Bug 1905239 - Introduce HostGetCodeForEval hook for PerformEval. r=tschuster

See https://tc39.es/proposal-dynamic-code-brand-checks

Differential Revision: https://phabricator.services.mozilla.com/D229477

caps/nsScriptSecurityManager.cpp

@@ -1554,6 +1554,7 @@ void nsScriptSecurityManager::InitJSCallbacks(JSContext* aCx) {
 
   static const JSSecurityCallbacks securityCallbacks = {
       ContentSecurityPolicyPermitsJSAction,
+      nullptr,  // codeForEvalGets
       JSPrincipalsSubsume,
   };
 

js/public/Principals.h

@@ -92,8 +92,24 @@ enum class RuntimeCode { JS, WASM };
 typedef bool (*JSCSPEvalChecker)(JSContext* cx, JS::RuntimeCode kind,
                                  JS::HandleString code);
 
+/*
+ * Provide a string of code from an Object argument, to be used by eval.
+ * See JSContext::getCodeForEval() in vm/JSContext.cpp as well as
+ * https://tc39.es/proposal-dynamic-code-brand-checks/#sec-hostgetcodeforeval
+ *
+ * `code` is the JavaScript object passed by the user.
+ * `outCode` is the JavaScript string to be actually executed, with nullptr
+ *  meaning NO-CODE.
+ *
+ * Return false on failure, true on success. The |outCode| parameter should not
+ * be modified in case of failure.
+ */
+typedef bool (*JSCodeForEvalOp)(JSContext* cx, JS::HandleObject code,
+                                JS::MutableHandle<JSString*> outCode);
+
 struct JSSecurityCallbacks {
   JSCSPEvalChecker contentSecurityPolicyAllows;
+  JSCodeForEvalOp codeForEvalGets;
   JSSubsumesOp subsumes;
 };
 

js/src/builtin/Eval.cpp

@@ -239,21 +239,31 @@ static bool EvalKernel(JSContext* cx, HandleValue v, EvalType evalType,
                 env->is<GlobalLexicalEnvironmentObject>());
   AssertInnerizedEnvironmentChain(cx, *env);
 
-  // Step 2.
+  // "Dynamic Code Brand Checks" adds support for Object values.
-  if (!v.isString()) {
+  // https://tc39.es/proposal-dynamic-code-brand-checks/#sec-performeval
+  // Steps 2-4.
+  RootedString str(cx);
+  if (v.isString()) {
+    str = v.toString();
+  } else if (v.isObject()) {
+    RootedObject obj(cx, &v.toObject());
+    if (!cx->getCodeForEval(obj, &str)) {
+      return false;
+    }
+  }
+  if (!str) {
     vp.set(v);
     return true;
   }
 
-  // Steps 3-4.
+  // Steps 6-8.
-  RootedString str(cx, v.toString());
   if (!cx->isRuntimeCodeGenEnabled(JS::RuntimeCode::JS, str)) {
     JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
                               JSMSG_CSP_BLOCKED_EVAL);
     return false;
   }
 
-  // Step 5 ff.
+  // Step 9 ff.
 
   // Per ES5, indirect eval runs in the global scope. (eval is specified this
   // way so that the compiler can make assumptions about what bindings may or

js/src/jsapi-tests/moz.build

@@ -40,6 +40,7 @@ UNIFIED_SOURCES += [
     "testDeflateStringToUTF8Buffer.cpp",
     "testDeleteProperty.cpp",
     "testDifferentNewTargetInvokeConstructor.cpp",
+    "testDynamicCodeBrandChecks.cpp",
     "testEmptyWindowIsOmitted.cpp",
     "testErrorCopying.cpp",
     "testErrorLineOfContext.cpp",

