llvm-context: disable call re-entrancy for send and transfer (#196)

CHANGELOG.md

@@ -15,6 +15,8 @@ Supported `polkadot-sdk` rev: `274a781e8ca1a9432c7ec87593bd93214abbff50`
 - Removed support for legacy EVM assembly (EVMLA) translation.
 - integration: identify cached code blobs on source code to fix potential confusions.
 - Setting base, include or allow paths in emscripten is now a hard error.
+- Employ a heuristic to detect `address.transfer` and `address.send` calls.
+  If detected, the re-entrant call flag is not set and 0 deposit limit is endowed.
 
 ### Fixed
 - Solidity: Add the solc `--libraries` files to sources.

crates/integration/contracts/Balance.sol

@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8;
+
+/* runner.json
+{
+    "differential": true,
+    "actions": [
+        {
+            "Upload": {
+                "code": {
+                    "Solidity": {
+                        "contract": "BalanceReceiver"
+                    }
+                }
+            }
+        },
+        {
+            "Instantiate": {
+                "code": {
+                    "Solidity": {
+                        "contract": "Balance"
+                    }
+                },
+                "value": 24
+            }
+        },
+        {
+            "Call": {
+                "dest": {
+                    "Instantiated": 0
+                },
+                "data": "1c8d16b30000000000000000000000000303030303030303030303030303030303030303000000000000000000000000000000000000000000000000000000000000000a"
+            }
+        },
+        {
+            "Call": {
+                "dest": {
+                    "Instantiated": 0
+                },
+                "data": "6ada15d90000000000000000000000000303030303030303030303030303030303030303000000000000000000000000000000000000000000000000000000000000000a"
+            }
+        }
+    ]
+}
+*/
+
+contract BalanceReceiver {
+    constructor() payable {}
+
+    fallback() external payable {}
+}
+
+contract Balance {
+    constructor() payable {
+        // 0 to EOA
+        transfer_to(payable(address(0xdeadbeef)), 0);
+        send_to(payable(address(0xdeadbeef)), 0);
+
+        // 1 to EOA
+        transfer_to(payable(address(0xcafebabe)), 1);
+        send_to(payable(address(0xcafebabe)), 1);
+
+        BalanceReceiver balanceReceiver = new BalanceReceiver();
+
+        // 0 to contract
+        transfer_to(payable(address(balanceReceiver)), 0);
+        send_to(payable(address(balanceReceiver)), 0);
+
+        // 1 to contract
+        transfer_to(payable(address(balanceReceiver)), 1);
+        send_to(payable(address(balanceReceiver)), 1);
+    }
+
+    function transfer_to(address payable _dest, uint _amount) public payable {
+        _dest.transfer(_amount);
+    }
+
+    function send_to(address payable _dest, uint _amount) public payable {
+        require(_dest.send(_amount));
+    }
+}

crates/integration/contracts/Send.sol

@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8;
+
+/* runner.json
+{
+    "differential": false,
+    "actions": [
+        {
+            "Instantiate": {
+                "code": {
+                    "Solidity": {
+                        "contract": "Send"
+                    }
+                },
+                "value": 211
+            }
+        },
+        {
+            "Call": {
+                "dest": {
+                    "Instantiated": 0
+                },
+                "data": "1c8d16b30000000000000000000000000303030303030303030303030303030303030303000000000000000000000000000000000000000000000000000000000000000a"
+            }
+        },
+        {
+            "VerifyCall": {
+                "success": true
+            }
+        },
+        {
+            "Call": {
+                "dest": {
+                    "Instantiated": 0
+                },
+                "data": "fb9e8d050000000000000000000000000000000000000000000000000000000000000001"
+            }
+        },
+        {
+            "VerifyCall": {
+                "success": false
+            }
+        },
+        {
+            "Call": {
+                "dest": {
+                    "Instantiated": 0
+                },
+                "data": "fb9e8d050000000000000000000000000000000000000000000000000000000000000000"
+            }
+        },
+        {
+            "VerifyCall": {
+                "success": false
+            }
+        }
+    ]
+}
+*/
+
+contract Send {
+    constructor() payable {}
+
+    function transfer_self(uint _amount) public payable {
+        transfer_to(payable(address(this)), _amount);
+    }
+
+    function transfer_to(address payable _dest, uint _amount) public payable {
+        if (_dest.send(_amount)) {}
+    }
+
+    fallback() external {}
+
+    receive() external payable {}
+}

crates/integration/contracts/Transfer.sol

@@ -3,7 +3,7 @@ pragma solidity ^0.8;
 
