Make parachain validation wasm executor functional (#1574)

* Make parachain validation wasm executor functional

- Increase the size of the validation result in the shared memory. The
validation result holds the new runtime when a runtime upgrade is
scheduled. So, we need to give it enough memory to send the data between
the validator and the wasm execution host.
- Add the `CallInWasmExt`. This is required when doing a runtime upgrade
to check that we upgrade to something meaningful.

* Update parachain/src/wasm_executor/mod.rs

* Update parachain/src/wasm_executor/mod.rs

Co-authored-by: Nikolay Volf <nikvolf@gmail.com>

Co-authored-by: Nikolay Volf <nikvolf@gmail.com>

parachain/src/wasm_executor/mod.rs

@@ -35,6 +35,7 @@ mod validation_host;
 // maximum memory in bytes
 const MAX_RUNTIME_MEM: usize = 1024 * 1024 * 1024; // 1 GiB
 const MAX_CODE_MEM: usize = 16 * 1024 * 1024; // 16 MiB
+const MAX_VALIDATION_RESULT_HEADER_MEM: usize = MAX_CODE_MEM + 1024; // 16.001 MiB
 
 /// A stub validation-pool defined when compiling for Android or WASM.
 #[cfg(any(target_os = "android", target_os = "unknown"))]
@@ -176,11 +177,6 @@ pub fn validate_candidate_internal(
 	encoded_call_data: &[u8],
 	spawner: impl SpawnNamed + 'static,
 ) -> Result<ValidationResult, ValidationError> {
-	let mut extensions = Extensions::new();
-	extensions.register(sp_core::traits::TaskExecutorExt::new(spawner));
-
-	let mut ext = ValidationExternalities(extensions);
-
 	let executor = sc_executor::WasmExecutor::new(
 		sc_executor::WasmExecutionMethod::Interpreted,
 		// TODO: Make sure we don't use more than 1GB: https://github.com/paritytech/polkadot/issues/699
@@ -188,6 +184,13 @@ pub fn validate_candidate_internal(
 		HostFunctions::host_functions(),
 		8
 	);
+
+	let mut extensions = Extensions::new();
+	extensions.register(sp_core::traits::TaskExecutorExt::new(spawner));
+	extensions.register(sp_core::traits::CallInWasmExt::new(executor.clone()));
+
+	let mut ext = ValidationExternalities(extensions);
+
 	let res = executor.call_in_wasm(
 		validation_code,
 		None,

parachain/src/wasm_executor/validation_host.rs

@@ -19,8 +19,10 @@
 use std::{process, env, sync::Arc, sync::atomic};
 use codec::{Decode, Encode};
 use crate::primitives::{ValidationParams, ValidationResult};
-use super::{validate_candidate_internal, ValidationError, InvalidCandidate, InternalError,
-			MAX_CODE_MEM, MAX_RUNTIME_MEM};
+use super::{
+	validate_candidate_internal, ValidationError, InvalidCandidate, InternalError,
+	MAX_CODE_MEM, MAX_RUNTIME_MEM, MAX_VALIDATION_RESULT_HEADER_MEM,
+};
 use shared_memory::{SharedMem, SharedMemConf, EventState, WriteLockable, EventWait, EventSet};
 use parking_lot::Mutex;
 use log::{debug, trace};
@@ -113,7 +115,7 @@ pub fn run_worker(mem_id: &str) -> Result<(), String> {
 	};
 
 	let exit = Arc::new(atomic::AtomicBool::new(false));
-    let task_executor = TaskExecutor::new()?;
+	let task_executor = TaskExecutor::new()?;
 	// spawn parent monitor thread
 	let watch_exit = exit.clone();
 	std::thread::spawn(move || {
@@ -220,7 +222,7 @@ impl Drop for ValidationHost {
 
 impl ValidationHost {
 	fn create_memory() -> Result<SharedMem, InternalError> {
-		let mem_size = MAX_RUNTIME_MEM + MAX_CODE_MEM + 1024;
+		let mem_size = MAX_RUNTIME_MEM + MAX_CODE_MEM + MAX_VALIDATION_RESULT_HEADER_MEM;
 		let mem_config = SharedMemConf::default()
 			.set_size(mem_size)
 			.add_lock(shared_memory::LockType::Mutex, 0, mem_size)?
@@ -318,9 +320,16 @@ impl ValidationHost {
 			debug!("{} Reading results", self.id);
 			let data: &[u8] = &**memory.wlock_as_slice(0)
 				.map_err(|e| ValidationError::Internal(e.into()))?;
-			let (header_buf, _) = data.split_at(1024);
+			let (header_buf, _) = data.split_at(MAX_VALIDATION_RESULT_HEADER_MEM);
 			let mut header_buf: &[u8] = header_buf;
-			let header = ValidationResultHeader::decode(&mut header_buf).unwrap();
+			let header = ValidationResultHeader::decode(&mut header_buf)
+				.map_err(|e|
+					InternalError::System(
+						Box::<dyn std::error::Error + Send + Sync>::from(
+							format!("Failed to decode `ValidationResultHeader`: {:?}", e)
+						) as Box<_>
+					)
+				)?;
 			match header {
 				ValidationResultHeader::Ok(result) => Ok(result),
 				ValidationResultHeader::Error(WorkerValidationError::InternalError(e)) => {