Integrate Wasmer into Substrate sandbox environment (#5920)

* Add comments and refactor Sandbox module * Adds some comments * Add wasmtime instance to the sandbox and delegate calls * Adds module imports stub * WIP state holder via *mut * My take at the problem * Brings back invoke and instantiate implementation details * Removes redundant bound * Code cleanup * Fixes invoke closure * Refactors FunctionExecutor to eliminate lifetime * Wraps `FunctionExecutor::sandbox_store` in `RefCell` * Renames `FunctionExecutor::heap` to `allocator` * Wraps `FunctionExecutor::allocator` in `RefCell` * Refactors FunctionExecutor to `Rc<Inner>` pattern * Implements scoped TLS for FunctionExecutor * Fixes wasmi instancing * Fixes sandbox asserts * Makes sandbox compile after wasmtime API change * Uses Vurich/wasmtime for the Lightbeam backend * Uses wasmtime instead of wasmi for sandbox API results * Refactors sandbox to use one of the execution backends at a time * Fixes wasmtime module instantiation * TEMP vurich branch stuff * Adds wasmer impl stub * Adds get global * Fixes warnings * Adds wasmer invoke impl * Implements host function interface for wasmer * Fixes wasmer instantiation result * Adds workaround to remove debug_assert * Fixes import object generation for wasmer * Attempt to propagate wasmer::Store through sandbox::Store * Wraps `sandbox::Store::memories` in `RefCell` * Moves `sandbox::instantiate` to `sandbox::Store` * Eliminate `RefCell<memories>` * Implements `HostState::memory_get/set`, removes accidental `borrow_mut` * Fixes sandbox memory handling for wasmi * Fix memory allocation * Resets Cargo.lock to match master * Fixes compilation * Refactors sandbox to use TLS for dispatch_thunk propagation to wasmer * Pass dispatch thunk to the sandbox as a TLS * Initialize dispatch thunk holder in `SandboxInstance` * Comment out Wasmtime/Lightbeam sandbox backend * Revert wasmtime back to mainstream * Adds SandboxExecutionMethod enum for cli param * Cleanup sandbox code * Allow wasmi to access wasmer memory regions * More cleanup * Remove debug logging, replace asserts with runtime errors * Revert "Adds SandboxExecutionMethod enum for cli param" This reverts commit dcb2b1d3b54145ab51ad2e3fef0d980ba215b596. * Fixes warnings * Fixes indentation and line width * Fix return types condition * Puts everything related under the `wasmer-sandbox` feature flag * Fixes warnings * Address grumbles * Split instantiate per backend * More splits * Refacmemory allocation * Nitpicks * Attempt to wrap wasmer memory in protoco enforcing type * Revert renaming * WIP wasm buffer proxy API * Reimplement util::wasmer::MemoryRef to use buffers instead of memory slices * Adds WasmiMemoryWrapper and MemoryTransfer trait * Refactor naming * Perform all memory transfers using MemoryTransfer * Adds allocating `read` * Adds comments * Removes unused imports * Removes now unused function * Pulls Cargo.lock from origin/master * Fix rustdoc * Removes unused `TransferError` * Update Cargo.lock * Removes unused import * cargo fmt * Fix feature dependency graph * Feature should flow from the top level crate * We should not assume a specific workspace structure * sc-executor-wasmi does not use the feature * sc-executor-wasmtime should not know about the feature * Fix doc typo * Enable wasmer-sandbox by default (for now) It will be removed before merge. It is so that the benchbot uses the wasmer sandbox. * cargo run --quiet --release --features=runtime-benchmarks --manifest-path=bin/node/cli/Cargo.toml -- benchmark --chain=dev --steps=50 --repeat=20 --pallet=pallet_contracts --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --output=./frame/contracts/src/weights.rs --template=./.maintain/frame-weight-template.hbs * Revert "cargo run --quiet --release --features=runtime-benchmarks --manifest-path=bin/node/cli/Cargo.toml -- benchmark --chain=dev --steps=50 --repeat=20 --pallet=pallet_contracts --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --output=./frame/contracts/src/weights.rs --template=./.maintain/frame-weight-template.hbs" This reverts commit d713590ba45387c4204b2ad97c8bd6f6ebabda4e. * cargo fmt * Add ci-check to prevent wasmer sandbox build breaking * Run tests with wasmer-sandbox enabled * Revert "Run tests with wasmer-sandbox enabled" This reverts commit cff63156a162f9ffdab23e7cb94a30f44e320f8a. Co-authored-by: Sergei Shulepov <s.pepyakin@gmail.com> Co-authored-by: Andrew Jones <ascjones@gmail.com> Co-authored-by: Alexander Theißen <alex.theissen@me.com> Co-authored-by: Parity Benchmarking Bot <admin@parity.io>
2026-04-26 09:57:56 +00:00 · 2021-08-19 20:04:13 +07:00
parent ccfe485b91
commit 61606a0b3b
15 changed files with 1669 additions and 320 deletions
@@ -18,19 +18,25 @@

 //! This module implements sandboxing support in the runtime.
 //!
-//! Sandboxing is baked by wasmi at the moment. In future, however, we would like to add/switch to
-//! a compiled execution engine.
+//! Sandboxing is backed by wasmi and wasmer, depending on the configuration.

