Briefly demo'd MetaMask/metamask-mobile#8009, a minimally transformed ses@0.18.8 wip that runs on Hermes (latest React Native default JS engine)

here's the omnibus of issues/mods below, while figuring which parts we definitely need (vs can skip/remove in a codemod) cc @erights would appreciate any thoughts

Bundling (Metro, release)

• error: async functions are unsupported
  • loadWithoutErrorAnnotation
  • memoizedLoadWithErrorAnnotation
  • load
  • drainQueue (ses@1.5.0)
  • asyncTrampoline (ses@master)
  • fixed in Hermes SES shim variant
    • d04d591 leotm/RN07117SES@ebc6ed6
• error: async generators are unsupported
  • async function* AsyncGeneratorFunctionInstance() {}
  • fixed in Hermes SES shim variant
    • 0421ca7 leotm/RN07117SES@8a64849

• SES shim variant for Hermes compiler
  • feat(ses): Shim compatible with Hermes compiler #2334

Runtime

• // assertDirectEvalAvailable(); // SES TypeError
  • Feature Request: local eval for SES (Secure EcmaScript) support facebook/hermes#957
    • Implement Local Eval facebook/hermes#1515
  • Feature Request: with statement for SES (Secure EcmaScript) support facebook/hermes#1056
    • Add with statement support facebook/hermes#1571
  • DRAFT master...ses-hermes-p2
  • feat(ses): update lockdown init and enable Hermes VM #2723
• addIntrinsics(tameRegExpConstructor(regExpTaming)); // SES TypeError
  • feat(ses): tolerate omitted species #2108
• addIntrinsics(tameSymbolConstructor()); // Metro exception, RN polyfill error guard Fatal Error
  • feat(ses): redefine SharedSymbol to bypass Hermes prototype bug on obj literal short-hand methods #2206
• addIntrinsics(getAnonymousIntrinsics()); // SES TypeError
  • reappeared since updating SES
  • feat(ses): fix undefined AsyncGenerator prototype on Hermes #2220
  • feat(ses): fix conflicting definitions of %InertAsyncFunction% on Hermes #2221
  • fixed in Hermes-specific SES shim variant
• completePrototypes(); // SES TypeError
  • fix(ses): completePrototypes on Hermes #2563
  • Function prototype set to undefined inconsistently too late #2598
  • fix(ses): fix #2598 with cauterizeProperty reuse #2624
• whitelistIntrinsics(intrinsics, markVirtualizedNativeFunction); // SES TypeError
  • nb: now renamed to removeUnpermittedIntrinsics
  • fix(ses): removeUnpermittedIntrinsics on Hermes #2655
  • Strictness, caller and arguments spec compliancy facebook/hermes#1582
  • facebook/hermes@bb90b33

Non blocking

• SES lockdown Hermes improvements tracking issue #2761

Tested across bundled Hermes for RN

• 0.12.0 (old standalone playground compiler & vm, esvu fails to fetch Hermes to plug into eshost)
• 0.71.15 (metamask-mobile): built from source
  • from: https://github.com/MetaMask/hermes (our fork)
• 0.71.17: hermes-2023-03-07-RNv0.71.4-xxx: Increase default max stack size (#923)
  • from: https://github.com/facebook/hermes/tree/rn/0.71-stable
  • uses: https://github.com/facebook/flipper/releases/tag/v0.125.0
  • debugger statements pause exec, works once after Metro w Hermes Debugger then broken on Hot Reload
• 0.72.12 (metamask-mobile@next): hermes-2023-08-07-RNv0.72.4-xxx: Avoid repeated branches while iterating StringView no longer build from source
  • from: https://github.com/facebook/hermes/tree/rn/0.72-stable
  • uses: https://github.com/facebook/flipper/releases/tag/v0.182.0
  • debugger statements pause exec, but Hermes Debugger broken
• 0.73.6 (JDK 17): hermes-2024-02-20-RNv0.73.5-xxx: Mitigate WeakMap cycle leak
  • from: https://github.com/facebook/hermes/tree/rn/0.73-stable
  • uses: https://github.com/facebook/flipper/releases/tag/v0.201.0
  • debugger statements pause exec, but Hermes Debugger broken and deprecated, new debugger same
    • [0.73, 0.74] Experimental New Debugger — Known Issues and Feedback react-native-community/discussions-and-proposals#733 (comment)
    • [0.73, 0.74] Experimental New Debugger — Known Issues and Feedback react-native-community/discussions-and-proposals#733 (comment)
• 0.74.0-rc.3: hermes-2024-02-20-RNv0.74.0-xxx: Save exported state across RuntimeAgent instances
• Nightly?: hermes-2024-03-26-RNvmain-xxx: breakAtPossibleNextInstructions should use const InterpreterState
  • from: https://github.com/facebook/hermes/commits/main
• RNTester/RNTestProject?
  • https://github.com/reactwg/react-native-releases/blob/main/docs/guide-release-testing.md