 /* runner.json
 {
-    "differential": true,
+    "differential": false,
     "actions": [
         {
             "Instantiate": {
@@ -12,7 +12,7 @@ pragma solidity ^0.8;
                         "contract": "Transfer"
                     }
                 },
-                "value": 11
+                "value": 211
             }
         },
         {
@@ -23,12 +23,35 @@ pragma solidity ^0.8;
                 "data": "1c8d16b30000000000000000000000000303030303030303030303030303030303030303000000000000000000000000000000000000000000000000000000000000000a"
             }
         },
+        {
+            "VerifyCall": {
+                "success": true
+            }
+        },
         {
             "Call": {
                 "dest": {
                     "Instantiated": 0
                 },
-                "data": "fb9e8d0500000000000000000000000003030303030303030303030303030303030303030000000000000000000000000000000000000000000000000000000000000001"
+                "data": "fb9e8d050000000000000000000000000000000000000000000000000000000000000001"
+            }
+        },
+        {
+            "VerifyCall": {
+                "success": false
+            }
+        },
+        {
+            "Call": {
+                "dest": {
+                    "Instantiated": 0
+                },
+                "data": "fb9e8d050000000000000000000000000000000000000000000000000000000000000000"
+            }
+        },
+        {
+            "VerifyCall": {
+                "success": false
             }
         }
     ]
@@ -36,19 +59,17 @@ pragma solidity ^0.8;
 */
 
 contract Transfer {
-    constructor() payable {
+    constructor() payable {}
-        transfer_self(msg.value);
-    }
-
-    function address_self() internal view returns (address payable) {
-        return payable(address(this));
-    }
 
     function transfer_self(uint _amount) public payable {
-        transfer_to(address_self(), _amount);
+        transfer_to(payable(address(this)), _amount);
     }
 
     function transfer_to(address payable _dest, uint _amount) public payable {
         _dest.transfer(_amount);
     }
+
+    fallback() external {}
+
+    receive() external payable {}
 }

crates/integration/src/cases.rs

@@ -156,6 +156,20 @@ case!("DivisionArithmetics.sol", DivisionArithmetics, sdivCall, division_arithme
 case!("DivisionArithmetics.sol", DivisionArithmetics, modCall, division_arithmetics_mod, n: U256, d: U256);
 case!("DivisionArithmetics.sol", DivisionArithmetics, smodCall, division_arithmetics_smod, n: I256, d: I256);
 
+sol!(
+    contract Send {
+        function transfer_self(uint _amount) public payable;
+    }
+);
+case!("Send.sol", Send, transfer_selfCall, send_self, amount: U256);
+
+sol!(
+    contract Transfer {
+        function transfer_self(uint _amount) public payable;
+    }
+);
+case!("Transfer.sol", Transfer, transfer_selfCall, transfer_self, amount: U256);
+
 sol!(
     contract MStore8 {
         function mStore8(uint value) public pure returns (uint256 word);

crates/integration/src/tests.rs

@@ -37,10 +37,10 @@ test_spec!(events, "Events", "Events.sol");
 test_spec!(storage, "Storage", "Storage.sol");
 test_spec!(mstore8, "MStore8", "MStore8.sol");
 test_spec!(address, "Context", "Context.sol");
-test_spec!(balance, "Value", "Value.sol");
+test_spec!(value, "Value", "Value.sol");
 test_spec!(create, "CreateB", "Create.sol");
 test_spec!(call, "Caller", "Call.sol");
-test_spec!(transfer, "Transfer", "Transfer.sol");
+test_spec!(balance, "Balance", "Balance.sol");
 test_spec!(return_data_oob, "ReturnDataOob", "ReturnDataOob.sol");
 test_spec!(immutables, "Immutables", "Immutables.sol");
 test_spec!(transaction, "Transaction", "Transaction.sol");
@@ -52,6 +52,8 @@ test_spec!(gas_limit, "GasLimit", "GasLimit.sol");
 test_spec!(base_fee, "BaseFee", "BaseFee.sol");
 test_spec!(coinbase, "Coinbase", "Coinbase.sol");
 test_spec!(create2, "CreateB", "Create2.sol");
+test_spec!(transfer, "Transfer", "Transfer.sol");
+test_spec!(send, "Send", "Send.sol");
 