-use crate::error::{Error, Result};
+use crate::{
+	error::{Error, Result},
+	util,
+};
 use codec::{Decode, Encode};
 use sp_core::sandbox as sandbox_primitives;
 use sp_wasm_interface::{FunctionContext, Pointer, WordSize};
 use std::{collections::HashMap, rc::Rc};
 use wasmi::{
-	memory_units::Pages, Externals, ImportResolver, MemoryInstance, MemoryRef, Module,
-	ModuleInstance, ModuleRef, RuntimeArgs, RuntimeValue, Trap, TrapKind,
+	memory_units::Pages, Externals, ImportResolver, MemoryInstance, Module, ModuleInstance,
+	RuntimeArgs, RuntimeValue, Trap, TrapKind,
 };

+#[cfg(feature = "wasmer-sandbox")]
+use crate::util::wasmer::MemoryWrapper as WasmerMemoryWrapper;
+use crate::util::wasmi::MemoryWrapper as WasmiMemoryWrapper;
+
 /// Index of a function inside the supervisor.
 ///
 /// This is a typically an index in the default table of the supervisor, however
@@ -46,34 +52,59 @@ impl From<SupervisorFuncIndex> for usize {

 /// Index of a function within guest index space.
 ///
-/// This index is supposed to be used with as index for `Externals`.
+/// This index is supposed to be used as index for `Externals`.
 #[derive(Copy, Clone, Debug, PartialEq)]
 struct GuestFuncIndex(usize);

 /// This struct holds a mapping from guest index space to supervisor.
 struct GuestToSupervisorFunctionMapping {
+	/// Position of elements in this vector are interpreted
+	/// as indices of guest functions and are mapped to
+	/// corresponding supervisor function indices.
 	funcs: Vec<SupervisorFuncIndex>,
 }

 impl GuestToSupervisorFunctionMapping {
+	/// Create an empty function mapping
 	fn new() -> GuestToSupervisorFunctionMapping {
 		GuestToSupervisorFunctionMapping { funcs: Vec::new() }
 	}

+	/// Add a new supervisor function to the mapping.
+	/// Returns a newly assigned guest function index.
 	fn define(&mut self, supervisor_func: SupervisorFuncIndex) -> GuestFuncIndex {
 		let idx = self.funcs.len();
 		self.funcs.push(supervisor_func);
 		GuestFuncIndex(idx)
 	}

+	/// Find supervisor function index by its corresponding guest function index
 	fn func_by_guest_index(&self, guest_func_idx: GuestFuncIndex) -> Option<SupervisorFuncIndex> {
 		self.funcs.get(guest_func_idx.0).cloned()
 	}
 }

+/// Holds sandbox function and memory imports and performs name resolution
 struct Imports {
+	/// Maps qualified function name to its guest function index
 	func_map: HashMap<(Vec<u8>, Vec<u8>), GuestFuncIndex>,
-	memories_map: HashMap<(Vec<u8>, Vec<u8>), MemoryRef>,
+
+	/// Maps qualified field name to its memory reference
+	memories_map: HashMap<(Vec<u8>, Vec<u8>), Memory>,
+}
+
+impl Imports {
+	fn func_by_name(&self, module_name: &str, func_name: &str) -> Option<GuestFuncIndex> {
+		self.func_map
+			.get(&(module_name.as_bytes().to_owned(), func_name.as_bytes().to_owned()))
+			.cloned()
+	}
+
+	fn memory_by_name(&self, module_name: &str, memory_name: &str) -> Option<Memory> {
+		self.memories_map
+			.get(&(module_name.as_bytes().to_owned(), memory_name.as_bytes().to_owned()))
+			.cloned()
+	}
 }

 impl ImportResolver for Imports {
@@ -83,10 +114,10 @@ impl ImportResolver for Imports {
 		field_name: &str,
 		signature: &::wasmi::Signature,
 	) -> std::result::Result<wasmi::FuncRef, wasmi::Error> {
-		let key = (module_name.as_bytes().to_owned(), field_name.as_bytes().to_owned());
-		let idx = *self.func_map.get(&key).ok_or_else(|| {
+		let idx = self.func_by_name(module_name, field_name).ok_or_else(|| {
 			wasmi::Error::Instantiation(format!("Export {}:{} not found", module_name, field_name))
 		})?;
+
 		Ok(wasmi::FuncInstance::alloc_host(signature.clone(), idx.0))
 	}

@@ -95,18 +126,22 @@ impl ImportResolver for Imports {
 		module_name: &str,
 		field_name: &str,
 		_memory_type: &::wasmi::MemoryDescriptor,
-	) -> std::result::Result<MemoryRef, wasmi::Error> {
-		let key = (module_name.as_bytes().to_vec(), field_name.as_bytes().to_vec());
-		let mem = self
-			.memories_map
-			.get(&key)
-			.ok_or_else(|| {
-				wasmi::Error::Instantiation(format!(
-					"Export {}:{} not found",
-					module_name, field_name
-				))
-			})?
-			.clone();
+	) -> std::result::Result<wasmi::MemoryRef, wasmi::Error> {
+		let mem = self.memory_by_name(module_name, field_name).ok_or_else(|| {
+			wasmi::Error::Instantiation(format!("Export {}:{} not found", module_name, field_name))
+		})?;
+
+		let wrapper = mem.as_wasmi().ok_or_else(|| {
+			wasmi::Error::Instantiation(format!(
+				"Unsupported non-wasmi export {}:{}",
+				module_name, field_name
+			))
+		})?;
+
+		// Here we use inner memory reference only to resolve
+		// the imports without accessing the memory contents.
+		let mem = unsafe { wrapper.clone_inner() };
+
 		Ok(mem)
 	}