Nb: latest minor version tags above, side-by-side with Hermes tarballs downloaded during build

async functions

# ...

metamask-mobile/android/app/build/ASSETS/createBundleProdDebugJsAndAssets/index.android.bundle: error: async functions are unsupported
      const loadWithoutErrorAnnotation = async (compartmentPrivateFields, moduleAliases, compartment, moduleSpecifier, pendingJobs, moduleLoads, errors) => {

metamask-mobile/android/app/build/ASSETS/createBundleProdDebugJsAndAssets/index.android.bundle: error: async functions are unsupported
      const memoizedLoadWithErrorAnnotation = async (compartmentPrivateFields, moduleAliases, compartment, moduleSpecifier, pendingJobs, moduleLoads, errors) => {

metamask-mobile/android/app/build/ASSETS/createBundleProdDebugJsAndAssets/index.android.bundle: error: async functions are unsupported
      const load = async (compartmentPrivateFields, moduleAliases, compartment, moduleSpecifier) => {

mobile/android/app/build/ASSETS/createBundleProdDebugJsAndAssets/index.android.bundle:1233 error: async generators are unsupported
        async function* AsyncGeneratorFunctionInstance() {}

# ...

Nb: async function* a() {}; alone won't emit an error
but using/referencing it and beyond const b = a; will

encountered bundling the app with Metro (considering Re.Pack)

# via RN CLI
yarn watch:clean
yarn start:android # react-native run-android --variant=prodDebug

# or via Gradle Wrapper
./gradlew clean # after changes to SES
./gradlew :app:createBundleProdDebugJsAndAssets # bundle only
./gradlew :app:installProdDebug -PreactNativeArchitectures=arm64-v8a # bundle then build for M2

Since Hermes async and await support is In Progress (let alone async generators)

so Hermes doesn't support async arrow functions directly

but we're getting indirect support later via @babel/preset-env

• includes @babel/plugin-transform-async-to-generator in ES2017
  which lowers them to generator fns or plain fns using regenerator (relies on regenerator-runtime)
  • we require facebook/regenerator@903a507 for SES
  • i.e. regenerator-runtime@0.13.8+
• includes @babel/plugin-transform-arrow-functions
• includes @babel/plugin-transform-async-generator-functions in ES2018
• includes @babel/plugin-async-generator-functions in ES2018 (unused)

# regenerator-runtime
metamask@7.15.0 /Users/leo/Documents/GitHub/metamask-mobile
├─┬ @babel/runtime@7.23.2
│ └── regenerator-runtime@0.14.0
# ...

# (old name: babel-plugin-transform-async-to-generator)
metamask@7.15.0 /Users/leo/Documents/GitHub/metamask-mobile
├─┬ @babel/preset-env@7.23.2
│ └── @babel/plugin-transform-async-to-generator@7.22.5
└─┬ metro-react-native-babel-preset@0.73.10
  └── @babel/plugin-transform-async-to-generator@7.22.5 deduped

# @babel/plugin-transform-arrow-functions
metamask@7.15.0 /Users/leo/Documents/GitHub/metamask-mobile
├─┬ @babel/preset-env@7.23.2
│ └── @babel/plugin-transform-arrow-functions@7.22.5
├─┬ fbjs-scripts@3.0.1
│ └─┬ babel-preset-fbjs@3.4.0
│   └── @babel/plugin-transform-arrow-functions@7.22.5 deduped
├─┬ metro-react-native-babel-preset@0.73.10
│ └── @babel/plugin-transform-arrow-functions@7.22.5 deduped
└─┬ react-native-reanimated@3.1.0
  └── @babel/plugin-transform-arrow-functions@7.22.5 deduped

# @babel/plugin-transform-async-generator-functions
└─┬ @babel/preset-env@7.24.4
  └── @babel/plugin-transform-async-generator-functions@7.24.3

# @babel/plugin-async-generator-functions
metamask@7.15.0 /Users/leo/Documents/GitHub/metamask-mobile
└── (empty)

nb: metro-react-native-babel-preset@0.77.0 includes these 37 babel plugins

If so, re-write to Promises, otherwise skip parts or remove and refactor, or is there a better solution?

