[contracts] Add per local weight for function call (paritytech#12806)

* Add per local weight for function call

* ".git/.scripts/bench-bot.sh" pallet dev pallet_contracts

* Update frame/contracts/src/benchmarking/mod.rs

Co-authored-by: Alexander Theißen <alex.theissen@me.com>

* apply suggestions from code review

* ".git/.scripts/bench-bot.sh" pallet dev pallet_contracts

* Update frame/contracts/src/benchmarking/mod.rs

Co-authored-by: Alexander Theißen <alex.theissen@me.com>

* tune the benchmark

* ".git/.scripts/bench-bot.sh" pallet dev pallet_contracts

* fix benches

* ".git/.scripts/bench-bot.sh" pallet dev pallet_contracts

Co-authored-by: command-bot <>
Co-authored-by: Alexander Theißen <alex.theissen@me.com>

frame/contracts/Cargo.toml

@@ -20,7 +20,7 @@ codec = { package = "parity-scale-codec", version = "3.0.0", default-features =
 ] }
 scale-info = { version = "2.1.1", default-features = false, features = ["derive"] }
 log = { version = "0.4", default-features = false }
-wasm-instrument = { version = "0.3", default-features = false }
+wasm-instrument = { version = "0.4", default-features = false }
 serde = { version = "1", optional = true, features = ["derive"] }
 smallvec = { version = "1", default-features = false, features = [
 	"const_generics",

frame/contracts/src/benchmarking/code.rs

@@ -29,11 +29,14 @@ use frame_support::traits::Get;
 use sp_core::crypto::UncheckedFrom;
 use sp_runtime::traits::Hash;
 use sp_std::{borrow::ToOwned, prelude::*};
-use wasm_instrument::parity_wasm::{
-	builder,
-	elements::{
-		self, BlockType, CustomSection, External, FuncBody, Instruction, Instructions, Module,
-		Section, ValueType,
+use wasm_instrument::{
+	gas_metering,
+	parity_wasm::{
+		builder,
+		elements::{
+			self, BlockType, CustomSection, External, FuncBody, Instruction, Instructions, Module,
+			Section, ValueType,
+		},
 	},
 };
 
@@ -541,7 +544,8 @@ where
 fn inject_gas_metering<T: Config>(module: Module) -> Module {
 	let schedule = T::Schedule::get();
 	let gas_rules = schedule.rules(&module, Determinism::Deterministic);
-	wasm_instrument::gas_metering::inject(module, &gas_rules, "seal0").unwrap()
+	let backend = gas_metering::host_function::Injector::new("seal0", "gas");
+	gas_metering::inject(module, backend, &gas_rules).unwrap()
 }
 
 fn inject_stack_metering<T: Config>(module: Module) -> Module {

frame/contracts/src/benchmarking/mod.rs

@@ -2429,10 +2429,28 @@ benchmarks! {
 		sbox.invoke();
 	}
 
+	// w_per_local = w_bench
+	instr_call_per_local {
+		let l in 0 .. T::Schedule::get().limits.locals;
+		let mut aux_body = body::plain(vec![
+			Instruction::End,
+		]);
+		body::inject_locals(&mut aux_body, l);
+		let mut sbox = Sandbox::from(&WasmModule::<T>::from(ModuleDefinition {
+			aux_body: Some(aux_body),
+			call_body: Some(body::repeated(INSTR_BENCHMARK_BATCH_SIZE, &[
+				Instruction::Call(2), // call aux
+			])),
+			.. Default::default()
+		}));
+	}: {
+		sbox.invoke();
+	}
+
 	// w_local_get = w_bench - 1 * w_param
 	instr_local_get {
 		let r in 0 .. INSTR_BENCHMARK_BATCHES;
-		let max_locals = T::Schedule::get().limits.stack_height.unwrap_or(512);
+		let max_locals = T::Schedule::get().limits.locals;
 		let mut call_body = body::repeated_dyn(r * INSTR_BENCHMARK_BATCH_SIZE, vec![
 			RandomGetLocal(0, max_locals),
 			Regular(Instruction::Drop),
@@ -2449,7 +2467,7 @@ benchmarks! {
 	// w_local_set = w_bench - 1 * w_param
 	instr_local_set {
 		let r in 0 .. INSTR_BENCHMARK_BATCHES;
-		let max_locals = T::Schedule::get().limits.stack_height.unwrap_or(512);
+		let max_locals = T::Schedule::get().limits.locals;
 		let mut call_body = body::repeated_dyn(r * INSTR_BENCHMARK_BATCH_SIZE, vec![
 			RandomI64Repeated(1),
 			RandomSetLocal(0, max_locals),
@@ -2466,7 +2484,7 @@ benchmarks! {
 	// w_local_tee = w_bench - 2 * w_param
 	instr_local_tee {
 		let r in 0 .. INSTR_BENCHMARK_BATCHES;
-		let max_locals = T::Schedule::get().limits.stack_height.unwrap_or(512);
+		let max_locals = T::Schedule::get().limits.locals;
 		let mut call_body = body::repeated_dyn(r * INSTR_BENCHMARK_BATCH_SIZE, vec![
 			RandomI64Repeated(1),
 			RandomTeeLocal(0, max_locals),

frame/contracts/src/schedule.rs

@@ -118,6 +118,12 @@ pub struct Limits {
 	/// the linear memory limit `memory_pages` applies to them.
 	pub globals: u32,
 
