Clear WASM linear memory on other OSes besides Linux too (#10291)

substrate/client/executor/wasmtime/src/instance_wrapper.rs

@@ -403,10 +403,10 @@ impl InstanceWrapper {
 		self.memory.data_ptr(ctx)
 	}
 
-	/// Removes physical backing from the allocated linear memory. This leads to returning the
-	/// memory back to the system. While the memory is zeroed this is considered as a side-effect
-	/// and is not relied upon. Thus this function acts as a hint.
-	pub fn decommit(&self, ctx: impl AsContext) {
+	/// If possible removes physical backing from the allocated linear memory which
+	/// leads to returning the memory back to the system; this also zeroes the memory
+	/// as a side-effect.
+	pub fn decommit(&self, mut ctx: impl AsContextMut) {
 		if self.memory.data_size(&ctx) == 0 {
 			return
 		}
@@ -417,7 +417,7 @@ impl InstanceWrapper {
 
 				unsafe {
 					let ptr = self.memory.data_ptr(&ctx);
-					let len = self.memory.data_size(ctx);
+					let len = self.memory.data_size(&ctx);
 
 					// Linux handles MADV_DONTNEED reliably. The result is that the given area
 					// is unmapped and will be zeroed on the next pagefault.
@@ -429,9 +429,15 @@ impl InstanceWrapper {
 								std::io::Error::last_os_error(),
 							);
 						});
+					} else {
+						return;
 					}
 				}
 			}
 		}
+
+		// If we're on an unsupported OS or the memory couldn't have been
+		// decommited for some reason then just manually zero it out.
+		self.memory.data_mut(ctx.as_context_mut()).fill(0);
 	}
 }

substrate/client/executor/wasmtime/src/runtime.rs

@@ -237,7 +237,7 @@ impl WasmInstance for WasmtimeInstance {
 
 				// Signal to the OS that we are done with the linear memory and that it can be
 				// reclaimed.
-				instance_wrapper.decommit(&store);
+				instance_wrapper.decommit(store);
 
 				result
 			},
@@ -415,11 +415,7 @@ pub struct Semantics {
 	///
 	/// Primarily this is achieved by not recreating the instance for each call and performing a
 	/// bare minimum clean up: reapplying the data segments and restoring the values for global
-	/// variables. The vast majority of the linear memory is not restored, meaning that effects
-	/// of previous executions on the same [`WasmInstance`] can be observed there.
-	///
-	/// This is not a problem for a standard substrate runtime execution because it's up to the
-	/// runtime itself to make sure that it doesn't involve any non-determinism.
+	/// variables.
 	///
 	/// Since this feature depends on instrumentation, it can be set only if runtime is
 	/// instantiated using the runtime blob, e.g. using [`create_runtime`].