Sort out validation errors (#1516)

* Sort out validation errors

* Typo

* Fixed wasm/android build

* Fixed bad merge

node/core/backing/src/lib.rs

@@ -305,7 +305,7 @@ impl CandidateBackingJob {
 					}
 				}
 			}
-			ValidationResult::Invalid => {
+			ValidationResult::Invalid(_reason) => {
 				// no need to issue a statement about this if we aren't seconding it.
 				//
 				// there's an infinite amount of garbage out there. no need to acknowledge
@@ -497,7 +497,7 @@ impl CandidateBackingJob {
 					Err(()) => Statement::Invalid(candidate_hash),
 				}
 			}
-			ValidationResult::Invalid => {
+			ValidationResult::Invalid(_reason) => {
 				Statement::Invalid(candidate_hash)
 			}
 		};
@@ -826,6 +826,7 @@ mod tests {
 		messages::RuntimeApiRequest,
 		ActiveLeavesUpdate, FromOverseer, OverseerSignal,
 	};
+	use polkadot_node_primitives::InvalidCandidate;
 	use sp_keyring::Sr25519Keyring;
 	use std::collections::HashMap;
 
@@ -1461,7 +1462,7 @@ mod tests {
 						tx,
 					)
 				) if pov == pov && &c == candidate_a.descriptor() => {
-					tx.send(Ok(ValidationResult::Invalid)).unwrap();
+					tx.send(Ok(ValidationResult::Invalid(InvalidCandidate::BadReturn))).unwrap();
 				}
 			);
 
@@ -1597,7 +1598,7 @@ mod tests {
 						tx,
 					)
 				) if pov == pov && &c == candidate.descriptor() => {
-					tx.send(Ok(ValidationResult::Invalid)).unwrap();
+					tx.send(Ok(ValidationResult::Invalid(InvalidCandidate::BadReturn))).unwrap();
 				}
 			);
 
@@ -1729,7 +1730,7 @@ mod tests {
 						tx,
 					)
 				) if pov == pov && &c == candidate.descriptor() => {
-					tx.send(Err(ValidationFailed)).unwrap();
+					tx.send(Err(ValidationFailed("Internal test error".into()))).unwrap();
 				}
 			);
 

node/core/candidate-validation/src/lib.rs

@@ -28,12 +28,13 @@ use polkadot_subsystem::messages::{
 	AllMessages, CandidateValidationMessage, RuntimeApiMessage, ValidationFailed, RuntimeApiRequest,
 };
 use polkadot_subsystem::errors::RuntimeApiError;
-use polkadot_node_primitives::{ValidationResult, ValidationOutputs};
+use polkadot_node_primitives::{ValidationResult, ValidationOutputs, InvalidCandidate};
 use polkadot_primitives::v1::{
 	ValidationCode, OmittedValidationData, PoV, CandidateDescriptor, LocalValidationData,
 	GlobalValidationData, OccupiedCoreAssumption, Hash, validation_data_hash,
 };
-use polkadot_parachain::wasm_executor::{self, ValidationPool, ExecutionMode};
+use polkadot_parachain::wasm_executor::{self, ValidationPool, ExecutionMode, ValidationError,
+	InvalidCandidate as WasmInvalidCandidate};
 use polkadot_parachain::primitives::{ValidationResult as WasmValidationResult, ValidationParams};
 
 use parity_scale_codec::Encode;
@@ -241,7 +242,7 @@ async fn spawn_validate_from_chain_state(
 					e,
 				);
 