+	/// Maximum number of locals a function can have.
+	///
+	/// As wasm engine initializes each of the local, we need to limit their number to confine
+	/// execution costs.
+	pub locals: u32,
+
 	/// Maximum numbers of parameters a function can have.
 	///
 	/// Those need to be limited to prevent a potentially exploitable interaction with
@@ -212,6 +218,7 @@ pub struct InstructionWeights<T: Config> {
 	pub call: u32,
 	pub call_indirect: u32,
 	pub call_indirect_per_param: u32,
+	pub call_per_local: u32,
 	pub local_get: u32,
 	pub local_set: u32,
 	pub local_tee: u32,
@@ -522,6 +529,7 @@ impl Default for Limits {
 			// No stack limit required because we use a runtime resident execution engine.
 			stack_height: None,
 			globals: 256,
+			locals: 1024,
 			parameters: 128,
 			memory_pages: 16,
 			// 4k function pointers (This is in count not bytes).
@@ -552,6 +560,7 @@ impl<T: Config> Default for InstructionWeights<T> {
 			call: cost_instr!(instr_call, 2),
 			call_indirect: cost_instr!(instr_call_indirect, 3),
 			call_indirect_per_param: cost_instr!(instr_call_indirect_per_param, 1),
+			call_per_local: cost_instr!(instr_call_per_local, 1),
 			local_get: cost_instr!(instr_local_get, 1),
 			local_set: cost_instr!(instr_local_set, 1),
 			local_tee: cost_instr!(instr_local_tee, 2),
@@ -792,6 +801,10 @@ impl<'a, T: Config> gas_metering::Rules for ScheduleRules<'a, T> {
 		// The cost for growing is therefore already included in the instruction cost.
 		gas_metering::MemoryGrowCost::Free
 	}
+
+	fn call_per_local_cost(&self) -> u32 {
+		self.schedule.instruction_weights.call_per_local
+	}
 }
 
 #[cfg(test)]

frame/contracts/src/wasm/prepare.rs

@@ -29,8 +29,9 @@ use codec::{Encode, MaxEncodedLen};
 use sp_core::crypto::UncheckedFrom;
 use sp_runtime::{traits::Hash, DispatchError};
 use sp_std::prelude::*;
-use wasm_instrument::parity_wasm::elements::{
-	self, External, Internal, MemoryType, Type, ValueType,
+use wasm_instrument::{
+	gas_metering,
+	parity_wasm::elements::{self, External, Internal, MemoryType, Type, ValueType},
 };
 use wasmi::StackLimits;
 use wasmparser::{Validator, WasmFeatures};
@@ -132,6 +133,19 @@ impl<'a, T: Config> ContractModule<'a, T> {
 		Ok(())
 	}
 
+	fn ensure_local_variable_limit(&self, limit: u32) -> Result<(), &'static str> {
+		if let Some(code_section) = self.module.code_section() {
+			for func_body in code_section.bodies() {
+				let locals_count: u32 =
+					func_body.locals().iter().map(|val_type| val_type.count()).sum();
+				if locals_count > limit {
+					return Err("single function declares too many locals")
+				}
+			}
+		}
+		Ok(())
+	}
+
 	/// Ensures that no floating point types are in use.
 	fn ensure_no_floating_types(&self) -> Result<(), &'static str> {
 		if let Some(global_section) = self.module.global_section() {
@@ -197,9 +211,9 @@ impl<'a, T: Config> ContractModule<'a, T> {
 
 	fn inject_gas_metering(self, determinism: Determinism) -> Result<Self, &'static str> {
 		let gas_rules = self.schedule.rules(&self.module, determinism);
-		let contract_module =
-			wasm_instrument::gas_metering::inject(self.module, &gas_rules, "seal0")
-				.map_err(|_| "gas instrumentation failed")?;
+		let backend = gas_metering::host_function::Injector::new("seal0", "gas");
+		let contract_module = gas_metering::inject(self.module, backend, &gas_rules)
+			.map_err(|_| "gas instrumentation failed")?;
 		Ok(ContractModule { module: contract_module, schedule: self.schedule })
 	}
 
@@ -422,6 +436,7 @@ where
 		contract_module.ensure_no_internal_memory()?;
 		contract_module.ensure_table_size_limit(schedule.limits.table_size)?;
 		contract_module.ensure_global_variable_limit(schedule.limits.globals)?;
+		contract_module.ensure_local_variable_limit(schedule.limits.locals)?;
 		contract_module.ensure_parameter_limit(schedule.limits.parameters)?;
 		contract_module.ensure_br_table_size_limit(schedule.limits.br_table_size)?;
 
@@ -636,7 +651,8 @@ mod tests {
 				let wasm = wat::parse_str($wat).unwrap().try_into().unwrap();
 				let schedule = Schedule {
 					limits: Limits {
-						globals: 3,
+					    globals: 3,
+					    locals: 3,
 						parameters: 3,
 						memory_pages: 16,
 						table_size: 3,
@@ -736,6 +752,43 @@ mod tests {
 		);
 	}
 
+	mod locals {
+		use super::*;
+
+		prepare_test!(
+			local_number_valid,
+			r#"
+			(module
+				(func
+					(local i32)
+					(local i32)
+					(local i32)
+				)
+				(func (export "call"))
+				(func (export "deploy"))
+			)
+			"#,
+			Ok(_)
+		);
+
+		prepare_test!(
+			local_number_too_high,
+			r#"
+			(module
+				(func
+					(local i32)
+					(local i32)
+					(local i32)
+					(local i32)
+				)
+				(func (export "call"))
+				(func (export "deploy"))
+			)
+			"#,
+			Err("single function declares too many locals")
+		);
+	}
+
 	mod memories {
 		use super::*;