@@ -134,6 +169,7 @@ impl ImportResolver for Imports {
 /// Note that this functions are only called in the `supervisor` context.
 pub trait SandboxCapabilities: FunctionContext {
 	/// Represents a function reference into the supervisor environment.
+	/// Provides an abstraction over execution environment.
 	type SupervisorFuncRef;

 	/// Invoke a function in the supervisor environment.
@@ -141,9 +177,9 @@ pub trait SandboxCapabilities: FunctionContext {
 	/// This first invokes the dispatch_thunk function, passing in the function index of the
 	/// desired function to call and serialized arguments. The thunk calls the desired function
 	/// with the deserialized arguments, then serializes the result into memory and returns
-	/// reference. The pointer to and length of the result in linear memory is encoded into an i64,
-	/// with the upper 32 bits representing the pointer and the lower 32 bits representing the
-	/// length.
+	/// reference. The pointer to and length of the result in linear memory is encoded into an
+	/// `i64`, with the upper 32 bits representing the pointer and the lower 32 bits representing
+	/// the length.
 	///
 	/// # Errors
 	///
@@ -164,11 +200,17 @@ pub trait SandboxCapabilities: FunctionContext {
 ///
 /// [`Externals`]: ../wasmi/trait.Externals.html
 pub struct GuestExternals<'a, FE: SandboxCapabilities + 'a> {
+	/// Supervisor function environment
 	supervisor_externals: &'a mut FE,
+
+	/// Instance of sandboxed module to be dispatched
 	sandbox_instance: &'a SandboxInstance<FE::SupervisorFuncRef>,
+
+	/// External state passed to guest environment, see the `instantiate` function
 	state: u32,
 }

+/// Construct trap error from specified message
 fn trap(msg: &'static str) -> Trap {
 	TrapKind::Host(Box::new(Error::Other(msg.into()))).into()
 }
@@ -199,14 +241,15 @@ impl<'a, FE: SandboxCapabilities + 'a> Externals for GuestExternals<'a, FE> {
 		// Make `index` typesafe again.
 		let index = GuestFuncIndex(index);

+		// Convert function index from guest to supervisor space
 		let func_idx = self.sandbox_instance
 			.guest_to_supervisor_mapping
 			.func_by_guest_index(index)
 			.expect(
 				"`invoke_index` is called with indexes registered via `FuncInstance::alloc_host`;
-					`FuncInstance::alloc_host` is called with indexes that was obtained from `guest_to_supervisor_mapping`;
-					`func_by_guest_index` called with `index` can't return `None`;
-					qed"
+				`FuncInstance::alloc_host` is called with indexes that were obtained from `guest_to_supervisor_mapping`;
+				`func_by_guest_index` called with `index` can't return `None`;
+				qed"
 			);

 		// Serialize arguments into a byte vector.
@@ -220,7 +263,7 @@ impl<'a, FE: SandboxCapabilities + 'a> Externals for GuestExternals<'a, FE> {

 		let state = self.state;

-		// Move serialized arguments inside the memory and invoke dispatch thunk and
+		// Move serialized arguments inside the memory, invoke dispatch thunk and
 		// then free allocated memory.
 		let invoke_args_len = invoke_args_data.len() as WordSize;
 		let invoke_args_ptr = self
@@ -299,6 +342,16 @@ where
 	f(&mut guest_externals)
 }

