module: use symbol in WeakMap to manage host defined options

Previously when managing the importModuleDynamically callback of
vm.compileFunction(), we use an ID number as the host defined option
and maintain a per-Environment ID -> CompiledFnEntry map to retain
the top-level referrer function returned by vm.compileFunction() in
order to pass it back to the callback, but it would leak because with
how we used v8::Persistent to maintain this reference, V8 would not
be able to understand the cycle and would just think that the
CompiledFnEntry was supposed to live forever. We made an attempt
to make that reference known to V8 by making the CompiledFnEntry weak
and using a private symbol to make CompiledFnEntry strongly
references the top-level referrer function in
nodejs#46785, but that turned out to be
unsound, because the there's no guarantee that the top-level function
must be alive while import() can still be initiated from that
function, since V8 could discard the top-level function and only keep
inner functions alive, so relying on the top-level function to keep
the CompiledFnEntry alive could result in use-after-free which caused
a revert of that fix.

With this patch we use a symbol in the host defined options instead of
a number, because with the stage-3 symbol-as-weakmap-keys proposal
we could directly use that symbol to keep the referrer alive using a
WeakMap. As a bonus this also keeps the other kinds of referrers
alive as long as import() can still be initiated from that
Script/Module, so this also fixes the long-standing crash caused by
vm.Script being GC'ed too early when its importModuleDynamically
callback still needs it.

Author: joyeecheung

lib/internal/modules/esm/create_dynamic_module.js

@@ -45,8 +45,9 @@ import.meta.done();
 
   if (imports.length)
     reflect.imports = { __proto__: null };
-  const { setCallbackForWrap } = require('internal/modules/esm/utils');
-  setCallbackForWrap(m, {
+  const { registerModule } = require('internal/modules/esm/utils');
+  registerModule(m, {
+    __proto__: null,
     initializeImportMeta: (meta, wrap) => {
       meta.exports = reflect.exports;
       if (reflect.imports)

lib/internal/modules/esm/loader.js

@@ -101,9 +101,10 @@ class DefaultModuleLoader {
   ) {
     const evalInstance = (url) => {
       const { ModuleWrap } = internalBinding('module_wrap');
-      const { setCallbackForWrap } = require('internal/modules/esm/utils');
+      const { registerModule } = require('internal/modules/esm/utils');
       const module = new ModuleWrap(url, undefined, source, 0, 0);
-      setCallbackForWrap(module, {
+      registerModule(module, {
+        __proto__: null,
         initializeImportMeta: (meta, wrap) => this.importMetaInitialize(meta, { url }),
         importModuleDynamically: (specifier, { url }, importAssertions) => {
           return this.import(specifier, url, importAssertions);

lib/internal/modules/esm/translators.js

@@ -114,8 +114,9 @@ translators.set('module', async function moduleStrategy(url, source, isMain) {
   maybeCacheSourceMap(url, source);
   debug(`Translating StandardModule ${url}`);
   const module = new ModuleWrap(url, undefined, source, 0, 0);
-  const { setCallbackForWrap } = require('internal/modules/esm/utils');
-  setCallbackForWrap(module, {
+  const { registerModule } = require('internal/modules/esm/utils');
+  registerModule(module, {
+    __proto__: null,
     initializeImportMeta: (meta, wrap) => this.importMetaInitialize(meta, { url }),
     importModuleDynamically,
   });

lib/internal/modules/esm/utils.js

@@ -8,6 +8,11 @@ const {
   ObjectFreeze,
 } = primordials;
 
+const {
+  privateSymbols: {
+    host_defined_option_symbol,
+  },
+} = internalBinding('util');
 const {
   ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING,
   ERR_INVALID_ARG_VALUE,
@@ -19,16 +24,8 @@ const {
   setImportModuleDynamicallyCallback,
   setInitializeImportMetaObjectCallback,
 } = internalBinding('module_wrap');
-const {
-  getModuleFromWrap,
-} = require('internal/vm/module');
 const assert = require('internal/assert');
 
-const callbackMap = new SafeWeakMap();
-function setCallbackForWrap(wrap, data) {
-  callbackMap.set(wrap, data);
-}
-
 let defaultConditions;
 function getDefaultConditions() {
   assert(defaultConditions !== undefined);
@@ -71,21 +68,47 @@ function getConditionsSet(conditions) {
   return getDefaultConditionsSet();
 }
 
