worker: implement vm.moveMessagePortToContext()

This should help a lot with actual sandboxing of JS code.

Thanks to Timothy Gu, Stephen Belanger and Benjamin Gruenbaum
for reviewing this change in its original form.

Refs: ayojs/ayo#111

doc/api/vm.md

@@ -732,6 +732,49 @@ console.log(util.inspect(sandbox));
 // { globalVar: 1024 }
 ```
 
+## vm.moveMessagePortToContext(port, contextifiedSandbox)
+<!-- YAML
+added: REPLACEME
+-->
+
+* `port` {MessagePort}
+* `contextifiedSandbox` {Object} A contextified object as returned by the
+  `vm.createContext()` method.
+* Returns: {MessagePort}
+
+Bind a `MessagePort` to a specific VM context. This returns a new `MessagePort`
+object, whose prototype and methods act as if they were created in the passed
+context. The received messages will also be emitted as objects from the passed
+context.
+
+The `port` object on which this method was called can not be used for sending
+or receiving further messages.
+
+## vm.runInDebugContext(code)
+<!-- YAML
+added: v0.11.14
+-->
+
+> Stability: 0 - Deprecated. An alternative is in development.
+
+* `code` {string} The JavaScript code to compile and run.
+
+The `vm.runInDebugContext()` method compiles and executes `code` inside the V8
+debug context. The primary use case is to gain access to the V8 `Debug` object:
+
+```js
+const vm = require('vm');
+const Debug = vm.runInDebugContext('Debug');
+console.log(Debug.findScript(process.emit).name);  // 'events.js'
+console.log(Debug.findScript(process.exit).name);  // 'internal/process.js'
+```
+
+*Note*: The debug context and object are intrinsically tied to V8's debugger
+implementation and may change (or even be removed) without prior warning.
+
+The `Debug` object can also be made available using the V8-specific
+`--expose_debug_as=` [command line option][].
+
 ## vm.runInNewContext(code[, sandbox][, options])
 <!-- YAML
 added: v0.3.1

doc/api/worker.md

@@ -154,7 +154,10 @@ added: REPLACEME
 Instances of the `worker.MessagePort` class represent one end of an
 asynchronous, two-way communications channel. It can be used to transfer
 structured data, memory regions and other `MessagePort`s between different
-[`Worker`][]s.
+[`Worker`][]s or [`vm` context][vm]s.
+
+For transferring `MessagePort` instances between VM contexts, see
+[`vm.moveMessagePortToContext()`][].
 
 *Note*: With the exception of `MessagePort`s being [`EventEmitter`][]s rather
 than `EventTarget`s, this implementation matches [browser `MessagePort`][]s.
@@ -260,7 +263,9 @@ added: REPLACEME
 
 Starts receiving messages on this `MessagePort`. When using this port
 as an event emitter, this will be called automatically once `'message'`
-listeners are attached.
+listeners are attached. This means that this method does not need to be used
+unless you are using [`vm.moveMessagePortToContext()`][] to move this `port`
+into another VM context.
 
 ## Class: Worker
 <!-- YAML
@@ -449,6 +454,8 @@ it is available as [`require('worker').threadId`][].
 [`require('worker').postMessage()`]: #worker_worker_postmessage_value_transferlist
 [`require('worker').isMainThread`]: #worker_worker_is_main_thread
 [`require('worker').threadId`]: #worker_worker_threadid
+[`vm.moveMessagePortToContext()`]: vm.html#vm_vm_movemessageporttocontext_port_context
+[vm]: vm.html#vm_vm_executing_javascript
 [`cluster` module]: cluster.html
 [`inspector`]: inspector.html
 [v8.serdes]: v8.html#v8_serialization_api

lib/vm.js

@@ -28,9 +28,11 @@ const {
   isContext: _isContext,
 } = process.binding('contextify');
 
+const { internalBinding } = require('internal/bootstrap/loaders');
 const { ERR_INVALID_ARG_TYPE } = require('internal/errors').codes;
 const { isUint8Array } = require('internal/util/types');
 const { validateInt32, validateUint32 } = require('internal/validators');
+const { moveMessagePortToContext } = internalBinding('messaging');
 
 class Script extends ContextifyScript {
   constructor(code, options = {}) {
@@ -290,6 +292,7 @@ module.exports = {
   Script,
   createContext,
   createScript,
+  moveMessagePortToContext,
   runInContext,
   runInNewContext,
   runInThisContext,

src/node_contextify.cc

@@ -26,9 +26,6 @@
 #include "node_contextify.h"
 #include "node_context_data.h"
 
-namespace node {
-namespace contextify {
-
 using v8::Array;
 using v8::ArrayBuffer;
 using v8::Boolean;
@@ -66,6 +63,9 @@ using v8::Value;
 using v8::WeakCallbackInfo;
 using v8::WeakCallbackType;
 
+namespace node {
+namespace contextify {
+
 // The vm module executes code in a sandboxed environment with a different
 // global object than the rest of the code. This is achieved by applying
 // every call that changes or queries a property on the global `this` in the
@@ -938,6 +938,20 @@ void Initialize(Local<Object> target,
