Add utilities for CrossChain messaging

contracts/access/AccessControlCrossChain.sol

@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "./AccessControl.sol";
+import "../crosschain/CrossChainEnabled.sol";
+
+/**
+ * @dev An extension to {AccessControl} with support for cross-chain access management.
+ * For each role, is extension implements an equivalent "aliased" role that is used for
+ * restricting calls originating from other chains.
+ *
+ * For example, if a function `myFunction` is protected by `onlyRole(SOME_ROLE)`, and
+ * if an address `x` has role `SOME_ROLE`, it would be able to call `myFunction` directly.
+ * A wallet or contract at the same address on another chain would however not be able
+ * to call this function. In order to do so, it would require to have the role
+ * `_crossChainRoleAlias(SOME_ROLE)`.
+ *
+ * This aliasing is required to protect against multiple contracts living at the same
+ * address on different chains but controlled by conflicting entities.
+ *
+ * _Available since v4.6._
+ */
+abstract contract AccessControlCrossChain is AccessControl, CrossChainEnabled {
+    bytes32 public constant CROSSCHAIN_ALIAS = keccak256("CROSSCHAIN_ALIAS");
+
+    /**
+     * @dev See {AccessControl-_checkRole}.
+     */
+    function _checkRole(bytes32 role) internal view virtual override {
+        if (_isCrossChain()) {
+            _checkRole(_crossChainRoleAlias(role), _crossChainSender());
+        } else {
+            super._checkRole(role);
+        }
+    }
+
+    /**
+     * @dev Returns the aliased role corresponding to `role`.
+     */
+    function _crossChainRoleAlias(bytes32 role) internal pure virtual returns (bytes32) {
+        return role ^ CROSSCHAIN_ALIAS;
+    }
+}

contracts/access/README.adoc

@@ -16,6 +16,8 @@ This directory provides ways to restrict who can access the functions of a contr
 
 {{AccessControl}}
 
+{{AccessControlCrossChain}}
+
 {{IAccessControlEnumerable}}
 
 {{AccessControlEnumerable}}

contracts/crosschain/CrossChainEnabled.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+/**
+ * @dev Provides information for building cross-chain aware contracts. This
+ * abstract contract provides accessors and modifiers to control the execution
+ * flow when receiving cross-chain messages.
+ *
+ * Actual implementations of cross-chain aware contracts, which are based on
+ * this abstraction, will  have to inherit from a bridge-specific
+ * specialization. Such specializations are provided under
+ * `crosschain/<chain>/CrossChainEnabled<chain>.sol`.
+ *
+ * _Available since v4.6._
+ */
+abstract contract CrossChainEnabled {
+    error NotCrossChainCall();
+    error InvalidCrossChainSender(address actual, address expected);
+
+    /**
+     * @dev Throws if the current function call is not the result of a
+     * cross-chain execution.
+     */
+    modifier onlyCrossChain() {
+        if (!_isCrossChain()) revert NotCrossChainCall();
+        _;
+    }
+
+    /**
+     * @dev Throws if the current function call is not the result of a
+     * cross-chain execution initiated by `account`.
+     */
+    modifier onlyCrossChainSender(address expected) {
+        address actual = _crossChainSender();
+        if (expected != actual) revert InvalidCrossChainSender(actual, expected);
+        _;
+    }
+
+    /**
+     * @dev Returns whether the current function call is the result of a
+     * cross-chain message.
+     */
+    function _isCrossChain() internal view virtual returns (bool);
+
+    /**
+     * @dev Returns the address of the sender of the cross-chain message that
+     * triggered the current function call.
+     *
+     * IMPORTANT: Should revert with `NotCrossChainCall` if the current function
+     * call is not the result of a cross-chain message.
+     */
+    function _crossChainSender() internal view virtual returns (address);
+}

contracts/crosschain/README.adoc

@@ -0,0 +1,34 @@
+= Cross Chain Awareness
+
+[.readme-notice]
+NOTE: This document is better viewed at https://docs.openzeppelin.com/contracts/api/crosschain
+
+This directory provides building blocks to improve cross-chain awareness of smart contracts.
+
+- {CrossChainEnabled} is an abstraction that contains accessors and modifiers to control the execution flow when receiving cross-chain messages.
+
+== CrossChainEnabled specializations
+
+The following specializations of {CrossChainEnabled} provide implementations of the {CrossChainEnabled} abstraction for specific bridges. This can be used to complexe cross-chain aware components such as {AccessControlCrossChain}.
+
+{{CrossChainEnabledAMB}}
+
+{{CrossChainEnabledArbitrumL1}}
+
+{{CrossChainEnabledArbitrumL2}}
+
+{{CrossChainEnabledOptimism}}
+
+{{CrossChainEnabledPolygonChild}}
+
+== Libraries for cross-chain
+
+In addition to the {CrossChainEnable} abstraction, cross-chain awareness is also available through libraries. These libraries can be used to build complex designs such as contracts with the ability to interact with multiple bridges.
+
+{{LibAMB}}
+
+{{LibArbitrumL1}}
+
+{{LibArbitrumL2}}
+
+{{LibOptimism}}