 fn instantiate(path: &str, contract: &str) -> Vec<SpecsAction> {
     vec![Instantiate {
@@ -434,3 +436,47 @@ fn ext_code_size() {
     }
     .run();
 }
+
+#[test]
+#[should_panic(expected = "ReentranceDenied")]
+fn send_denies_reentrancy() {
+    let value = 1000;
+    Specs {
+        actions: vec![
+            instantiate("contracts/Send.sol", "Send").remove(0),
+            Call {
+                origin: TestAddress::Alice,
+                dest: TestAddress::Instantiated(0),
+                value,
+                gas_limit: None,
+                storage_deposit_limit: None,
+                data: Contract::send_self(U256::from(value)).calldata,
+            },
+        ],
+        differential: false,
+        ..Default::default()
+    }
+    .run();
+}
+
+#[test]
+#[should_panic(expected = "ReentranceDenied")]
+fn transfer_denies_reentrancy() {
+    let value = 1000;
+    Specs {
+        actions: vec![
+            instantiate("contracts/Transfer.sol", "Transfer").remove(0),
+            Call {
+                origin: TestAddress::Alice,
+                dest: TestAddress::Instantiated(0),
+                value,
+                gas_limit: None,
+                storage_deposit_limit: None,
+                data: Contract::transfer_self(U256::from(value)).calldata,
+            },
+        ],
+        differential: false,
+        ..Default::default()
+    }
+    .run();
+}

crates/llvm-context/src/polkavm/evm/call.rs

@@ -8,6 +8,7 @@ use crate::polkavm::Dependency;
 
 const STATIC_CALL_FLAG: u32 = 0b0001_0000;
 const REENTRANT_CALL_FLAG: u32 = 0b0000_1000;
+const SOLIDITY_TRANSFER_GAS_STIPEND_THRESHOLD: u64 = 2300;
 
 /// Translates a contract call.
 #[allow(clippy::too_many_arguments)]
@@ -37,26 +38,24 @@ where
     let output_offset = context.safe_truncate_int_to_xlen(output_offset)?;
     let output_length = context.safe_truncate_int_to_xlen(output_length)?;
 
-    // TODO: What to supply here? Is there a weight to gas?
-    let _gas = context
-        .builder()
-        .build_int_truncate(gas, context.integer_type(64), "gas")?;
-
     let input_pointer = context.build_heap_gep(input_offset, input_length)?;
     let output_pointer = context.build_heap_gep(output_offset, output_length)?;
 
     let output_length_pointer = context.build_alloca_at_entry(context.xlen_type(), "output_length");
     context.build_store(output_length_pointer, output_length)?;
 
-    let deposit_pointer = context.build_alloca_at_entry(context.word_type(), "deposit_pointer");
+    let (flags, deposit_limit_value) = if static_call {
-    context.build_store(deposit_pointer, context.word_type().const_all_ones())?;
+        let flags = REENTRANT_CALL_FLAG | STATIC_CALL_FLAG;
-
+        (
-    let flags = if static_call {
+            context.xlen_type().const_int(flags as u64, false),
-        REENTRANT_CALL_FLAG | STATIC_CALL_FLAG
+            context.word_type().const_zero(),
+        )
     } else {
-        REENTRANT_CALL_FLAG
+        call_reentrancy_heuristic(context, gas, input_length, output_length)?
     };
-    let flags = context.xlen_type().const_int(flags as u64, false);
+
+    let deposit_pointer = context.build_alloca_at_entry(context.word_type(), "deposit_pointer");
+    context.build_store(deposit_pointer, deposit_limit_value)?;
 
     let flags_and_callee = revive_runtime_api::calling_convention::pack_hi_lo_reg(
         context.builder(),
@@ -119,7 +118,7 @@ where
 #[allow(clippy::too_many_arguments)]
 pub fn delegate_call<'ctx, D>(
     context: &mut Context<'ctx, D>,
-    gas: inkwell::values::IntValue<'ctx>,
+    _gas: inkwell::values::IntValue<'ctx>,
     address: inkwell::values::IntValue<'ctx>,
     input_offset: inkwell::values::IntValue<'ctx>,
     input_length: inkwell::values::IntValue<'ctx>,
@@ -137,11 +136,6 @@ where
     let output_offset = context.safe_truncate_int_to_xlen(output_offset)?;
     let output_length = context.safe_truncate_int_to_xlen(output_length)?;
 
-    // TODO: What to supply here? Is there a weight to gas?
-    let _gas = context
-        .builder()
-        .build_int_truncate(gas, context.integer_type(64), "gas")?;
-
     let input_pointer = context.build_heap_gep(input_offset, input_length)?;
     let output_pointer = context.build_heap_gep(output_offset, output_length)?;
 