+/// Module instance in terms of selected backend
+enum BackendInstance {
+	/// Wasmi module instance
+	Wasmi(wasmi::ModuleRef),
+
+	/// Wasmer module instance
+	#[cfg(feature = "wasmer-sandbox")]
+	Wasmer(wasmer::Instance),
+}
+
 /// Sandboxed instance of a wasm module.
 ///
 /// It's primary purpose is to [`invoke`] exported functions on it.
@@ -314,7 +367,7 @@ where
 ///
 /// [`invoke`]: #method.invoke
 pub struct SandboxInstance<FR> {
-	instance: ModuleRef,
+	backend_instance: BackendInstance,
 	dispatch_thunk: FR,
 	guest_to_supervisor_mapping: GuestToSupervisorFunctionMapping,
 }
@@ -327,15 +380,78 @@ impl<FR> SandboxInstance<FR> {
 	///
 	/// The `state` parameter can be used to provide custom data for
 	/// these syscall implementations.
-	pub fn invoke<FE: SandboxCapabilities<SupervisorFuncRef = FR>>(
+	pub fn invoke<'a, FE, SCH, DTH>(
 		&self,
+
+		// function to call that is exported from the module
 		export_name: &str,
+
+		// arguments passed to the function
 		args: &[RuntimeValue],
-		supervisor_externals: &mut FE,
+
+		// arbitraty context data of the call
 		state: u32,
-	) -> std::result::Result<Option<wasmi::RuntimeValue>, wasmi::Error> {
-		with_guest_externals(supervisor_externals, self, state, |guest_externals| {
-			self.instance.invoke_export(export_name, args, guest_externals)
+	) -> std::result::Result<Option<wasmi::RuntimeValue>, wasmi::Error>
+	where
+		FE: SandboxCapabilities<SupervisorFuncRef = FR> + 'a,
+		SCH: SandboxCapabilitiesHolder<SupervisorFuncRef = FR, SC = FE>,
+		DTH: DispatchThunkHolder<DispatchThunk = FR>,
+	{
+		SCH::with_sandbox_capabilities(|supervisor_externals| {
+			with_guest_externals(supervisor_externals, self, state, |guest_externals| {
+				match &self.backend_instance {
+					BackendInstance::Wasmi(wasmi_instance) => {
+						let wasmi_result =
+							wasmi_instance.invoke_export(export_name, args, guest_externals)?;
+
+						Ok(wasmi_result)
+					},
+
+					#[cfg(feature = "wasmer-sandbox")]
+					BackendInstance::Wasmer(wasmer_instance) => {
+						let function = wasmer_instance
+							.exports
+							.get_function(export_name)
+							.map_err(|error| wasmi::Error::Function(error.to_string()))?;
+
+						let args: Vec<wasmer::Val> = args
+							.iter()
+							.map(|v| match *v {
+								RuntimeValue::I32(val) => wasmer::Val::I32(val),
+								RuntimeValue::I64(val) => wasmer::Val::I64(val),
+								RuntimeValue::F32(val) => wasmer::Val::F32(val.into()),
+								RuntimeValue::F64(val) => wasmer::Val::F64(val.into()),
+							})
+							.collect();
+
+						let wasmer_result =
+							DTH::initialize_thunk(&self.dispatch_thunk, || function.call(&args))
+								.map_err(|error| wasmi::Error::Function(error.to_string()))?;
+
+						if wasmer_result.len() > 1 {
+							return Err(wasmi::Error::Function(
+								"multiple return types are not supported yet".to_owned(),
+							))
+						}
+
+						let wasmer_result = if let Some(wasmer_value) = wasmer_result.first() {
+							let wasmer_value = match *wasmer_value {
+								wasmer::Val::I32(val) => RuntimeValue::I32(val),
+								wasmer::Val::I64(val) => RuntimeValue::I64(val),
+								wasmer::Val::F32(val) => RuntimeValue::F32(val.into()),
+								wasmer::Val::F64(val) => RuntimeValue::F64(val.into()),
+								_ => unreachable!(),
+							};
+
+							Some(wasmer_value)
+						} else {
+							None
+						};
+
+						Ok(wasmer_result)
+					},
+				}
+			})
 		})
 	}

@@ -343,9 +459,29 @@ impl<FR> SandboxInstance<FR> {
 	///
 	/// Returns `Some(_)` if the global could be found.
 	pub fn get_global_val(&self, name: &str) -> Option<sp_wasm_interface::Value> {
-		let global = self.instance.export_by_name(name)?.as_global()?.get();
+		match &self.backend_instance {
+			BackendInstance::Wasmi(wasmi_instance) => {
+				let wasmi_global = wasmi_instance.export_by_name(name)?.as_global()?.get();

-		Some(global.into())
+				Some(wasmi_global.into())
+			},
+
+			#[cfg(feature = "wasmer-sandbox")]
+			BackendInstance::Wasmer(wasmer_instance) => {
+				use sp_wasm_interface::Value;
+
+				let global = wasmer_instance.exports.get_global(name).ok()?;
+				let wasmtime_value = match global.get() {
+					wasmer::Val::I32(val) => Value::I32(val),
+					wasmer::Val::I64(val) => Value::I64(val),
+					wasmer::Val::F32(val) => Value::F32(f32::to_bits(val)),
+					wasmer::Val::F64(val) => Value::F64(f64::to_bits(val)),
+					_ => None?,
+				};
+
+				Some(wasmtime_value)
+			},
+		}
 	}
 }

@@ -366,7 +502,7 @@ pub enum InstantiationError {

 fn decode_environment_definition(
 	mut raw_env_def: &[u8],
-	memories: &[Option<MemoryRef>],
+	memories: &[Option<Memory>],
 ) -> std::result::Result<(Imports, GuestToSupervisorFunctionMapping), InstantiationError> {
 	let env_def = sandbox_primitives::EnvironmentDefinition::decode(&mut raw_env_def)
 		.map_err(|_| InstantiationError::EnvironmentDefinitionCorrupted)?;
@@ -401,7 +537,10 @@ fn decode_environment_definition(

 /// An environment in which the guest module is instantiated.
 pub struct GuestEnvironment {
+	/// Function and memory imports of the guest module
 	imports: Imports,
+
+	/// Supervisor functinons mapped to guest index space
 	guest_to_supervisor_mapping: GuestToSupervisorFunctionMapping,
 }

@@ -436,47 +575,142 @@ impl<FR> UnregisteredInstance<FR> {
 	}
 }

-/// Instantiate a guest module and return it's index in the store.
-///
-/// The guest module's code is specified in `wasm`. Environment that will be available to
-/// guest module is specified in `raw_env_def` (serialized version of [`EnvironmentDefinition`]).
-/// `dispatch_thunk` is used as function that handle calls from guests.
-///
-/// # Errors
-///
-/// Returns `Err` if any of the following conditions happens:
-///
-/// - `raw_env_def` can't be deserialized as a [`EnvironmentDefinition`].
-/// - Module in `wasm` is invalid or couldn't be instantiated.
-///
-/// [`EnvironmentDefinition`]: ../sandbox/struct.EnvironmentDefinition.html
-pub fn instantiate<'a, FE: SandboxCapabilities>(
-	supervisor_externals: &mut FE,
-	dispatch_thunk: FE::SupervisorFuncRef,
-	wasm: &[u8],
-	host_env: GuestEnvironment,
-	state: u32,
-) -> std::result::Result<UnregisteredInstance<FE::SupervisorFuncRef>, InstantiationError> {
-	let module = Module::from_buffer(wasm).map_err(|_| InstantiationError::ModuleDecoding)?;
-	let instance = ModuleInstance::new(&module, &host_env.imports)
-		.map_err(|_| InstantiationError::Instantiation)?;
+/// Helper type to provide sandbox capabilities to the inner context
+pub trait SandboxCapabilitiesHolder {
+	/// Supervisor function reference
+	type SupervisorFuncRef;