contracts/crosschain/amb/CrossChainEnabledAMB.sol

@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../CrossChainEnabled.sol";
+import "./LibAMB.sol";
+
+/**
+ * @dev [AMB](https://docs.tokenbridge.net/amb-bridge/about-amb-bridge)
+ * specialization or the {CrossChainEnabled} abstraction.
+ *
+ * As of february 2020, AMB bridges are available between the following chains:
+ * - [ETH <> xDai](https://docs.tokenbridge.net/eth-xdai-amb-bridge/about-the-eth-xdai-amb)
+ * - [ETH <> qDai](https://docs.tokenbridge.net/eth-qdai-bridge/about-the-eth-qdai-amb)
+ * - [ETH <> ETC](https://docs.tokenbridge.net/eth-etc-amb-bridge/about-the-eth-etc-amb)
+ * - [ETH <> BSC](https://docs.tokenbridge.net/eth-bsc-amb/about-the-eth-bsc-amb)
+ * - [ETH <> POA](https://docs.tokenbridge.net/eth-poa-amb-bridge/about-the-eth-poa-amb)
+ * - [BSC <> xDai](https://docs.tokenbridge.net/bsc-xdai-amb/about-the-bsc-xdai-amb)
+ * - [POA <> xDai](https://docs.tokenbridge.net/poa-xdai-amb/about-the-poa-xdai-amb)
+ * - [Rinkeby <> xDai](https://docs.tokenbridge.net/rinkeby-xdai-amb-bridge/about-the-rinkeby-xdai-amb)
+ * - [Kovan <> Sokol](https://docs.tokenbridge.net/kovan-sokol-amb-bridge/about-the-kovan-sokol-amb)
+ *
+ * _Available since v4.6._
+ */
+contract CrossChainEnabledAMB is CrossChainEnabled {
+    /// @custom:oz-upgrades-unsafe-allow state-variable-immutable
+    address private immutable _bridge;
+
+    /// @custom:oz-upgrades-unsafe-allow constructor
+    constructor(address bridge) {
+        _bridge = bridge;
+    }
+
+    /**
+     * @dev see {CrossChainEnabled-_isCrossChain}
+     */
+    function _isCrossChain() internal view virtual override returns (bool) {
+        return LibAMB.isCrossChain(_bridge);
+    }
+
+    /**
+     * @dev see {CrossChainEnabled-_crossChainSender}
+     */
+    function _crossChainSender() internal view virtual override onlyCrossChain returns (address) {
+        return LibAMB.crossChainSender(_bridge);
+    }
+}

contracts/crosschain/amb/LibAMB.sol

@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import {IAMB as AMB_Bridge} from "../../vendor/amb/IAMB.sol";
+
+/**
+ * @dev Primitives for cross-chain aware contracts using the
+ * [AMB](https://docs.tokenbridge.net/amb-bridge/about-amb-bridge)
+ * family of bridges.
+ */
+library LibAMB {
+    /**
+     * @dev Returns whether the current function call is the result of a
+     * cross-chain message relayed by `bridge`.
+     */
+    function isCrossChain(address bridge) internal view returns (bool) {
+        return msg.sender == bridge;
+    }
+
+    /**
+     * @dev Returns the address of the sender that triggered the current
+     * cross-chain message through `bridge`.
+     *
+     * NOTE: {isCrossChain} should be checked before trying to recover the
+     * sender.
+     */
+    function crossChainSender(address bridge) internal view returns (address) {
+        return AMB_Bridge(bridge).messageSender();
+    }
+}

contracts/crosschain/arbitrum/CrossChainEnabledArbitrumL1.sol

@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../CrossChainEnabled.sol";
+import "./LibArbitrumL1.sol";
+
+/**
+ * @dev [Arbitrum](https://arbitrum.io/) specialization or the
+ * {CrossChainEnabled} abstraction the L1 side (mainnet).
+ *
+ * This version should only be deployed on L1 to process cross-chain messages
+ * originating from L2. For the other side, use {CrossChainEnabledArbitrumL2}.
+ *
+ * The inbox contract is provided and maintained by the arbitrum team. You can
+ * find the address of this contract on the rinkeby testnet in
+ * [Arbitrum's developer documentation](https://developer.offchainlabs.com/docs/public_testnet#l1).
+ *
+ * _Available since v4.6._
+ */
+abstract contract CrossChainEnabledArbitrumL1 is CrossChainEnabled {
+    /// @custom:oz-upgrades-unsafe-allow state-variable-immutable
+    address private immutable _inbox;
+
+    /// @custom:oz-upgrades-unsafe-allow constructor
+    constructor(address inbox) {
+        _inbox = inbox;
+    }
+
+    /**
+     * @dev see {CrossChainEnabled-_isCrossChain}
+     */
+    function _isCrossChain() internal view virtual override returns (bool) {
+        return LibArbitrumL1.isCrossChain(_inbox);
+    }
+
+    /**
+     * @dev see {CrossChainEnabled-_crossChainSender}
+     */
+    function _crossChainSender() internal view virtual override onlyCrossChain returns (address) {
+        return LibArbitrumL1.crossChainSender(_inbox);
+    }
+}

