Bug 1196975 - part4: waiveInterposition. r=billm

js/xpconnect/src/Sandbox.cpp

@@ -1025,6 +1025,7 @@ xpc::CreateSandboxObject(JSContext* cx, MutableHandleValue vp, nsISupports* prin
     priv->allowWaivers = options.allowWaivers;
     priv->writeToGlobalPrototype = options.writeToGlobalPrototype;
     priv->isWebExtensionContentScript = options.isWebExtensionContentScript;
+    priv->waiveInterposition = options.waiveInterposition;
 
     // Set up the wantXrays flag, which indicates whether xrays are desired even
     // for same-origin access.
@@ -1491,6 +1492,7 @@ SandboxOptions::Parse()
               ParseBoolean("wantComponents", &wantComponents) &&
               ParseBoolean("wantExportHelpers", &wantExportHelpers) &&
               ParseBoolean("isWebExtensionContentScript", &isWebExtensionContentScript) &&
+              ParseBoolean("waiveInterposition", &waiveInterposition) &&
               ParseString("sandboxName", sandboxName) &&
               ParseObject("sameZoneAs", &sameZoneAs) &&
               ParseBoolean("freshZone", &freshZone) &&

js/xpconnect/src/XPCJSRuntime.cpp

@@ -194,6 +194,7 @@ CompartmentPrivate::CompartmentPrivate(JSCompartment* c)
     , writeToGlobalPrototype(false)
     , skipWriteToGlobalPrototype(false)
     , isWebExtensionContentScript(false)
+    , waiveInterposition(false)
     , universalXPConnectEnabled(false)
     , forcePermissiveCOWs(false)
     , scriptability(c)

js/xpconnect/src/XPCWrappedNativeScope.cpp

@@ -139,9 +139,11 @@ XPCWrappedNativeScope::XPCWrappedNativeScope(JSContext* cx,
     JSAddonId* addonId = JS::AddonIdOfObject(aGlobal);
     if (gInterpositionMap) {
         bool isSystem = nsContentUtils::IsSystemPrincipal(principal);
-        if (InterpositionMap::Ptr p = gInterpositionMap->lookup(addonId)) {
+        bool waiveInterposition = priv->waiveInterposition;
+        InterpositionMap::Ptr interposition = gInterpositionMap->lookup(addonId);
+        if (!waiveInterposition && interposition) {
             MOZ_RELEASE_ASSERT(isSystem);
-            mInterposition = p->value();
+            mInterposition = interposition->value();
         }
         // We also want multiprocessCompatible add-ons to have a default interposition.
         if (!mInterposition && addonId && isSystem) {

js/xpconnect/src/xpcprivate.h

@@ -3475,6 +3475,7 @@ public:
         , wantComponents(true)
         , wantExportHelpers(false)
         , isWebExtensionContentScript(false)
+        , waiveInterposition(false)
         , proto(cx)
         , addonId(cx)
         , writeToGlobalPrototype(false)
@@ -3492,6 +3493,7 @@ public:
     bool wantComponents;
     bool wantExportHelpers;
     bool isWebExtensionContentScript;
+    bool waiveInterposition;
     JS::RootedObject proto;
     nsCString sandboxName;
     JS::RootedString addonId;
@@ -3732,6 +3734,11 @@ public:
     // various bits of special compatibility behavior.
     bool isWebExtensionContentScript;
 
+    // Even if an add-on needs interposition, it does not necessary need it
+    // for every scope. If this flag is set we waive interposition for this
+    // scope.
+    bool waiveInterposition;
+
     // This is only ever set during mochitest runs when enablePrivilege is called.
     // It's intended as a temporary stopgap measure until we can finish ripping out
     // enablePrivilege. Once set, this value is never unset (i.e., it doesn't follow