-	let sandbox_instance = Rc::new(SandboxInstance {
-		// In general, it's not a very good idea to use `.not_started_instance()` for anything
-		// but for extracting memory and tables. But in this particular case, we are extracting
-		// for the purpose of running `start` function which should be ok.
-		instance: instance.not_started_instance().clone(),
-		dispatch_thunk,
-		guest_to_supervisor_mapping: host_env.guest_to_supervisor_mapping,
-	});
+	/// Capabilities trait
+	type SC: SandboxCapabilities<SupervisorFuncRef = Self::SupervisorFuncRef>;

-	with_guest_externals(supervisor_externals, &sandbox_instance, state, |guest_externals| {
-		instance
-			.run_start(guest_externals)
-			.map_err(|_| InstantiationError::StartTrapped)
-	})?;
+	/// Wrapper that provides sandbox capabilities in a limited context
+	fn with_sandbox_capabilities<R, F: FnOnce(&mut Self::SC) -> R>(f: F) -> R;
+}

-	Ok(UnregisteredInstance { sandbox_instance })
+/// Helper type to provide dispatch thunk to the inner context
+pub trait DispatchThunkHolder {
+	/// Dispatch thunk for this particular context
+	type DispatchThunk;
+
+	/// Provide `DispatchThunk` for the runtime method call and execute the given function `f`.
+	///
+	/// During the execution of the provided function `dispatch_thunk` will be callable.
+	fn initialize_thunk<R, F>(s: &Self::DispatchThunk, f: F) -> R
+	where
+		F: FnOnce() -> R;
+
+	/// Wrapper that provides dispatch thunk in a limited context
+	fn with_dispatch_thunk<R, F: FnOnce(&mut Self::DispatchThunk) -> R>(f: F) -> R;
+}
+
+/// Sandbox backend to use
+pub enum SandboxBackend {
+	/// Wasm interpreter
+	Wasmi,
+
+	/// Wasmer environment
+	#[cfg(feature = "wasmer-sandbox")]
+	Wasmer,
+
+	/// Use wasmer backend if available. Fall back to wasmi otherwise.
+	TryWasmer,
+}
+
+/// Memory reference in terms of a selected backend
+#[derive(Clone, Debug)]
+pub enum Memory {
+	/// Wasmi memory reference
+	Wasmi(WasmiMemoryWrapper),
+
+	/// Wasmer memory refernce
+	#[cfg(feature = "wasmer-sandbox")]
+	Wasmer(WasmerMemoryWrapper),
+}
+
+impl Memory {
+	/// View as wasmi memory
+	pub fn as_wasmi(&self) -> Option<WasmiMemoryWrapper> {
+		match self {
+			Memory::Wasmi(memory) => Some(memory.clone()),
+
+			#[cfg(feature = "wasmer-sandbox")]
+			Memory::Wasmer(_) => None,
+		}
+	}
+
+	/// View as wasmer memory
+	#[cfg(feature = "wasmer-sandbox")]
+	pub fn as_wasmer(&self) -> Option<WasmerMemoryWrapper> {
+		match self {
+			Memory::Wasmer(memory) => Some(memory.clone()),
+			Memory::Wasmi(_) => None,
+		}
+	}
+}
+
+impl util::MemoryTransfer for Memory {
+	fn read(&self, source_addr: Pointer<u8>, size: usize) -> Result<Vec<u8>> {
+		match self {
+			Memory::Wasmi(sandboxed_memory) => sandboxed_memory.read(source_addr, size),
+
+			#[cfg(feature = "wasmer-sandbox")]
+			Memory::Wasmer(sandboxed_memory) => sandboxed_memory.read(source_addr, size),
+		}
+	}
+
+	fn read_into(&self, source_addr: Pointer<u8>, destination: &mut [u8]) -> Result<()> {
+		match self {
+			Memory::Wasmi(sandboxed_memory) => sandboxed_memory.read_into(source_addr, destination),
+
+			#[cfg(feature = "wasmer-sandbox")]
+			Memory::Wasmer(sandboxed_memory) => sandboxed_memory.read_into(source_addr, destination),
+		}
+	}
+
+	fn write_from(&self, dest_addr: Pointer<u8>, source: &[u8]) -> Result<()> {
+		match self {
+			Memory::Wasmi(sandboxed_memory) => sandboxed_memory.write_from(dest_addr, source),
+
+			#[cfg(feature = "wasmer-sandbox")]
+			Memory::Wasmer(sandboxed_memory) => sandboxed_memory.write_from(dest_addr, source),
+		}
+	}
+}
+
+/// Wasmer specific context
+#[cfg(feature = "wasmer-sandbox")]
+struct WasmerBackend {
+	store: wasmer::Store,
+}
+
+/// Information specific to a particular execution backend
+enum BackendContext {
+	/// Wasmi specific context
+	Wasmi,
+
+	/// Wasmer specific context
+	#[cfg(feature = "wasmer-sandbox")]
+	Wasmer(WasmerBackend),
+}
+
+impl BackendContext {
+	pub fn new(backend: SandboxBackend) -> BackendContext {
+		match backend {
+			SandboxBackend::Wasmi => BackendContext::Wasmi,
+
+			#[cfg(not(feature = "wasmer-sandbox"))]
+			SandboxBackend::TryWasmer => BackendContext::Wasmi,
+
+			#[cfg(feature = "wasmer-sandbox")]
+			SandboxBackend::Wasmer | SandboxBackend::TryWasmer => {
+				let compiler = wasmer_compiler_singlepass::Singlepass::default();
+
+				BackendContext::Wasmer(WasmerBackend {
+					store: wasmer::Store::new(&wasmer::JIT::new(compiler).engine()),
+				})
+			},
+		}
+	}
 }