-				return Ok(Err(ValidationFailed));
+				return Ok(Err(ValidationFailed("Error making API request".into())));
 			}
 		}
 	};
@@ -264,7 +265,7 @@ async fn spawn_validate_from_chain_state(
 			).await;
 		}
 		AssumptionCheckOutcome::DoesNotMatch => {},
-		AssumptionCheckOutcome::BadRequest => return Ok(Err(ValidationFailed)),
+		AssumptionCheckOutcome::BadRequest => return Ok(Err(ValidationFailed("Bad request".into()))),
 	}
 
 	match check_assumption_validation_data(
@@ -285,13 +286,13 @@ async fn spawn_validate_from_chain_state(
 			).await;
 		}
 		AssumptionCheckOutcome::DoesNotMatch => {},
-		AssumptionCheckOutcome::BadRequest => return Ok(Err(ValidationFailed)),
+		AssumptionCheckOutcome::BadRequest => return Ok(Err(ValidationFailed("Bad request".into()))),
 	}
 
 	// If neither the assumption of the occupied core having the para included or the assumption
 	// of the occupied core timing out are valid, then the validation_data_hash in the descriptor
 	// is not based on the relay parent and is thus invalid.
-	Ok(Ok(ValidationResult::Invalid))
+	Ok(Ok(ValidationResult::Invalid(InvalidCandidate::BadParent)))
 }
 
 async fn spawn_validate_exhaustive(
@@ -321,52 +322,52 @@ async fn spawn_validate_exhaustive(
 	rx.await.map_err(Into::into)
 }
 
-/// Does basic checks of a candidate. Provide the encoded PoV-block. Returns `true` if basic checks
-/// are passed, false otherwise.
-fn passes_basic_checks(
+/// Does basic checks of a candidate. Provide the encoded PoV-block. Returns `Ok` if basic checks
+/// are passed, `Err` otherwise.
+fn perform_basic_checks(
 	candidate: &CandidateDescriptor,
 	max_block_data_size: Option<u64>,
 	pov: &PoV,
-) -> bool {
+) -> Result<(), InvalidCandidate> {
 	let encoded_pov = pov.encode();
 	let hash = pov.hash();
 
 	if let Some(max_size) = max_block_data_size {
 		if encoded_pov.len() as u64 > max_size {
-			return false;
+			return Err(InvalidCandidate::ParamsTooLarge(encoded_pov.len() as u64));
 		}
 	}
 
 	if hash != candidate.pov_hash {
-		return false;
+		return Err(InvalidCandidate::HashMismatch);
 	}
 
 	if let Err(()) = candidate.check_collator_signature() {
-		return false;
+		return Err(InvalidCandidate::BadSignature);
 	}
 
-	true
+	Ok(())
 }
 
 /// Check the result of Wasm execution against the constraints given by the relay-chain.
 ///
-/// Returns `true` if checks pass, false otherwise.
+/// Returns `Ok(())` if checks pass, error otherwise.
 fn check_wasm_result_against_constraints(
 	global_validation_data: &GlobalValidationData,
 	_local_validation_data: &LocalValidationData,
 	result: &WasmValidationResult,
-) -> bool {
+) -> Result<(), InvalidCandidate> {
 	if result.head_data.0.len() > global_validation_data.max_head_data_size as _ {
-		return false
+		return Err(InvalidCandidate::HeadDataTooLarge(result.head_data.0.len() as u64))
 	}
 
 	if let Some(ref code) = result.new_validation_code {
 		if code.0.len() > global_validation_data.max_code_size as _ {
-			return false
+			return Err(InvalidCandidate::NewCodeTooLarge(code.0.len() as u64))
 		}
 	}
 
-	true
+	Ok(())
 }
 
 trait ValidationBackend {
@@ -377,7 +378,7 @@ trait ValidationBackend {
 		validation_code: &ValidationCode,
 		params: ValidationParams,
 		spawn: S,
-	) -> Result<WasmValidationResult, wasm_executor::Error>;
+	) -> Result<WasmValidationResult, ValidationError>;
 }
 