TODO: check refactor from async arrow fns to async fns; check latest bundled Hermes versions of RN

No longer an issue on bundled Hermes for RN 0.71.17+ (i.e. not a custom build from source)

assertDirectEvalAvailable

Since eval is Excluded From Support

• Feature Request: local eval for SES (Secure EcmaScript) support facebook/hermes#957

tameRegExpConstructor

no RegExp[Symbol.species] descriptor, no stack

ses.cjs#4472: TypeError('no RegExp[Symbol.species] descriptor');

// node_modules/typescript/lib/lib.es2015.symbol.wellknown.d.ts
// ...
/// <reference lib="es2015.symbol" />

interface SymbolConstructor {
// ...
    /**
     * A function valued property that is the constructor function that is used to create
     * derived objects.
     */
    readonly species: unique symbol;
// ...
}

This is because it is Excluded From Support on Hermes

Symbol.species and its interactions with JS library functions

For a good reason it seems, noting both warnings

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/species

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/@@species

So we likely want this part skipped or tameRegExpConstructor option to skip (plus remaining changes, then upstream)

    if( !speciesDesc) {
      throw TypeError('no RegExp[Symbol.species] descriptor'); // Thrown on Hermes since excluded from support
     }

fixed in

• feat(ses): tolerate omitted species #2108

tameSymbolConstructor

property is not configurable, no stack / at [object CallSite]

ses.cjs#9481: defineProperties(SharedSymbol, descs);

We can fix this simply by omitting configurable: true on Hermes

  const descs = fromEntries(
    arrayMap(originalDescsEntries, ([name, desc]) => [
      name,
      { ...desc }, // configurable: true, omitted
    ]),
  );

in order to tame the Symbol constructor (used on constructed compartments),
we attempt to temporarily make all props configurable: true
so that we can whitelist (remove non-standard) props, then harden them (back to non-configurable)

Hermes has 15 Symbol props on all versions (contrasted to e.g. Node with 18)

on metamask-mobile (Android)
when we observe Object.getOwnPropertyDescriptor(originalDescsEntries, name)?.configurable
we get 15 non-true props: 1 false prop (length), 14 undefined

nb: on Hermes v0.12.0 built from scratch

➜  bin ./hermes --version
LLVM (http://llvm.org/):
  LLVH version 8.0.0svn
  Optimized build

Hermes JavaScript compiler and Virtual Machine.
  Hermes release version: 0.12.0
  HBC bytecode version: 96

  Features:
    Debugger
    Zip file input
➜  bin ./hermes
>> Object.getOwnPropertyDescriptors(Symbol)
{ length: { value: 0, writable: false, enumerable: false, configurable: true }, name: { value: "Symbol", writable: false, enumerable: false, configurable: true }, prototype: { value: Symbol { [constructor]: [Function Symbol], [description]: [accessor], [toString]: [Function toString], [valueOf]: [Function valueOf], [Symbol(Symbol.toStringTag)]: "Symbol", [Symbol(Symbol.toPrimitive)]: [Function [Symbol.toPrimitive]] }, writable: false, enumerable: false, configurable: false }, for: { value: [Function for], writable: true, enumerable: false, configurable: true }, keyFor: { value: [Function keyFor], writable: true, enumerable: false, configurable: true }, hasInstance: { value: Symbol(Symbol.hasInstance), writable: false, enumerable: false, configurable: false }, iterator: { value: Symbol(Symbol.iterator), writable: false, enumerable: false, configurable: false }, isConcatSpreadable: { value: Symbol(Symbol.isConcatSpreadable), writable: false, enumerable: false, configurable: false }, toPrimitive: { value: Symbol(Symbol.toPrimitive), writable: false, enumerable: false, configurable: false }, toStringTag: { value: Symbol(Symbol.toStringTag), writable: false, enumerable: false, configurable: false }, match: { value: Symbol(Symbol.match), writable: false, enumerable: false, configurable: false }, matchAll: { value: Symbol(Symbol.matchAll), writable: false, enumerable: false, configurable: false }, search: { value: Symbol(Symbol.search), writable: false, enumerable: false, configurable: false }, replace: { value: Symbol(Symbol.replace), writable: false, enumerable: false, configurable: false }, split: { value: Symbol(Symbol.split), writable: false, enumerable: false, configurable: false } }