 /// This struct keeps track of all sandboxed components.
@@ -485,13 +719,18 @@ pub fn instantiate<'a, FE: SandboxCapabilities>(
 pub struct Store<FR> {
 	// Memories and instances are `Some` until torn down.
 	instances: Vec<Option<Rc<SandboxInstance<FR>>>>,
-	memories: Vec<Option<MemoryRef>>,
+	memories: Vec<Option<Memory>>,
+	backend_context: BackendContext,
 }

 impl<FR> Store<FR> {
 	/// Create a new empty sandbox store.
-	pub fn new() -> Self {
-		Store { instances: Vec::new(), memories: Vec::new() }
+	pub fn new(backend: SandboxBackend) -> Self {
+		Store {
+			instances: Vec::new(),
+			memories: Vec::new(),
+			backend_context: BackendContext::new(backend),
+		}
 	}

 	/// Create a new memory instance and return it's index.
@@ -501,15 +740,33 @@ impl<FR> Store<FR> {
 	/// Returns `Err` if the memory couldn't be created.
 	/// Typically happens if `initial` is more than `maximum`.
 	pub fn new_memory(&mut self, initial: u32, maximum: u32) -> Result<u32> {
+		let memories = &mut self.memories;
+		let backend_context = &self.backend_context;
+
 		let maximum = match maximum {
 			sandbox_primitives::MEM_UNLIMITED => None,
-			specified_limit => Some(Pages(specified_limit as usize)),
+			specified_limit => Some(specified_limit),
 		};

-		let mem = MemoryInstance::alloc(Pages(initial as usize), maximum)?;
+		let memory = match &backend_context {
+			BackendContext::Wasmi => Memory::Wasmi(WasmiMemoryWrapper::new(MemoryInstance::alloc(
+				Pages(initial as usize),
+				maximum.map(|m| Pages(m as usize)),
+			)?)),
+
+			#[cfg(feature = "wasmer-sandbox")]
+			BackendContext::Wasmer(context) => {
+				let ty = wasmer::MemoryType::new(initial, maximum, false);
+				Memory::Wasmer(WasmerMemoryWrapper::new(
+					wasmer::Memory::new(&context.store, ty)
+						.map_err(|_| Error::InvalidMemoryReference)?,
+				))
+			},
+		};
+
+		let mem_idx = memories.len();
+		memories.push(Some(memory.clone()));

-		let mem_idx = self.memories.len();
-		self.memories.push(Some(mem));
 		Ok(mem_idx as u32)
 	}

@@ -533,7 +790,7 @@ impl<FR> Store<FR> {
 	///
 	/// Returns `Err` If `memory_idx` isn't a valid index of an memory or
 	/// if memory has been torn down.
-	pub fn memory(&self, memory_idx: u32) -> Result<MemoryRef> {
+	pub fn memory(&self, memory_idx: u32) -> Result<Memory> {
 		self.memories
 			.get(memory_idx as usize)
 			.cloned()
@@ -575,9 +832,307 @@ impl<FR> Store<FR> {
 		}
 	}