 struct RealValidationBackend;
@@ -390,7 +391,7 @@ impl ValidationBackend for RealValidationBackend {
 		validation_code: &ValidationCode,
 		params: ValidationParams,
 		spawn: S,
-	) -> Result<WasmValidationResult, wasm_executor::Error> {
+	) -> Result<WasmValidationResult, ValidationError> {
 		let execution_mode = pool.as_ref()
 			.map(ExecutionMode::Remote)
 			.unwrap_or(ExecutionMode::Local);
@@ -415,8 +416,8 @@ fn validate_candidate_exhaustive<B: ValidationBackend, S: SpawnNamed + 'static>(
 	pov: Arc<PoV>,
 	spawn: S,
 ) -> Result<ValidationResult, ValidationFailed> {
-	if !passes_basic_checks(&descriptor, None, &*pov) {
-		return Ok(ValidationResult::Invalid);
+	if let Err(e) = perform_basic_checks(&descriptor, None, &*pov) {
+		return Ok(ValidationResult::Invalid(e))
 	}
 
 	let OmittedValidationData { global_validation, local_validation } = omitted_validation;
@@ -431,26 +432,36 @@ fn validate_candidate_exhaustive<B: ValidationBackend, S: SpawnNamed + 'static>(
 	};
 
 	match B::validate(backend_arg, &validation_code, params, spawn) {
-		Err(wasm_executor::Error::BadReturn) => Ok(ValidationResult::Invalid),
-		Err(_) => Err(ValidationFailed),
+		Err(ValidationError::InvalidCandidate(WasmInvalidCandidate::Timeout)) =>
+			Ok(ValidationResult::Invalid(InvalidCandidate::Timeout)),
+		Err(ValidationError::InvalidCandidate(WasmInvalidCandidate::ParamsTooLarge(l))) =>
+			Ok(ValidationResult::Invalid(InvalidCandidate::ParamsTooLarge(l as u64))),
+		Err(ValidationError::InvalidCandidate(WasmInvalidCandidate::CodeTooLarge(l))) =>
+			Ok(ValidationResult::Invalid(InvalidCandidate::CodeTooLarge(l as u64))),
+		Err(ValidationError::InvalidCandidate(WasmInvalidCandidate::BadReturn)) =>
+			Ok(ValidationResult::Invalid(InvalidCandidate::BadReturn)),
+		Err(ValidationError::InvalidCandidate(WasmInvalidCandidate::WasmExecutor(e))) =>
+			Ok(ValidationResult::Invalid(InvalidCandidate::ExecutionError(e.to_string()))),
+		Err(ValidationError::InvalidCandidate(WasmInvalidCandidate::ExternalWasmExecutor(e))) =>
+			Ok(ValidationResult::Invalid(InvalidCandidate::ExecutionError(e.to_string()))),
+		Err(ValidationError::Internal(e)) => Err(ValidationFailed(e.to_string())),
 		Ok(res) => {
-			let passes_post_checks = check_wasm_result_against_constraints(
+			let post_check_result = check_wasm_result_against_constraints(
 				&global_validation,
 				&local_validation,
 				&res,
 			);
 
-			Ok(if passes_post_checks {
-				ValidationResult::Valid(ValidationOutputs {
+			Ok(match post_check_result {
+				Ok(()) => ValidationResult::Valid(ValidationOutputs {
 					head_data: res.head_data,
 					global_validation_data: global_validation,
 					local_validation_data: local_validation,
 					upward_messages: res.upward_messages,
 					fees: 0,
 					new_validation_code: res.new_validation_code,
-				})
-			} else {
-				ValidationResult::Invalid
+				}),
+				Err(e) => ValidationResult::Invalid(e),
 			})
 		}
 	}
@@ -469,7 +480,7 @@ mod tests {
 	struct MockValidationBackend;
 
 	struct MockValidationArg {
-		result: Result<WasmValidationResult, wasm_executor::Error>,
+		result: Result<WasmValidationResult, ValidationError>,
 	}
 
 	impl ValidationBackend for MockValidationBackend {
@@ -480,7 +491,7 @@ mod tests {
 			_validation_code: &ValidationCode,
 			_params: ValidationParams,
 			_spawn: S,
-		) -> Result<WasmValidationResult, wasm_executor::Error> {
+		) -> Result<WasmValidationResult, ValidationError> {
 			arg.result
 		}
 	}
@@ -795,7 +806,7 @@ mod tests {
 		descriptor.pov_hash = pov.hash();
 		collator_sign(&mut descriptor, Sr25519Keyring::Alice);
 