@@ -221,3 +215,86 @@ where
         .resolve_library(path.as_str())?
         .as_basic_value_enum())
 }
+
+/// The Solidity `address.transfer` and `address.send` call detection heuristic.
+///
+/// # Why
+/// This heuristic is an additional security feature to guard against re-entrancy attacks
+/// in case contract authors violate Solidity best practices and use `address.transfer` or
+/// `address.send`.
+/// While contract authors are supposed to never use `address.transfer` or `address.send`,
+/// for a small cost we can be extra defensive about it.
+///
+/// # How
+/// The gas stipend emitted by solc for `transfer` and `send` is not static, thus:
+/// - Dynamically allow re-entrancy only for calls considered not transfer or send.
+/// - Detected balance transfers will supply 0 deposit limit instead of `u256::MAX`.
+///
+/// Calls are considered transfer or send if:
+/// - (Input length | Output lenght) == 0;
+/// - Gas <= 2300;
+///
+/// # Returns
+/// The call flags xlen `IntValue` and the deposit limit word `IntValue`.
+fn call_reentrancy_heuristic<'ctx, D>(
+    context: &mut Context<'ctx, D>,
+    gas: inkwell::values::IntValue<'ctx>,
+    input_length: inkwell::values::IntValue<'ctx>,
+    output_length: inkwell::values::IntValue<'ctx>,
+) -> anyhow::Result<(
+    inkwell::values::IntValue<'ctx>,
+    inkwell::values::IntValue<'ctx>,
+)>
+where
+    D: Dependency + Clone,
+{
+    // Branch-free SSA implementation: First derive the heuristic boolean (int1) value.
+    let input_length_or_output_length =
+        context
+            .builder()
+            .build_or(input_length, output_length, "input_length_or_output_length")?;
+    let is_no_input_no_output = context.builder().build_int_compare(
+        inkwell::IntPredicate::EQ,
+        context.xlen_type().const_zero(),
+        input_length_or_output_length,
+        "is_no_input_no_output",
+    )?;
+    let gas_stipend = context
+        .word_type()
+        .const_int(SOLIDITY_TRANSFER_GAS_STIPEND_THRESHOLD, false);
+    let is_gas_stipend_for_transfer_or_send = context.builder().build_int_compare(
+        inkwell::IntPredicate::ULE,
+        gas,
+        gas_stipend,
+        "is_gas_stipend_for_transfer_or_send",
+    )?;
+    let is_balance_transfer = context.builder().build_and(
+        is_no_input_no_output,
+        is_gas_stipend_for_transfer_or_send,
+        "is_balance_transfer",
+    )?;
+    let is_regular_call = context
+        .builder()
+        .build_not(is_balance_transfer, "is_balance_transfer_inverted")?;
+
+    // Call flag: Left shift the heuristic boolean value.
+    let is_regular_call_xlen = context.builder().build_int_z_extend(
+        is_regular_call,
+        context.xlen_type(),
+        "is_balance_transfer_xlen",
+    )?;
+    let call_flags = context.builder().build_left_shift(
+        is_regular_call_xlen,
+        context.xlen_type().const_int(3, false),
+        "flags",
+    )?;
+
+    // Deposit limit value: Sign-extended the heuristic boolean value.
+    let deposit_limit_value = context.builder().build_int_s_extend(
+        is_regular_call,
+        context.word_type(),
+        "deposit_limit_value",
+    )?;
+
+    Ok((call_flags, deposit_limit_value))
+}

crates/solidity/src/solc/standard_json/output/error/mod.rs

@@ -54,11 +54,14 @@ implement other signature schemes.
     /// Returns the `<address payable>`'s `send` and `transfer` methods usage error.
     pub fn message_send_and_transfer(src: Option<&str>) -> Self {
         let message = r#"
-Warning: It looks like you are using '<address payable>.send/transfer(<X>)'. Such balance
+Warning: It looks like you are using '<address payable>.send/transfer(<X>)'.
-transfer calls will supply all remaining gas and disable call re-entrancy instead of
+Using '<address payable>.send/transfer(<X>)' is deprecated and strongly discouraged!
-supplying the 2300 gas stipend. However, the compiler uses a heuristic to detect the expected
+The resolc compiler uses a heuristic to detect '<address payable>.send/transfer(<X>)' calls,
-2300 gas stipend. You are advised to carefully test this to ensure the desired behavior.
+which disables call re-entrancy and supplies all remaining gas instead of the 2300 gas stipend.
+However, detection is not guaranteed. You are advised to carefully test this, employ
+re-entrancy guards or use the withdrawal pattern instead!
 Learn more on https://docs.soliditylang.org/en/latest/security-considerations.html#reentrancy
+and https://docs.soliditylang.org/en/latest/common-patterns.html#withdrawal-from-contracts
 "#
         .to_owned();