverts() external {
+        uint64 maximumGasLimit = systemConfig.maximumGasLimit();
+        vm.prank(systemConfig.owner());
+        vm.expectRevert("SystemConfig: gas limit too high");
+        systemConfig.setGasLimit(maximumGasLimit + 1);
+    }
+
     /// @dev Tests that `setResourceConfig` reverts if the min base fee
     ///      is greater than the maximum allowed base fee.
     function test_setResourceConfig_badMinMax_reverts() external {

packages/contracts-bedrock/test/invariants/SystemConfig.t.sol

@@ -6,7 +6,7 @@ import { SystemConfig } from "src/L1/SystemConfig.sol";
 import { Proxy } from "src/universal/Proxy.sol";
 import { Constants } from "src/libraries/Constants.sol";
 
-contract SystemConfig_GasLimitLowerBound_Invariant is Test {
+contract SystemConfig_GasLimitBoundaries_Invariant is Test {
     SystemConfig public config;
 
     function setUp() external {
@@ -64,8 +64,11 @@ contract SystemConfig_GasLimitLowerBound_Invariant is Test {
     }
 
     /// @custom:invariant The gas limit of the `SystemConfig` contract can never be lower
-    ///                   than the hard-coded lower bound.
-    function invariant_gasLimitLowerBound() external view {
+    ///                   than the hard-coded lower bound, higher than the hard-coded upper
+    //                    bound, and that the lower bound is never higher than the upper bound.
+    function invariant_gasLimitBoundaries() external view {
         assertTrue(config.gasLimit() >= config.minimumGasLimit());
+        assertTrue(config.gasLimit() <= config.maximumGasLimit());
+        assertTrue(config.minimumGasLimit() <= config.maximumGasLimit());
     }
 }

packages/contracts-bedrock/test/kontrol/proofs/utils/DeploymentSummary.sol

@@ -30,7 +30,7 @@ contract DeploymentSummary is DeploymentSummaryCode {
     address internal constant safeSingletonAddress = 0x90193C961A926261B756D1E5bb255e67ff9498A1;
     address internal constant superchainConfigAddress = 0x068E44eB31e111028c41598E4535be7468674D0A;
     address internal constant superchainConfigProxyAddress = 0xDEb1E9a6Be7Baf84208BB6E10aC9F9bbE1D70809;
-    address internal constant systemConfigAddress = 0x809abd1c13738dE7a76C85839779FCaa59FA32CE;
+    address internal constant systemConfigAddress = 0x6B8e3fA7da8d819695ec09AD697E911401dA82b9;
     address internal constant systemConfigProxyAddress = 0x1c23A6d89F95ef3148BCDA8E242cAb145bf9c0E4;
     address internal constant systemOwnerSafeAddress = 0x7d039be7F9b5190147621b02e82B250e1D748e02;
 
@@ -281,7 +281,7 @@ contract DeploymentSummary is DeploymentSummaryCode {
         value = hex"0000000000000000000000000000000000000000000000000000000000000003";
         vm.store(systemOwnerSafeAddress, slot, value);
         slot = hex"360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc";
-        value = hex"000000000000000000000000809abd1c13738de7a76c85839779fcaa59fa32ce";
+        value = hex"0000000000000000000000006b8e3fa7da8d819695ec09ad697e911401da82b9";
         vm.store(systemConfigProxyAddress, slot, value);
         slot = hex"0000000000000000000000000000000000000000000000000000000000000000";
         value = hex"0000000000000000000000000000000000000000000000000000000000000001";