-		assert!(passes_basic_checks(&descriptor, Some(1024), &pov));
+		assert!(perform_basic_checks(&descriptor, Some(1024), &pov).is_ok());
 
 		let validation_result = WasmValidationResult {
 			head_data: HeadData(vec![1, 1, 1]),
@@ -808,7 +819,7 @@ mod tests {
 			&omitted_validation.global_validation,
 			&omitted_validation.local_validation,
 			&validation_result,
-		));
+		).is_ok());
 
 		let v = validate_candidate_exhaustive::<MockValidationBackend, _>(
 			MockValidationArg { result: Ok(validation_result) },
@@ -845,7 +856,7 @@ mod tests {
 		descriptor.pov_hash = pov.hash();
 		collator_sign(&mut descriptor, Sr25519Keyring::Alice);
 
-		assert!(passes_basic_checks(&descriptor, Some(1024), &pov));
+		assert!(perform_basic_checks(&descriptor, Some(1024), &pov).is_ok());
 
 		let validation_result = WasmValidationResult {
 			head_data: HeadData(vec![1, 1, 1]),
@@ -858,10 +869,14 @@ mod tests {
 			&omitted_validation.global_validation,
 			&omitted_validation.local_validation,
 			&validation_result,
-		));
+		).is_ok());
 
 		let v = validate_candidate_exhaustive::<MockValidationBackend, _>(
-			MockValidationArg { result: Err(wasm_executor::Error::BadReturn) },
+			MockValidationArg {
+				result: Err(ValidationError::InvalidCandidate(
+					WasmInvalidCandidate::BadReturn
+				))
+			},
 			omitted_validation.clone(),
 			vec![1, 2, 3].into(),
 			descriptor,
@@ -869,7 +884,7 @@ mod tests {
 			TaskExecutor::new(),
 		).unwrap();
 
-		assert_matches!(v, ValidationResult::Invalid);
+		assert_matches!(v, ValidationResult::Invalid(InvalidCandidate::BadReturn));
 	}
 
 
@@ -889,7 +904,7 @@ mod tests {
 		descriptor.pov_hash = pov.hash();
 		collator_sign(&mut descriptor, Sr25519Keyring::Alice);
 
-		assert!(passes_basic_checks(&descriptor, Some(1024), &pov));
+		assert!(perform_basic_checks(&descriptor, Some(1024), &pov).is_ok());
 
 		let validation_result = WasmValidationResult {
 			head_data: HeadData(vec![1, 1, 1]),
@@ -902,10 +917,14 @@ mod tests {
 			&omitted_validation.global_validation,
 			&omitted_validation.local_validation,
 			&validation_result,
-		));
+		).is_ok());
 
 		let v = validate_candidate_exhaustive::<MockValidationBackend, _>(
-			MockValidationArg { result: Err(wasm_executor::Error::Timeout) },
+			MockValidationArg {
+				result: Err(ValidationError::InvalidCandidate(
+					WasmInvalidCandidate::Timeout
+				))
+			},
 			omitted_validation.clone(),
 			vec![1, 2, 3].into(),
 			descriptor,
@@ -913,6 +932,6 @@ mod tests {
 			TaskExecutor::new(),
 		);
 
-		assert_matches!(v, Err(ValidationFailed));
+		assert_matches!(v, Ok(ValidationResult::Invalid(InvalidCandidate::Timeout)));
 	}
 }

node/primitives/src/lib.rs

@@ -129,13 +129,38 @@ pub struct ValidationOutputs {
 	pub new_validation_code: Option<ValidationCode>,
 }
 