 }
 
 }  // namespace contextify
+
+MaybeLocal<Context> ContextFromContextifiedSandbox(
+    Environment* env,
+    Local<Object> sandbox) {
+  using contextify::ContextifyContext;
+  ContextifyContext* contextify_context =
+      ContextifyContext::ContextFromContextifiedSandbox(env, sandbox);
+
+  if (contextify_context == nullptr)
+    return MaybeLocal<Context>();
+  else
+    return contextify_context->context();
+}
+
 }  // namespace node
 
 NODE_BUILTIN_MODULE_CONTEXT_AWARE(contextify, node::contextify::Initialize)

src/node_contextify.h

@@ -98,6 +98,11 @@ class ContextifyContext {
 };
 
 }  // namespace contextify
+
+v8::MaybeLocal<v8::Context> ContextFromContextifiedSandbox(
+    Environment* env,
+    v8::Local<v8::Object> sandbox);
+
 }  // namespace node
 
 #endif  // SRC_NODE_CONTEXTIFY_H_

src/node_messaging.cc

@@ -1,4 +1,5 @@
 #include "node_messaging.h"
+#include "node_contextify.h"
 #include "node_internals.h"
 #include "node_buffer.h"
 #include "node_errors.h"
@@ -606,6 +607,37 @@ void MessagePort::Stop(const FunctionCallbackInfo<Value>& args) {
   port->Stop();
 }
 
+void MessagePort::MoveToContext(const FunctionCallbackInfo<Value>& args) {
+  Environment* env = Environment::GetCurrent(args);
+  MessagePort* port;
+  if (!args[0]->IsObject() ||
+      (port = Unwrap<MessagePort>(args[0].As<Object>())) == nullptr) {
+    env->ThrowTypeError("First argument needs to be a MessagePort instance");
+  }
+  if (!port->data_) {
+    env->ThrowError("Cannot transfer a closed MessagePort");
+    return;
+  }
+  if (port->is_privileged_ || port->flagged_message_listener_) {
+    env->ThrowError("Cannot transfer MessagePort with special semantics");
+    return;
+  }
+  Local<Value> context_arg = args[1];
+  Local<Context> context;
+  if (!context_arg->IsObject() ||
+      !ContextFromContextifiedSandbox(env, context_arg.As<Object>())
+          .ToLocal(&context)) {
+    env->ThrowError("Invalid context argument");
+    return;
+  }
+  Context::Scope context_scope(context);
+  MessagePort* target =
+      MessagePort::New(env, context, nullptr, port->Detach());
+  if (target) {
+    args.GetReturnValue().Set(target->object());
+  }
+}
+
 size_t MessagePort::self_size() const {
   Mutex::ScopedLock lock(data_->mutex_);
   size_t sz = sizeof(*this) + sizeof(*data_);
@@ -689,6 +721,8 @@ static void InitMessaging(Local<Object> target,
                 templ->GetFunction(context).ToLocalChecked()).FromJust();
   }
 
+  env->SetMethod(target, "moveMessagePortToContext",
+                 MessagePort::MoveToContext);
   target->Set(context,
               env->message_port_constructor_string(),
               GetMessagePortConstructor(env, context).ToLocalChecked())

src/node_messaging.h

@@ -170,11 +170,16 @@ class MessagePort : public HandleWrap {
   // Stop processing messages on this port as a receiving end.
   void Stop();
 
+  /* constructor */
   static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
+  /* prototype methods */
   static void PostMessage(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void Start(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void Stop(const v8::FunctionCallbackInfo<v8::Value>& args);
 
+  /* static */
+  static void MoveToContext(const v8::FunctionCallbackInfo<v8::Value>& args);
+
   // Turns `a` and `b` into siblings, i.e. connects the sending side of one
   // to the receiving side of the other. This is not thread-safe.
   static void Entangle(MessagePort* a, MessagePort* b);

test/parallel/test-message-channel-move.js

@@ -0,0 +1,45 @@
+/* eslint-disable prefer-assert-methods */
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const vm = require('vm');
+const { MessageChannel } = require('worker');
+
+{
+  const context = vm.createContext();
+  const channel = new MessageChannel();
+  context.port = vm.moveMessagePortToContext(channel.port1, context);
+  context.global = context;
+  const port = channel.port2;
+  vm.runInContext('(' + function() {
+    function assert(condition) { if (!condition) throw new Error(); }
+
+    {
+      assert(port instanceof Object);
+      assert.strictEqual(port.onmessage, undefined);
+      assert(port.postMessage instanceof Function);
+      port.onmessage = function(msg) {
+        assert(msg instanceof Object);
+        port.postMessage(msg);
+      };
+      port.start();
+    }
+
+    {
+      let threw = false;
+      try {
+        port.postMessage(global);
+      } catch (e) {
+        assert(e instanceof Object);
+        assert(e instanceof Error);
+        threw = true;
+      }
+      assert(threw);
+    }
+  } + ')()', context);
+  port.on('message', common.mustCall((msg) => {
+    assert(msg instanceof Object);
+    port.close();
+  }));
+  port.postMessage({});
+}