contracts: Allow indeterministic instructions off-chain (paritytech#1…

…2469)

* Allow indetermistic instructions off-chain

* Apply suggestions from code review

Co-authored-by: Sasha Gryaznov <hi@agryaznov.com>

* fmt

Co-authored-by: Sasha Gryaznov <hi@agryaznov.com>

bin/node/runtime/src/lib.rs

@@ -1959,7 +1959,16 @@ impl_runtime_apis! {
 			input_data: Vec<u8>,
 		) -> pallet_contracts_primitives::ContractExecResult<Balance> {
 			let gas_limit = gas_limit.unwrap_or(RuntimeBlockWeights::get().max_block);
-			Contracts::bare_call(origin, dest, value, gas_limit, storage_deposit_limit, input_data, true)
+			Contracts::bare_call(
+				origin,
+				dest,
+				value,
+				gas_limit,
+				storage_deposit_limit,
+				input_data,
+				true,
+				pallet_contracts::Determinism::Deterministic,
+			)
 		}
 
 		fn instantiate(
@@ -1973,23 +1982,41 @@ impl_runtime_apis! {
 		) -> pallet_contracts_primitives::ContractInstantiateResult<AccountId, Balance>
 		{
 			let gas_limit = gas_limit.unwrap_or(RuntimeBlockWeights::get().max_block);
-			Contracts::bare_instantiate(origin, value, gas_limit, storage_deposit_limit, code, data, salt, true)
+			Contracts::bare_instantiate(
+				origin,
+				value,
+				gas_limit,
+				storage_deposit_limit,
+				code,
+				data,
+				salt,
+				true
+			)
 		}
 
 		fn upload_code(
 			origin: AccountId,
 			code: Vec<u8>,
 			storage_deposit_limit: Option<Balance>,
+			determinism: pallet_contracts::Determinism,
 		) -> pallet_contracts_primitives::CodeUploadResult<Hash, Balance>
 		{
-			Contracts::bare_upload_code(origin, code, storage_deposit_limit)
+			Contracts::bare_upload_code(
+				origin,
+				code,
+				storage_deposit_limit,
+				determinism,
+			)
 		}
 
 		fn get_storage(
 			address: AccountId,
 			key: Vec<u8>,
 		) -> pallet_contracts_primitives::GetStorageResult {
-			Contracts::get_storage(address, key)
+			Contracts::get_storage(
+				address,
+				key
+			)
 		}
 	}
 

frame/contracts/README.md

@@ -37,12 +37,37 @@ changes still persist.
 One gas is equivalent to one [weight](https://docs.substrate.io/v3/runtime/weights-and-fees)
 which is defined as one picosecond of execution time on the runtime's reference machine.
 
-### Notable Scenarios
+### Revert Behaviour
 
-Contract call failures are not always cascading. When failures occur in a sub-call, they do not "bubble up",
+Contract call failures are not cascading. When failures occur in a sub-call, they do not "bubble up",
 and the call will only revert at the specific contract level. For example, if contract A calls contract B, and B
 fails, A can decide how to handle that failure, either proceeding or reverting A's changes.
 
+### Offchain Execution
+
+In general, a contract execution needs to be deterministic so that all nodes come to the same
+conclusion when executing it. To that end we disallow any instructions that could cause
+indeterminism. Most notable are any floating point arithmetic. That said, sometimes contracts
+are executed off-chain and hence are not subject to consensus. If code is only executed by a
+single node and implicitly trusted by other actors is such a case. Trusted execution environments
+come to mind. To that end we allow the execution of indeterminstic code for offchain usages
+with the following constraints:
+
+1. No contract can ever be instantiated from an indeterministic code. The only way to execute
+the code is to use a delegate call from a deterministic contract.
+2. The code that wants to use this feature needs to depend on `pallet-contracts` and use `bare_call`
+directly. This makes sure that by default `pallet-contracts` does not expose any indeterminism.
+
+## How to use
+
+When setting up the `Schedule` for your runtime make sure to set `InstructionWeights::fallback`
+to a non zero value. The default is `0` and prevents the upload of any non deterministic code.
+
+An indeterministic code can be deployed on-chain by passing `Determinism::AllowIndeterministic`
+to `upload_code`. A determinstic contract can then delegate call into it if and only if it
+is ran by using `bare_call` and passing `Determinism::AllowIndeterministic` to it. **Never use
+this argument when the contract is called from an on-chain transaction.**
+
 ## Interface
 