+/// Candidate invalidity details
+#[derive(Debug)]
+pub enum InvalidCandidate {
+	/// Failed to execute.`validate_block`. This includes function panicking.
+	ExecutionError(String),
+	/// Execution timeout.
+	Timeout,
+	/// Validation input is over the limit.
+	ParamsTooLarge(u64),
+	/// Code size is over the limit.
+	CodeTooLarge(u64),
+	/// Validation function returned invalid data.
+	BadReturn,
+	/// Invalid relay chain parent.
+	BadParent,
+	/// POV hash does not match.
+	HashMismatch,
+	/// Bad collator signature.
+	BadSignature,
+	/// Output code is too large
+	NewCodeTooLarge(u64),
+	/// Head-data is over the limit.
+	HeadDataTooLarge(u64),
+}
+
 /// Result of the validation of the candidate.
 #[derive(Debug)]
 pub enum ValidationResult {
 	/// Candidate is valid. The validation process yields these outputs.
 	Valid(ValidationOutputs),
 	/// Candidate is invalid.
-	Invalid,
+	Invalid(InvalidCandidate),
 }
 
 impl std::convert::TryFrom<FromTableMisbehavior> for MisbehaviorReport {

node/subsystem/src/messages.rs

@@ -87,9 +87,9 @@ impl CandidateBackingMessage {
 	}
 }
 
-/// Blanket error for validation failing.
+/// Blanket error for validation failing for internal reasons.
 #[derive(Debug)]
-pub struct ValidationFailed;
+pub struct ValidationFailed(pub String);
 
 /// Messages received by the Validation subsystem.
 ///

parachain/src/wasm_executor/mod.rs

@@ -69,9 +69,18 @@ pub enum ExecutionMode<'a> {
 	RemoteTest(&'a ValidationPool),
 }
 
-/// Error type for the wasm executor
 #[derive(Debug, derive_more::Display, derive_more::From)]
-pub enum Error {
+/// Candidate validation error.
+pub enum ValidationError {
+	/// Validation failed due to internal reasons. The candidate might still be valid.
+	Internal(InternalError),
+	/// Candidate is invalid.
+	InvalidCandidate(InvalidCandidate),
+}
+
+/// Error type that indicates invalid candidate.
+#[derive(Debug, derive_more::Display, derive_more::From)]
+pub enum InvalidCandidate {
 	/// Wasm executor error.
 	#[display(fmt = "WASM executor error: {:?}", _0)]
 	WasmExecutor(sc_executor::error::Error),
@@ -82,30 +91,37 @@ pub enum Error {
 	/// Code size it too large.
 	#[display(fmt = "WASM code is {} bytes, max allowed is {}", _0, MAX_CODE_MEM)]
 	CodeTooLarge(usize),
-	/// Bad return data or type.
+	/// Error decoding returned data.
 	#[display(fmt = "Validation function returned invalid data.")]
 	BadReturn,
 	#[display(fmt = "Validation function timeout.")]
 	Timeout,
+	#[display(fmt = "External WASM execution error: {}", _0)]
+	ExternalWasmExecutor(String),
+}
+
+/// Host error during candidate validation. This does not indicate an invalid candidate.
+#[derive(Debug, derive_more::Display, derive_more::From)]
+pub enum InternalError {
 	#[display(fmt = "IO error: {}", _0)]
 	Io(std::io::Error),
 	#[display(fmt = "System error: {}", _0)]
 	System(Box<dyn std::error::Error + Send>),
-	#[display(fmt = "WASM worker error: {}", _0)]
-	External(String),
 	#[display(fmt = "Shared memory error: {}", _0)]
 	#[cfg(not(any(target_os = "android", target_os = "unknown")))]
 	SharedMem(shared_memory::SharedMemError),
+	#[display(fmt = "WASM worker error: {}", _0)]
+	WasmWorker(String),
 }
 