-function initializeImportMetaObject(wrap, meta) {
-  if (callbackMap.has(wrap)) {
-    const { initializeImportMeta } = callbackMap.get(wrap);
+const moduleMap = new SafeWeakMap();
+
+/**
+ * V8 would make sure that as long as import() can still be initiated from
+ * the referer, the symbol referenced by |host_defined_option_symbol| should
+ * be alive, which in term would keep the settings object alive through the
+ * WeakMap, and in turn that keeps the referer object alive, which would be
+ * passed into the callbacks.
+ * The reference goes like this:
+ *   [v8::internal::Script] (via host defined options) ----1--> [id_symbol]
+ *   [referer wrap] (via host_defined_option_symbol) --------2------^  |
+ *                                  ^---------------3-------------------
+ *   1+3 makes sure that as long as import() can still be initiated, the
+ *   referer wrap is still around and can be passed into the callbacks.
+ *   2 is only there so that we can get the id symbol to configure the
+ *   weak map.
+ * @param {ModuleWrap|ContextifyScript|Function} referer
+ * @param {object} settings
+ */
+function registerModule(referer, settings) {
+  const id_symbol = referer[host_defined_option_symbol];
+  settings.referer = referer;  // To prevent it from being GC'ed.
+  moduleMap.set(id_symbol, settings);
+}
+
+// The native callback
+function initializeImportMetaObject(symbol, meta) {
+  if (moduleMap.has(symbol)) {
+    const { initializeImportMeta, referer, vmReferer } = moduleMap.get(symbol);
     if (initializeImportMeta !== undefined) {
-      meta = initializeImportMeta(meta, getModuleFromWrap(wrap) || wrap);
+      meta = initializeImportMeta(meta, vmReferer || referer);
     }
   }
 }
 
-async function importModuleDynamicallyCallback(wrap, specifier, assertions) {
-  if (callbackMap.has(wrap)) {
-    const { importModuleDynamically } = callbackMap.get(wrap);
+// The native callback
+async function importModuleDynamicallyCallback(symbol, specifier, assertions) {
+  if (moduleMap.has(symbol)) {
+    const { importModuleDynamically, referer, vmReferer } = moduleMap.get(symbol);
     if (importModuleDynamically !== undefined) {
-      return importModuleDynamically(
-        specifier, getModuleFromWrap(wrap) || wrap, assertions);
+      return importModuleDynamically(specifier, vmReferer || referer, assertions);
     }
   }
   throw new ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING();
@@ -168,7 +191,7 @@ async function initializeHooks() {
 }
 
 module.exports = {
-  setCallbackForWrap,
+  registerModule,
   initializeESM,
   initializeHooks,
   getDefaultConditions,

lib/internal/vm.js

@@ -100,9 +100,10 @@ function internalCompileFunction(code, params, options) {
     const { importModuleDynamicallyWrap } = require('internal/vm/module');
     const wrapped = importModuleDynamicallyWrap(importModuleDynamically);
     const func = result.function;
-    const { setCallbackForWrap } = require('internal/modules/esm/utils');
-    setCallbackForWrap(result.cacheKey, {
-      importModuleDynamically: (s, _k, i) => wrapped(s, func, i),
+    const { registerModule } = require('internal/modules/esm/utils');
+    registerModule(func, {
+      __proto__: null,
+      importModuleDynamically: wrapped,
     });
   }
 

lib/internal/vm/module.js

@@ -11,7 +11,6 @@ const {
   ObjectSetPrototypeOf,
   ReflectApply,
   SafePromiseAllReturnVoid,
-  SafeWeakMap,
   Symbol,
   SymbolToStringTag,
   TypeError,
@@ -69,7 +68,6 @@ const STATUS_MAP = {
 
 let globalModuleId = 0;
 const defaultModuleName = 'vm:module';
-const wrapToModuleMap = new SafeWeakMap();
 
 const kWrap = Symbol('kWrap');
 const kContext = Symbol('kContext');
@@ -120,25 +118,29 @@ class Module {
       });
     }
 
