Gas counting changes: allow memory words counter not greater than gas max (int64 max)

libevmjit-cpp/JitVM.cpp

@@ -16,6 +16,7 @@ bytesConstRef JitVM::go(ExtVMFace& _ext, OnOpFunc const& _onOp, uint64_t _step)
 	using namespace jit;
 
 	auto rejected = false;
+	// TODO: Rejecting transactions with gas limit > 2^63 can be used by attacker to take JIT out of scope
 	rejected |= m_gas > std::numeric_limits<decltype(m_data.gas)>::max(); // Do not accept requests with gas > 2^63 (int64 max)
 	rejected |= _ext.gasPrice > std::numeric_limits<decltype(m_data.gasPrice)>::max();
 	rejected |= _ext.currentBlock.number > std::numeric_limits<decltype(m_data.number)>::max();

libevmjit/GasMeter.cpp

@@ -94,12 +94,13 @@ GasMeter::GasMeter(llvm::IRBuilder<>& _builder, RuntimeManager& _runtimeManager)
 	auto outOfGasBB = llvm::BasicBlock::Create(_builder.getContext(), "OutOfGas", m_gasCheckFunc);
 	auto updateBB = llvm::BasicBlock::Create(_builder.getContext(), "Update", m_gasCheckFunc);
 
-	m_builder.SetInsertPoint(checkBB);
 	auto arg = m_gasCheckFunc->arg_begin();
 	arg->setName("rt");
 	++arg;
 	arg->setName("cost");
 	auto cost = arg;
+
+	m_builder.SetInsertPoint(checkBB);
 	auto gas = m_runtimeManager.getGas();
 	auto isOutOfGas = m_builder.CreateICmpUGT(cost, gas, "isOutOfGas");
 	m_builder.CreateCondBr(isOutOfGas, outOfGasBB, updateBB);
@@ -208,8 +209,14 @@ void GasMeter::commitCostBlock()
 
 void GasMeter::countMemory(llvm::Value* _additionalMemoryInWords)
 {
+	assert(_additionalMemoryInWords->getType() == Type::Word);
 	static_assert(c_memoryGas == 1, "Memory gas cost has changed. Update GasMeter.");
-	count(_additionalMemoryInWords);
+	auto gasMax256 = m_builder.CreateZExt(Constant::gasMax, Type::Word);
+	auto tooHigh = m_builder.CreateICmpUGT(_additionalMemoryInWords, gasMax256, "tooHigh");
+	auto additionalMemoryInWords64 = m_builder.CreateTrunc(_additionalMemoryInWords, Type::Gas);
+	additionalMemoryInWords64 = m_builder.CreateSelect(tooHigh, Constant::gasMax, additionalMemoryInWords64, "additionalMemoryInWords");
+	auto additionalMemoryInWords256 = m_builder.CreateZExt(additionalMemoryInWords64, Type::Word);
+	count(additionalMemoryInWords256);
 }
 
 void GasMeter::countCopy(llvm::Value* _copyWords)

libevmjit/Type.cpp

@@ -17,6 +17,7 @@ llvm::PointerType* Type::WordPtr;
 llvm::IntegerType* Type::lowPrecision;
 llvm::IntegerType* Type::Bool;
 llvm::IntegerType* Type::Size;
+llvm::IntegerType* Type::Gas;
 llvm::IntegerType* Type::Byte;
 llvm::PointerType* Type::BytePtr;
 llvm::Type* Type::Void;
@@ -24,6 +25,7 @@ llvm::IntegerType* Type::MainReturn;
 llvm::PointerType* Type::EnvPtr;
 llvm::PointerType* Type::RuntimeDataPtr;
 llvm::PointerType* Type::RuntimePtr;
+llvm::ConstantInt* Constant::gasMax;
 
 void Type::init(llvm::LLVMContext& _context)
 {
@@ -35,6 +37,7 @@ void Type::init(llvm::LLVMContext& _context)
 		// TODO: Size should be architecture-dependent
 		Bool = llvm::Type::getInt1Ty(_context);
 		Size = llvm::Type::getInt64Ty(_context);
+		Gas = Size;
 		Byte = llvm::Type::getInt8Ty(_context);
 		BytePtr = Byte->getPointerTo();
 		Void = llvm::Type::getVoidTy(_context);
@@ -43,6 +46,8 @@ void Type::init(llvm::LLVMContext& _context)
 		EnvPtr = llvm::StructType::create(_context, "Env")->getPointerTo();
 		RuntimeDataPtr = RuntimeManager::getRuntimeDataType()->getPointerTo();
 		RuntimePtr = RuntimeManager::getRuntimeType()->getPointerTo();
+
+		Constant::gasMax = llvm::ConstantInt::getSigned(Type::Gas, std::numeric_limits<int64_t>::max());
 	}
 }
 

libevmjit/Type.h

@@ -23,6 +23,7 @@ struct Type
 
 	static llvm::IntegerType* Bool;
 	static llvm::IntegerType* Size;
+	static llvm::IntegerType* Gas;
 
 	static llvm::IntegerType* Byte;
 	static llvm::PointerType* BytePtr;
@@ -41,6 +42,8 @@ struct Type
 
 struct Constant
 {
+	static llvm::ConstantInt* gasMax;
+
 	/// Returns word-size constant
 	static llvm::ConstantInt* get(int64_t _n);
 	static llvm::ConstantInt* get(llvm::APInt const& _n);