-impl std::error::Error for Error {
+impl std::error::Error for ValidationError {
 	fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
 		match self {
-			Error::WasmExecutor(ref err) => Some(err),
-			Error::Io(ref err) => Some(err),
-			Error::System(ref err) => Some(&**err),
+			ValidationError::Internal(InternalError::Io(ref err)) => Some(err),
+			ValidationError::Internal(InternalError::System(ref err)) => Some(&**err),
 			#[cfg(not(any(target_os = "android", target_os = "unknown")))]
-			Error::SharedMem(ref err) => Some(err),
+			ValidationError::Internal(InternalError::SharedMem(ref err)) => Some(err),
+			ValidationError::InvalidCandidate(InvalidCandidate::WasmExecutor(ref err)) => Some(err),
 			_ => None,
 		}
 	}
@@ -119,7 +135,7 @@ pub fn validate_candidate(
 	params: ValidationParams,
 	options: ExecutionMode<'_>,
 	spawner: impl SpawnNamed + 'static,
-) -> Result<ValidationResult, Error> {
+) -> Result<ValidationResult, ValidationError> {
 	match options {
 		ExecutionMode::Local => {
 			validate_candidate_internal(validation_code, &params.encode(), spawner)
@@ -133,15 +149,19 @@ pub fn validate_candidate(
 			pool.validate_candidate(validation_code, params, true)
 		},
 		#[cfg(any(target_os = "android", target_os = "unknown"))]
-		ExecutionMode::Remote(pool) =>
-			Err(Error::System(Box::<dyn std::error::Error + Send + Sync>::from(
-				"Remote validator not available".to_string()
-			) as Box<_>)),
+		ExecutionMode::Remote(_pool) =>
+			Err(ValidationError::Internal(InternalError::System(
+				Box::<dyn std::error::Error + Send + Sync>::from(
+					"Remote validator not available".to_string()
+				) as Box<_>
+			))),
 		#[cfg(any(target_os = "android", target_os = "unknown"))]
-		ExecutionMode::RemoteTest(pool) =>
-			Err(Error::System(Box::<dyn std::error::Error + Send + Sync>::from(
-				"Remote validator not available".to_string()
-			) as Box<_>)),
+		ExecutionMode::RemoteTest(_pool) =>
+			Err(ValidationError::Internal(InternalError::System(
+				Box::<dyn std::error::Error + Send + Sync>::from(
+					"Remote validator not available".to_string()
+				) as Box<_>
+			))),
 	}
 }
 
@@ -155,7 +175,7 @@ pub fn validate_candidate_internal(
 	validation_code: &[u8],
 	encoded_call_data: &[u8],
 	spawner: impl SpawnNamed + 'static,
-) -> Result<ValidationResult, Error> {
+) -> Result<ValidationResult, ValidationError> {
 	let mut extensions = Extensions::new();
 	extensions.register(sp_core::traits::TaskExecutorExt::new(spawner));
 
@@ -175,9 +195,10 @@ pub fn validate_candidate_internal(
 		encoded_call_data,
 		&mut ext,
 		sp_core::traits::MissingHostFunctions::Allow,
-	)?;
+	).map_err(|e| ValidationError::InvalidCandidate(e.into()))?;
 
-	ValidationResult::decode(&mut &res[..]).map_err(|_| Error::BadReturn.into())
+	ValidationResult::decode(&mut &res[..])
+		.map_err(|_| ValidationError::InvalidCandidate(InvalidCandidate::BadReturn).into())
 }
 