+	/// Instantiate a guest module and return it's index in the store.
+	///
+	/// The guest module's code is specified in `wasm`. Environment that will be available to
+	/// guest module is specified in `guest_env`. A dispatch thunk is used as function that
+	/// handle calls from guests. `state` is an opaque pointer to caller's arbitrary context
+	/// normally created by `sp_sandbox::Instance` primitive.
+	///
+	/// Note: Due to borrowing constraints dispatch thunk is now propagated using DTH
+	///
+	/// Returns uninitialized sandboxed module instance or an instantiation error.
+	pub fn instantiate<'a, FE, SCH, DTH>(
+		&mut self,
+		wasm: &[u8],
+		guest_env: GuestEnvironment,
+		state: u32,
+	) -> std::result::Result<UnregisteredInstance<FR>, InstantiationError>
+	where
+		FR: Clone + 'static,
+		FE: SandboxCapabilities<SupervisorFuncRef = FR> + 'a,
+		SCH: SandboxCapabilitiesHolder<SupervisorFuncRef = FR, SC = FE>,
+		DTH: DispatchThunkHolder<DispatchThunk = FR>,
+	{
+		let backend_context = &self.backend_context;
+
+		let sandbox_instance = match backend_context {
+			BackendContext::Wasmi =>
+				Self::instantiate_wasmi::<FE, SCH, DTH>(wasm, guest_env, state)?,
+
+			#[cfg(feature = "wasmer-sandbox")]
+			BackendContext::Wasmer(context) =>
+				Self::instantiate_wasmer::<FE, SCH, DTH>(context, wasm, guest_env, state)?,
+		};
+
+		Ok(UnregisteredInstance { sandbox_instance })
+	}
+}
+
+// Private routines
+impl<FR> Store<FR> {
 	fn register_sandbox_instance(&mut self, sandbox_instance: Rc<SandboxInstance<FR>>) -> u32 {
 		let instance_idx = self.instances.len();
 		self.instances.push(Some(sandbox_instance));
 		instance_idx as u32
 	}
+
+	fn instantiate_wasmi<'a, FE, SCH, DTH>(
+		wasm: &[u8],
+		guest_env: GuestEnvironment,
+		state: u32,
+	) -> std::result::Result<Rc<SandboxInstance<FR>>, InstantiationError>
+	where
+		FR: Clone + 'static,
+		FE: SandboxCapabilities<SupervisorFuncRef = FR> + 'a,
+		SCH: SandboxCapabilitiesHolder<SupervisorFuncRef = FR, SC = FE>,
+		DTH: DispatchThunkHolder<DispatchThunk = FR>,
+	{
+		let wasmi_module =
+			Module::from_buffer(wasm).map_err(|_| InstantiationError::ModuleDecoding)?;
+		let wasmi_instance = ModuleInstance::new(&wasmi_module, &guest_env.imports)
+			.map_err(|_| InstantiationError::Instantiation)?;
+
+		let sandbox_instance = DTH::with_dispatch_thunk(|dispatch_thunk| {
+			Rc::new(SandboxInstance {
+				// In general, it's not a very good idea to use `.not_started_instance()` for
+				// anything but for extracting memory and tables. But in this particular case, we
+				// are extracting for the purpose of running `start` function which should be ok.
+				backend_instance: BackendInstance::Wasmi(
+					wasmi_instance.not_started_instance().clone(),
+				),
+				dispatch_thunk: dispatch_thunk.clone(),
+				guest_to_supervisor_mapping: guest_env.guest_to_supervisor_mapping,
+			})
+		});
+
+		SCH::with_sandbox_capabilities(|supervisor_externals| {
+			with_guest_externals(
+				supervisor_externals,
+				&sandbox_instance,
+				state,
+				|guest_externals| {
+					wasmi_instance
+						.run_start(guest_externals)
+						.map_err(|_| InstantiationError::StartTrapped)
+
+					// Note: no need to run start on wasmtime instance, since it's done
+					// automatically
+				},
+			)
+		})?;
+
+		Ok(sandbox_instance)
+	}
+
+	#[cfg(feature = "wasmer-sandbox")]
+	fn instantiate_wasmer<'a, FE, SCH, DTH>(
+		context: &WasmerBackend,
+		wasm: &[u8],
+		guest_env: GuestEnvironment,
+		state: u32,
+	) -> std::result::Result<Rc<SandboxInstance<FR>>, InstantiationError>
+	where
+		FR: Clone + 'static,
+		FE: SandboxCapabilities<SupervisorFuncRef = FR> + 'a,
+		SCH: SandboxCapabilitiesHolder<SupervisorFuncRef = FR, SC = FE>,
+		DTH: DispatchThunkHolder<DispatchThunk = FR>,
+	{
+		let module = wasmer::Module::new(&context.store, wasm)
+			.map_err(|_| InstantiationError::ModuleDecoding)?;
+
+		type Exports = HashMap<String, wasmer::Exports>;
+		let mut exports_map = Exports::new();
+
+		for import in module.imports().into_iter() {
+			match import.ty() {
+				// Nothing to do here
+				wasmer::ExternType::Global(_) | wasmer::ExternType::Table(_) => (),
+
+				wasmer::ExternType::Memory(_) => {
+					let exports = exports_map
+						.entry(import.module().to_string())
+						.or_insert(wasmer::Exports::new());
+
+					let memory = guest_env
+						.imports
+						.memory_by_name(import.module(), import.name())
+						.ok_or(InstantiationError::ModuleDecoding)?;
+
+					let mut wasmer_memory_ref = memory.as_wasmer().expect(
+						"memory is created by wasmer; \
+						exported by the same module and backend; \
+						thus the operation can't fail; \
+						qed",
+					);
+
+					// This is safe since we're only instantiating the module and populating
+					// the export table, so no memory access can happen at this time.
+					// All subsequent memory accesses should happen through the wrapper,
+					// that enforces the memory access protocol.
+					let wasmer_memory = unsafe { wasmer_memory_ref.clone_inner() };
+
+					exports.insert(import.name(), wasmer::Extern::Memory(wasmer_memory));
+				},
+
+				wasmer::ExternType::Function(func_ty) => {
+					let guest_func_index =
+						guest_env.imports.func_by_name(import.module(), import.name());