+    let settings = { __proto__: null };
     if (sourceText !== undefined) {
       this[kWrap] = new ModuleWrap(identifier, context, sourceText,
                                    options.lineOffset, options.columnOffset,
                                    options.cachedData);
-      const { setCallbackForWrap } = require('internal/modules/esm/utils');
-      setCallbackForWrap(this[kWrap], {
+      settings = {
         initializeImportMeta: options.initializeImportMeta,
         importModuleDynamically: options.importModuleDynamically ?
           importModuleDynamicallyWrap(options.importModuleDynamically) :
           undefined,
-      });
+      };
     } else {
       assert(syntheticEvaluationSteps);
       this[kWrap] = new ModuleWrap(identifier, context,
                                    syntheticExportNames,
                                    syntheticEvaluationSteps);
     }
 
-    wrapToModuleMap.set(this[kWrap], this);
+    // This will take precedence over the referrer as the object being
+    // passed into the callbacks.
+    settings.vmReferer = this;
+    const { registerModule } = require('internal/modules/esm/utils');
+    registerModule(this[kWrap], settings);
 
     this[kContext] = context;
   }
@@ -445,5 +447,4 @@ module.exports = {
   SourceTextModule,
   SyntheticModule,
   importModuleDynamicallyWrap,
-  getModuleFromWrap: (wrap) => wrapToModuleMap.get(wrap),
 };

lib/vm.js

@@ -106,8 +106,9 @@ class Script extends ContextifyScript {
       validateFunction(importModuleDynamically,
                        'options.importModuleDynamically');
       const { importModuleDynamicallyWrap } = require('internal/vm/module');
-      const { setCallbackForWrap } = require('internal/modules/esm/utils');
-      setCallbackForWrap(this, {
+      const { registerModule } = require('internal/modules/esm/utils');
+      registerModule(this, {
+        __proto__: null,
         importModuleDynamically:
           importModuleDynamicallyWrap(importModuleDynamically),
       });

src/env-inl.h

@@ -359,16 +359,6 @@ inline AliasedInt32Array& Environment::stream_base_state() {
   return stream_base_state_;
 }
 
-inline uint32_t Environment::get_next_module_id() {
-  return module_id_counter_++;
-}
-inline uint32_t Environment::get_next_script_id() {
-  return script_id_counter_++;
-}
-inline uint32_t Environment::get_next_function_id() {
-  return function_id_counter_++;
-}
-
 ShouldNotAbortOnUncaughtScope::ShouldNotAbortOnUncaughtScope(
     Environment* env)
     : env_(env) {

src/env.h

@@ -722,14 +722,6 @@ class Environment : public MemoryRetainer {
   builtins::BuiltinLoader* builtin_loader();
 
   std::unordered_multimap<int, loader::ModuleWrap*> hash_to_module_map;
-  std::unordered_map<uint32_t, loader::ModuleWrap*> id_to_module_map;
-  std::unordered_map<uint32_t, contextify::ContextifyScript*>
-      id_to_script_map;
-  std::unordered_map<uint32_t, contextify::CompiledFnEntry*> id_to_function_map;
-
-  inline uint32_t get_next_module_id();
-  inline uint32_t get_next_script_id();
-  inline uint32_t get_next_function_id();
 
   EnabledDebugList* enabled_debug_list() { return &enabled_debug_list_; }
 

src/env_properties.h

@@ -21,6 +21,7 @@
   V(arrow_message_private_symbol, "node:arrowMessage")                         \
   V(contextify_context_private_symbol, "node:contextify:context")              \
   V(decorated_private_symbol, "node:decorated")                                \
+  V(host_defined_option_symbol, "node:host_defined_option_symbol")             \
   V(napi_type_tag, "node:napi:type_tag")                                       \
   V(napi_wrapper, "node:napi:wrapper")                                         \
   V(untransferable_object_private_symbol, "node:untransferableObject")         \
@@ -339,7 +340,6 @@
   V(blocklist_constructor_template, v8::FunctionTemplate)                      \
   V(contextify_global_template, v8::ObjectTemplate)                            \
   V(contextify_wrapper_template, v8::ObjectTemplate)                           \
-  V(compiled_fn_entry_template, v8::ObjectTemplate)                            \
   V(crypto_key_object_handle_constructor, v8::FunctionTemplate)                \
   V(env_proxy_template, v8::ObjectTemplate)                                    \
   V(env_proxy_ctor_template, v8::FunctionTemplate)                             \