 /// The validation externalities that will panic on any storage related access. They just provide

parachain/src/wasm_executor/validation_host.rs

@@ -19,7 +19,8 @@
 use std::{process, env, sync::Arc, sync::atomic};
 use codec::{Decode, Encode};
 use crate::primitives::{ValidationParams, ValidationResult};
-use super::{validate_candidate_internal, Error, MAX_CODE_MEM, MAX_RUNTIME_MEM};
+use super::{validate_candidate_internal, ValidationError, InvalidCandidate, InternalError,
+			MAX_CODE_MEM, MAX_RUNTIME_MEM};
 use shared_memory::{SharedMem, SharedMemConf, EventState, WriteLockable, EventWait, EventSet};
 use parking_lot::Mutex;
 use log::{debug, trace};
@@ -88,7 +89,7 @@ impl ValidationPool {
 		validation_code: &[u8],
 		params: ValidationParams,
 		test_mode: bool,
-	) -> Result<ValidationResult, Error> {
+	) -> Result<ValidationResult, ValidationError> {
 		for host in self.hosts.iter() {
 			if let Some(mut host) = host.try_lock() {
 				return host.validate_candidate(validation_code, params, test_mode);
@@ -165,7 +166,10 @@ pub fn run_worker(mem_id: &str) -> Result<(), String> {
 
 				match result {
 					Ok(r) => ValidationResultHeader::Ok(r),
-					Err(e) => ValidationResultHeader::Error(e.to_string()),
+					Err(ValidationError::Internal(e)) =>
+						ValidationResultHeader::Error(WorkerValidationError::InternalError(e.to_string())),
+					Err(ValidationError::InvalidCandidate(e)) =>
+						ValidationResultHeader::Error(WorkerValidationError::ValidationError(e.to_string())),
 				}
 			};
 			let mut data: &mut[u8] = &mut **slice;
@@ -186,9 +190,15 @@ struct ValidationHeader {
 }
 
 #[derive(Encode, Decode, Debug)]
-pub enum ValidationResultHeader {
+enum WorkerValidationError {
+	InternalError(String),
+	ValidationError(String),
+}
+
+#[derive(Encode, Decode, Debug)]
+enum ValidationResultHeader {
 	Ok(ValidationResult),
-	Error(String),
+	Error(WorkerValidationError),
 }
 
 unsafe impl Send for ValidationHost {}
@@ -209,7 +219,7 @@ impl Drop for ValidationHost {
 }
 
 impl ValidationHost {
-	fn create_memory() -> Result<SharedMem, Error> {
+	fn create_memory() -> Result<SharedMem, InternalError> {
 		let mem_size = MAX_RUNTIME_MEM + MAX_CODE_MEM + 1024;
 		let mem_config = SharedMemConf::default()
 			.set_size(mem_size)
@@ -221,7 +231,7 @@ impl ValidationHost {
 		Ok(mem_config.create()?)
 	}
 
-	fn start_worker(&mut self, test_mode: bool) -> Result<(), Error> {
+	fn start_worker(&mut self, test_mode: bool) -> Result<(), InternalError> {
 		if let Some(ref mut worker) = self.worker {
 			// Check if still alive
 			if let Ok(None) = worker.try_wait() {
@@ -257,9 +267,9 @@ impl ValidationHost {
 		validation_code: &[u8],
 		params: ValidationParams,
 		test_mode: bool,
-	) -> Result<ValidationResult, Error> {
+	) -> Result<ValidationResult, ValidationError> {
 		if validation_code.len() > MAX_CODE_MEM {
-			return Err(Error::CodeTooLarge(validation_code.len()));
+			return Err(ValidationError::InvalidCandidate(InvalidCandidate::CodeTooLarge(validation_code.len())));
 		}
 		// First, check if need to spawn the child process
 		self.start_worker(test_mode)?;
@@ -267,7 +277,8 @@ impl ValidationHost {
 			.expect("memory is always `Some` after `start_worker` completes successfully");
 		{
 			// Put data in shared mem
-			let data: &mut[u8] = &mut **memory.wlock_as_slice(0)?;
+			let data: &mut[u8] = &mut **memory.wlock_as_slice(0)
+				.map_err(|e|ValidationError::Internal(e.into()))?;
 			let (mut header_buf, rest) = data.split_at_mut(1024);
 			let (code, rest) = rest.split_at_mut(MAX_CODE_MEM);
 			let (code, _) = code.split_at_mut(validation_code.len());
@@ -275,7 +286,7 @@ impl ValidationHost {