contracts/crosschain/arbitrum/CrossChainEnabledArbitrumL2.sol

@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../CrossChainEnabled.sol";
+import "./LibArbitrumL2.sol";
+
+/**
+ * @dev [Arbitrum](https://arbitrum.io/) specialization or the
+ * {CrossChainEnabled} abstraction the L2 side (arbitrum).
+ *
+ * This version should only be deployed on L2 to process cross-chain messages
+ * originating from L1. For the other side, use {CrossChainEnabledArbitrumL1}.
+ *
+ * Arbitrum L2 includes the `ArbSys` contract at a fixed address. Therefore,
+ * this specialization of {CrossChainEnabled} does not include a constructor.
+ *
+ * _Available since v4.6._
+ */
+abstract contract CrossChainEnabledArbitrumL2 is CrossChainEnabled {
+    /**
+     * @dev see {CrossChainEnabled-_isCrossChain}
+     */
+    function _isCrossChain() internal view virtual override returns (bool) {
+        return LibArbitrumL2.isCrossChain(LibArbitrumL2.ARBSYS);
+    }
+
+    /**
+     * @dev see {CrossChainEnabled-_crossChainSender}
+     */
+    function _crossChainSender() internal view virtual override onlyCrossChain returns (address) {
+        return LibArbitrumL2.crossChainSender(LibArbitrumL2.ARBSYS);
+    }
+}

contracts/crosschain/arbitrum/LibArbitrumL1.sol

@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import {IBridge as ArbitrumL1_Bridge} from "../../vendor/arbitrum/IBridge.sol";
+import {IInbox as ArbitrumL1_Inbox} from "../../vendor/arbitrum/IInbox.sol";
+import {IOutbox as ArbitrumL1_Outbox} from "../../vendor/arbitrum/IOutbox.sol";
+
+/**
+ * @dev Primitives for cross-chain aware contracts for
+ * [Arbitrum](https://arbitrum.io/).
+ *
+ * This version should only be used on L1 to process cross-chain messages
+ * originating from L2. For the other side, use {LibArbitrumL2}.
+ */
+library LibArbitrumL1 {
+    /**
+     * @dev Returns whether the current function call is the result of a
+     * cross-chain message relayed by the bridge attached to `inbox`.
+     */
+    function isCrossChain(address inbox) internal view returns (bool) {
+        return msg.sender == ArbitrumL1_Inbox(inbox).bridge();
+    }
+
+    /**
+     * @dev Returns the address of the sender that triggered the current
+     * cross-chain message through the bridge attached to `inbox`.
+     *
+     * NOTE: {isCrossChain} should be checked before trying to recover the
+     * sender.
+     */
+    function crossChainSender(address inbox) internal view returns (address) {
+        address sender = ArbitrumL1_Outbox(ArbitrumL1_Bridge(ArbitrumL1_Inbox(inbox).bridge()).activeOutbox())
+            .l2ToL1Sender();
+        require(sender != address(0), "LibArbitrumL1: system messages without sender");
+        return sender;
+    }
+}

contracts/crosschain/arbitrum/LibArbitrumL2.sol

@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import {IArbSys as ArbitrumL2_Bridge} from "../../vendor/arbitrum/IArbSys.sol";
+
+/**
+ * @dev Primitives for cross-chain aware contracts for
+ * [Arbitrum](https://arbitrum.io/).
+ *
+ * This version should only be used on L2 to process cross-chain messages
+ * originating from L1. For the other side, use {LibArbitrumL1}.
+ */
+library LibArbitrumL2 {
+    /**
+     * @dev Returns whether the current function call is the result of a
+     * cross-chain message relayed by `arbsys`.
+     */
+    address public constant ARBSYS = 0x0000000000000000000000000000000000000064;
+
+    function isCrossChain(address arbsys) internal view returns (bool) {
+        return ArbitrumL2_Bridge(arbsys).isTopLevelCall();
+    }
+
+    /**
+     * @dev Returns the address of the sender that triggered the current
+     * cross-chain message through `arbsys`.
+     *
+     * NOTE: {isCrossChain} should be checked before trying to recover the
+     * sender.
+     */
+    function crossChainSender(address arbsys) internal view returns (address) {
+        return
+            ArbitrumL2_Bridge(arbsys).wasMyCallersAddressAliased()
+                ? ArbitrumL2_Bridge(arbsys).myCallersAddressWithoutAliasing()
+                : msg.sender;
+    }
+}