js/src/jsapi-tests/testDynamicCodeBrandChecks.cpp

@@ -0,0 +1,94 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ *
+ * Tests that the column number of error reports is properly copied over from
+ * other reports when invoked from the C++ api.
+ */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "jsapi-tests/tests.h"
+
+BEGIN_TEST(testDynamicCodeBrandChecks_DefaultHostGetCodeForEval) {
+  JS::RootedValue v(cx);
+
+  // String arguments are evaluated.
+  EVAL("eval('5*8');", &v);
+  CHECK(v.isNumber() && v.toNumber() == 40);
+
+  // Other arguments are returned as is by eval.
+  EVAL("eval({myProp: 41});", &v);
+  CHECK(v.isObject());
+  JS::RootedObject obj(cx, &v.toObject());
+  JS::RootedValue myProp(cx);
+  CHECK(JS_GetProperty(cx, obj, "myProp", &myProp));
+  CHECK(myProp.isNumber() && myProp.toNumber() == 41);
+
+  EVAL("eval({trustedCode: '6*7'}).trustedCode;", &v);
+  CHECK(v.isString());
+  JSString* str = v.toString();
+  CHECK(JS_LinearStringEqualsLiteral(JS_ASSERT_STRING_IS_LINEAR(str), "6*7"));
+
+  EVAL("eval({trustedCode: 42}).trustedCode;", &v);
+  CHECK(v.isNumber() && v.toNumber() == 42);
+
+  return true;
+}
+END_TEST(testDynamicCodeBrandChecks_DefaultHostGetCodeForEval)
+
+static bool ExtractTrustedCodeStringProperty(
+    JSContext* aCx, JS::Handle<JSObject*> aCode,
+    JS::MutableHandle<JSString*> outCode) {
+  JS::RootedValue value(aCx);
+  if (!JS_GetProperty(aCx, aCode, "trustedCode", &value)) {
+    return false;
+  }
+  if (value.isUndefined()) {
+    // If the property is undefined, return NO-CODE.
+    outCode.set(nullptr);
+    return true;
+  }
+  if (value.isString()) {
+    // If the property is a string, return it.
+    outCode.set(value.toString());
+    return true;
+  }
+  // Otherwise, emulate a failure.
+  JS_ReportErrorASCII(aCx, "Unsupported value for trustedCode property");
+  return false;
+}
+
+BEGIN_TEST(testDynamicCodeBrandChecks_CustomHostGetCodeForEval) {
+  JSSecurityCallbacks securityCallbacksWithEvalAcceptingObject = {
+      nullptr,                           // contentSecurityPolicyAllows
+      ExtractTrustedCodeStringProperty,  // codeForEvalGets
+      nullptr                            // subsumes
+  };
+  JS_SetSecurityCallbacks(cx, &securityCallbacksWithEvalAcceptingObject);
+  JS::RootedValue v(cx);
+
+  // String arguments are evaluated.
+  EVAL("eval('5*8');", &v);
+  CHECK(v.isNumber() && v.toNumber() == 40);
+
+  // Other arguments are returned as is by eval...
+  EVAL("eval({myProp: 41});", &v);
+  CHECK(v.isObject());
+  JS::RootedObject obj(cx, &v.toObject());
+  JS::RootedValue myProp(cx);
+  CHECK(JS_GetProperty(cx, obj, "myProp", &myProp));
+  CHECK(myProp.isNumber() && myProp.toNumber() == 41);
+
+  // ... but Objects are first tentatively converted to String by the
+  // codeForEvalGets callback.
+  EVAL("eval({trustedCode: '6*7'});", &v);
+  CHECK(v.isNumber() && v.toNumber() == 6 * 7);
+
+  // And if that codeForEvalGets callback fails, then so does the eval call.
+  CHECK(!execDontReport("eval({trustedCode: 6*7});", __FILE__, __LINE__));
+  cx->clearPendingException();
+
+  return true;
+}
+END_TEST(testDynamicCodeBrandChecks_CustomHostGetCodeForEval)

js/src/jsapi-tests/testStructuredClone.cpp

@@ -258,6 +258,7 @@ struct StructuredCloneTestPrincipals final : public JSPrincipals {
 
 JSSecurityCallbacks StructuredCloneTestPrincipals::securityCallbacks = {
     nullptr,  // contentSecurityPolicyAllows
+    nullptr,  // codeForEvalGets
     subsumes};
 
 BEGIN_TEST(testStructuredClone_SavedFrame) {

js/src/shell/js.cpp

@@ -955,6 +955,7 @@ class ShellPrincipals final : public JSPrincipals {
 
 JSSecurityCallbacks ShellPrincipals::securityCallbacks = {
     nullptr,  // contentSecurityPolicyAllows
+    nullptr,  // codeForEvalGets
     subsumes};
 
 // The fully-trusted principal subsumes all other principals.

js/src/vm/JSContext.cpp

@@ -1245,6 +1245,17 @@ bool JSContext::isRuntimeCodeGenEnabled(JS::RuntimeCode kind,
   return true;
 }
 
+bool JSContext::getCodeForEval(HandleObject code,
+                               JS::MutableHandle<JSString*> outCode) {
+  if (JSCodeForEvalOp gets = runtime()->securityCallbacks->codeForEvalGets) {
+    return gets(this, code, outCode);
+  }
+  // Default implementation from the "Dynamic Code Brand Checks" spec.
+  // https://tc39.es/proposal-dynamic-code-brand-checks/#sec-hostgetcodeforeval
+  outCode.set(nullptr);
+  return true;
+}
+
 size_t JSContext::sizeOfExcludingThis(
     mozilla::MallocSizeOf mallocSizeOf) const {
   /*

js/src/vm/JSContext.h

@@ -805,6 +805,10 @@ struct JS_PUBLIC_API JSContext : public JS::RootingContext,
   // runtime code generation "unsafe-eval", or "wasm-unsafe-eval" for Wasm.
   bool isRuntimeCodeGenEnabled(JS::RuntimeCode kind, js::HandleString code);
 
+  // Get code to be used by eval for Object argument.
+  bool getCodeForEval(JS::HandleObject code,
+                      JS::MutableHandle<JSString*> outCode);
+
   size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const;
   size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const;