Prohibit nested VM operations

Author: kateinoigakukun

packages/npm-packages/ruby-wasm-wasi/src/index.ts

@@ -35,9 +35,8 @@ export class RubyVM {
   }
 
   constructor() {
-    // Wrap exported functions from Ruby VM to stop GC during the
-    // function call if the call stack has sandwitched JS frames
-    // like JS -> Ruby -> JS -> Ruby.
+    // Wrap exported functions from Ruby VM to prohibit nested VM operation
+    // if the call stack has sandwitched JS frames like JS -> Ruby -> JS -> Ruby.
     const proxyExports = (exports: RbAbi.RbAbiGuest) => {
       const excludedMethods: (keyof RbAbi.RbAbiGuest)[] = ["addToImports", "instantiate", "rbGcEnable", "rbGcDisable"];
       const excluded = ["constructor"].concat(excludedMethods);
@@ -49,16 +48,11 @@ export class RubyVM {
         const value = exports[key];
         if (typeof value === "function") {
           exports[key] = (...args: any[]) => {
-            const shouldStopGC = this.interfaceState.hasJSFrameAfterRbFrame;
-            let isAlreadyDisabled = false;
-            if (shouldStopGC) {
-              isAlreadyDisabled = exports.rbGcDisable();
+            const isNestedVMCall = this.interfaceState.hasJSFrameAfterRbFrame;
+            if (isNestedVMCall) {
+              throw new Error("Nested VM operation is prohibited. If you are trying to call RubyVM API environment through Ruby, please call it from JS environment directly.");
             }
-            const result = Reflect.apply(value, exports, args)
-            if (shouldStopGC && !isAlreadyDisabled) {
-              exports.rbGcEnable();
-            }
-            return result;
+            return Reflect.apply(value, exports, args)
           }
         }
       }

packages/npm-packages/ruby-wasm-wasi/test/gc.test.ts

@@ -83,7 +83,10 @@ describe("GC integration", () => {
     expect(o2.call("hash").toString()).toBe(o3.call("hash").toString());
   });
 
-  test("stop GC while having a sandwitched JS frame", async () => {
+  // TODO: Stopping GC while having a sandwitched JS frame is one of the options
+  // to make nested eval safe. But there is still a problem with Fiber switching,
+  // so this test is skipped for now.
+  test.skip("stop GC while having a sandwitched JS frame", async () => {
     const vm = await initRubyVM();
     const o = vm.eval(`
     require "js"

packages/npm-packages/ruby-wasm-wasi/test/vm.test.ts

@@ -119,4 +119,30 @@ eval:11:in \`<main>'`);
     expect(vm.eval(`"hello".encoding.name`).toString()).toBe("UTF-8");
     expect(vm.eval(`__ENCODING__.name`).toString()).toBe("UTF-8");
   });
+
+  // FIXME: The below two tests are now failing because we cannot make it safe
+  // to call eval within eval.
+  // See https://github.com/ruby/ruby.wasm/issues/219#issuecomment-1551758711
+  test.failing("Nested Fiber switch", async () => {
+    const vm = await initRubyVM();
+    const setVM = vm.eval(`proc { |vm| JS::RubyVM = vm }`)
+    setVM.call("call", vm.wrap(vm))
+    vm.eval(`
+    $f0 = Fiber.new {
+      JS::RubyVM.eval("$f1.resume")
+    }
+    $f1 = Fiber.new {}
+    $f0.resume
+    `)
+    vm.eval(`puts $q.inspect`)
+  })
+
+  test.failing("raise in nested eval", async () => {
+    const vm = await initRubyVM();
+    const setVM = vm.eval(`proc { |vm| JS::RubyVM = vm }`)
+    setVM.call("call", vm.wrap(vm))
+    expect(() => {
+      vm.eval(`JS::RubyVM.eval("raise 'Exception from nested eval'")`)
+    }).toThrowError("Exception from nested eval")
+  })
 });