(i built/ran Hermes from scratch to observe above, since Hermes via eshost-cli on m2 is unsupported via jsvu(mac64arm) and doesn't fetch via esvu(darwin-arm64) and built Hermes via eshost complains hermes: Unknown command line argument '-fenable-tdz' and Hermes playground only prints [object Object] - but thx for demo'ing @gibson042, jealous how it worked so eloquently on your machine :p)

nb: some Hermes Language Features

• excludes: Symbol.species and its interactions with JS library functions
• excludes: Symbol.unscopables (Hermes does not support with)
• in progress: Symbol.prototype.description (it's not fully spec-conformant yet. Symbol().description should be undefined but it's currently '')
• supports: Iteration (with [Symbol.iterator])
• supports: Symbols (including most well-known Symbols)

nb: our tameSymbolConstructor fn

// https://github.com/endojs/endo/blob/master/packages/ses/src/tame-symbol-constructor.js
/**
 * This taming provides a tamed alternative to the original `Symbol` constructor
 * that starts off identical, except that all its properties are "temporarily"
 * configurable. The original `Symbol` constructor remains unmodified on
 * the start compartment's global. The tamed alternative is used as the shared
 * `Symbol` constructor on constructed compartments.
 *
 * Starting these properties as configurable assumes two succeeding phases of
 * processing: A whitelisting phase, that
 * removes all properties not on the whitelist (which requires them to be
 * configurable) and a global hardening step that freezes all primordials,
 * returning these properties to their expected non-configurable status.
 *
 * The ses shim is constructed to eventually enable vetted shims to run between
 * repair and global hardening. However, such vetted shims would normally
 * run in the start compartment, which continues to use the original unmodified
 * `Symbol`, so they should not normally be affected by the temporary
 * configurability of these properties.
 *
 * Note that the spec refers to the global `Symbol` function as the
 * ["Symbol Constructor"](https://tc39.es/ecma262/multipage/fundamental-objects.html#sec-symbol-constructor)
 * even though it has a call behavior (can be called as a function) and does not
 * not have a construct behavior (cannot be called with `new`). Accordingly,
 * to tame it, we must replace it with a function without a construct
 * behavior.
 */

nb: a SymbolTaming lockdown option doesn't exist yet (same with FunctionTaming on tameFunctionConstructors)

solutions

• tolerate this in ses shim (codemod, or upstream: packages/ses/src/tame-symbol-constructor.js)
• add a lockdown option (upstream: packages/ses/src/lockdown.js#L276)
  • default: safe (current implementation)
  • option: unsafe (skip taming, none at all)

extra

• instead of throwing a RN polyfill error-guard Fatal Error in Metro on Hermes, throw a similar SES TypeError before instead? unless tolerated
• update The ses shim is constructed to _eventually_ enable vetted shims... 10mo ago now we have vetted shims
  • and remaining codebase refs

security considerations pending further thought

getAnonymousIntrinsics

⚠️ Babel is likely transforming SES, check the config to ensure the shim is ignored ⚠️

Conflicting definitions of %InertAsyncFunction%, no stack

ses.cjs#3688: TypeError( `Conflicting definitions of ${name}`);

Not present in

• hermes-engine-cli@0.12.0
• react-native@0.71.17
  • debugger statements working in Flipper > Hermes Debugger (RN)

Present in

• react-native@0.72.15(metamask-mobile)
  • debugger statements broken in Flipper > Hermes Debugger (RN)

commenting

throw new TypeError(`Conflicting definitions of ${name}`);

results in SES continuing to lockdown
resulting in a fully functional React Native app
but at what security cost

%InertFunction% // no conflicting definitions
%InertAsyncFunction% // ❌ conflicting definitions
%InertGeneratorFunction% // no conflicting definitions

completePrototypes

lockdown.prototype property not whitelisted, no stack

ses.cjs#3730: TypeError( `${name}.prototype property not whitelisted`)

to repro, uncomment

whitelistIntrinsics

Unexpected intrinsic intrinsics.isFinite.__proto__ at %FunctionPrototype%, no stack

ses.cjs#3953: TypeError( `Unexpected intrinsic ${path}.__proto__ at ${protoName}`)

isFinite appears to be the first of many intrinsics

No more SES TypeErrors thrown after whitelisting intrinsics

hardenIntrinsics

No errors visible, but the React Native app hangs

__hardenTaming__: 'unsafe' (default safe) fixes the issue, but is not a viable solution

https://github.com/endojs/endo/blob/master/packages/ses/docs/lockdown.md#__hardentaming__-options

The Hermes VM throws

Error running main: (TypeError#1)
TypeError#1: Failed to load module "./index.js" in package "file:///Users/leo/Documents/GitHub/endo/packages/ses/" (1 underlying failures: Error transforming "mjs" source in "file:///Users/leo/Documents/GitHub/endo/packages/ses/index.js": Cannot assign to read only property 'toString' of function 'function (path) {
    if (validator.call(path)) {
      return fn.apply(this, arguments);
    }
  }'

  at throwAggregateError (packages/ses/src/module-load.js:546:11)
  at load (packages/ses/src/module-load.js:594:3)
  at async makeBundle (packages/compartment-mapper/src/bundle.js:292:3)
  at async writeBundle (packages/ses/scripts/bundle.js:50:18)
  at async main (packages/ses/scripts/bundle.js:107:3)