+
+					let guest_func_index = if let Some(index) = guest_func_index {
+						index
+					} else {
+						// Missing import (should we abort here?)
+						continue
+					};
+
+					let supervisor_func_index = guest_env
+						.guest_to_supervisor_mapping
+						.func_by_guest_index(guest_func_index)
+						.ok_or(InstantiationError::ModuleDecoding)?;
+
+					let function = Self::wasmer_dispatch_function::<FE, SCH, DTH>(
+						supervisor_func_index,
+						&context.store,
+						func_ty,
+						state,
+					);
+
+					let exports = exports_map
+						.entry(import.module().to_string())
+						.or_insert(wasmer::Exports::new());
+
+					exports.insert(import.name(), wasmer::Extern::Function(function));
+				},
+			}
+		}
+
+		let mut import_object = wasmer::ImportObject::new();
+		for (module_name, exports) in exports_map.into_iter() {
+			import_object.register(module_name, exports);
+		}
+
+		let instance =
+			wasmer::Instance::new(&module, &import_object).map_err(|error| match error {
+				wasmer::InstantiationError::Link(_) => InstantiationError::Instantiation,
+				wasmer::InstantiationError::Start(_) => InstantiationError::StartTrapped,
+				wasmer::InstantiationError::HostEnvInitialization(_) =>
+					InstantiationError::EnvironmentDefinitionCorrupted,
+			})?;
+
+		Ok(Rc::new(SandboxInstance {
+			backend_instance: BackendInstance::Wasmer(instance),
+			dispatch_thunk: DTH::with_dispatch_thunk(|dispatch_thunk| dispatch_thunk.clone()),
+			guest_to_supervisor_mapping: guest_env.guest_to_supervisor_mapping,
+		}))
+	}
+
+	#[cfg(feature = "wasmer-sandbox")]
+	fn wasmer_dispatch_function<'a, FE, SCH, DTH>(
+		supervisor_func_index: SupervisorFuncIndex,
+		store: &wasmer::Store,
+		func_ty: &wasmer::FunctionType,
+		state: u32,
+	) -> wasmer::Function
+	where
+		FR: Clone + 'static,
+		FE: SandboxCapabilities<SupervisorFuncRef = FR> + 'a,
+		SCH: SandboxCapabilitiesHolder<SupervisorFuncRef = FR, SC = FE>,
+		DTH: DispatchThunkHolder<DispatchThunk = FR>,
+	{
+		wasmer::Function::new(store, func_ty, move |params| {
+			SCH::with_sandbox_capabilities(|supervisor_externals| {
+				use sp_wasm_interface::Value;
+
+				// Serialize arguments into a byte vector.
+				let invoke_args_data = params
+					.iter()
+					.map(|val| match val {
+						wasmer::Val::I32(val) => Value::I32(*val),
+						wasmer::Val::I64(val) => Value::I64(*val),
+						wasmer::Val::F32(val) => Value::F32(f32::to_bits(*val)),
+						wasmer::Val::F64(val) => Value::F64(f64::to_bits(*val)),
+						_ => unimplemented!(),
+					})
+					.collect::<Vec<_>>()
+					.encode();
+
+				// Move serialized arguments inside the memory, invoke dispatch thunk and
+				// then free allocated memory.
+				let invoke_args_len = invoke_args_data.len() as WordSize;
+				let invoke_args_ptr =
+					supervisor_externals.allocate_memory(invoke_args_len).map_err(|_| {
+						wasmer::RuntimeError::new(
+							"Can't allocate memory in supervisor for the arguments",
+						)
+					})?;
+
+				let deallocate = |fe: &mut FE, ptr, fail_msg| {
+					fe.deallocate_memory(ptr).map_err(|_| wasmer::RuntimeError::new(fail_msg))
+				};
+
+				if supervisor_externals.write_memory(invoke_args_ptr, &invoke_args_data).is_err() {
+					deallocate(
+						supervisor_externals,
+						invoke_args_ptr,
+						"Failed dealloction after failed write of invoke arguments",
+					)?;
+
+					return Err(wasmer::RuntimeError::new("Can't write invoke args into memory"))
+				}
+
+				// Perform the actuall call
+				let serialized_result = DTH::with_dispatch_thunk(|dispatch_thunk| {
+					supervisor_externals.invoke(
+						&dispatch_thunk,
+						invoke_args_ptr,
+						invoke_args_len,
+						state,
+						supervisor_func_index,
+					)
+				})
+				.map_err(|e| wasmer::RuntimeError::new(e.to_string()))?;
+
+				// dispatch_thunk returns pointer to serialized arguments.
+				// Unpack pointer and len of the serialized result data.
+				let (serialized_result_val_ptr, serialized_result_val_len) = {
+					// Cast to u64 to use zero-extension.
+					let v = serialized_result as u64;
+					let ptr = (v as u64 >> 32) as u32;
+					let len = (v & 0xFFFFFFFF) as u32;
+					(Pointer::new(ptr), len)
+				};
+
+				let serialized_result_val = supervisor_externals
+					.read_memory(serialized_result_val_ptr, serialized_result_val_len)
+					.map_err(|_| {
+						wasmer::RuntimeError::new(
+							"Can't read the serialized result from dispatch thunk",
+						)
+					});
+
+				let deserialized_result = deallocate(
+					supervisor_externals,
+					serialized_result_val_ptr,
+					"Can't deallocate memory for dispatch thunk's result",
+				)
+				.and_then(|_| serialized_result_val)
+				.and_then(|serialized_result_val| {
+					deserialize_result(&serialized_result_val)
+						.map_err(|e| wasmer::RuntimeError::new(e.to_string()))
+				})?;
+
+				if let Some(value) = deserialized_result {
+					Ok(vec![match value {
+						RuntimeValue::I32(val) => wasmer::Val::I32(val),
+						RuntimeValue::I64(val) => wasmer::Val::I64(val),
+						RuntimeValue::F32(val) => wasmer::Val::F32(val.into()),
+						RuntimeValue::F64(val) => wasmer::Val::F64(val.into()),
+					}])
+				} else {
+					Ok(vec![])
+				}
+			})
+		})
+	}
 }