 ### Dispatchable functions

frame/contracts/fixtures/delegate_call_simple.wat

@@ -0,0 +1,50 @@
+;; Just delegate call into the passed code hash and assert success.
+(module
+	(import "seal0" "seal_input" (func $seal_input (param i32 i32)))
+	(import "seal0" "seal_delegate_call" (func $seal_delegate_call (param i32 i32 i32 i32 i32 i32) (result i32)))
+	(import "env" "memory" (memory 3 3))
+
+	;; [0, 32) buffer where input is copied
+
+	;; [32, 36) size of the input buffer
+	(data (i32.const 32) "\20")
+
+	(func $assert (param i32)
+		(block $ok
+			(br_if $ok
+				(get_local 0)
+			)
+			(unreachable)
+		)
+	)
+
+	(func (export "call")
+		;; Reading "callee" code_hash
+		(call $seal_input (i32.const 0) (i32.const 32))
+
+		;; assert input size == 32
+		(call $assert
+			(i32.eq
+				(i32.load (i32.const 32))
+				(i32.const 32)
+			)
+		)
+
+		;; Delegate call into passed code hash
+		(call $assert
+			(i32.eq
+				(call $seal_delegate_call
+					(i32.const 0)	;; Set no call flags
+					(i32.const 0)	;; Pointer to "callee" code_hash.
+					(i32.const 0)	;; Input is ignored
+					(i32.const 0)	;; Length of the input
+					(i32.const 4294967295)	;; u32 max sentinel value: do not copy output
+					(i32.const 0)	;; Length is ignored in this case
+				)
+				(i32.const 0)
+			)
+		)
+	)
+
+	(func (export "deploy"))
+)

frame/contracts/fixtures/float_instruction.wat

@@ -0,0 +1,11 @@
+;; Module that contains a float instruction which is illegal in deterministic mode
+(module
+	(func (export "call")
+		f32.const 1
+		drop
+	)
+	(func (export "deploy")
+		f32.const 2
+        drop
+	)
+)

frame/contracts/src/benchmarking/code.rs

@@ -24,7 +24,7 @@
 //! we define this simple definition of a contract that can be passed to `create_code` that
 //! compiles it down into a `WasmModule` that can be used as a contract's code.
 
-use crate::Config;
+use crate::{Config, Determinism};
 use frame_support::traits::Get;
 use sp_core::crypto::UncheckedFrom;
 use sp_runtime::traits::Hash;
@@ -554,7 +554,7 @@ where
 
 fn inject_gas_metering<T: Config>(module: Module) -> Module {
 	let schedule = T::Schedule::get();
-	let gas_rules = schedule.rules(&module);
+	let gas_rules = schedule.rules(&module, Determinism::Deterministic);
 	wasm_instrument::gas_metering::inject(module, &gas_rules, "seal0").unwrap()
 }
 

frame/contracts/src/benchmarking/mod.rs

@@ -371,7 +371,7 @@ benchmarks! {
 		T::Currency::make_free_balance_be(&caller, caller_funding::<T>());
 		let WasmModule { code, hash, .. } = WasmModule::<T>::sized(c, Location::Call);
 		let origin = RawOrigin::Signed(caller.clone());
-	}: _(origin, code, None)
+	}: _(origin, code, None, Determinism::Deterministic)
 	verify {
 		// uploading the code reserves some balance in the callers account
 		assert!(T::Currency::reserved_balance(&caller) > 0u32.into());
@@ -386,7 +386,7 @@ benchmarks! {
 		T::Currency::make_free_balance_be(&caller, caller_funding::<T>());
 		let WasmModule { code, hash, .. } = WasmModule::<T>::dummy();
 		let origin = RawOrigin::Signed(caller.clone());
-		let uploaded = <Contracts<T>>::bare_upload_code(caller.clone(), code, None)?;
+		let uploaded = <Contracts<T>>::bare_upload_code(caller.clone(), code, None, Determinism::Deterministic)?;
 		assert_eq!(uploaded.code_hash, hash);
 		assert_eq!(uploaded.deposit, T::Currency::reserved_balance(&caller));
 		assert!(<Contract<T>>::code_exists(&hash));
@@ -2894,6 +2894,7 @@ benchmarks! {
 			None,
 			data,
 			false,
+			Determinism::Deterministic,
 		)
 		.result?;
 	}
@@ -2941,6 +2942,7 @@ benchmarks! {
 			None,
 			data,
 			false,
+			Determinism::Deterministic,
 		)
 		.result?;
 	}