Bug 1755979: Pass accessibilty resource ID down from the parent. r=Jamie,nika

This is being done because the way the ID is determined causes issue with the
sandbox and the ID is required very early in process start up.

Differential Revision: https://phabricator.services.mozilla.com/D139649

dom/ipc/ContentParent.cpp

@@ -33,6 +33,8 @@
 #if defined(XP_WIN) && defined(ACCESSIBILITY)
 #  include "mozilla/a11y/AccessibleWrap.h"
 #  include "mozilla/a11y/Compatibility.h"
+#  include "mozilla/mscom/ActCtxResource.h"
+#  include "mozilla/StaticPrefs_accessibility.h"
 #endif
 #include <map>
 #include <utility>
@@ -2526,6 +2528,20 @@ bool ContentParent::BeginSubprocessLaunch(ProcessPriority aPriority) {
   // processes.
   ::mozilla::ipc::ExportSharedJSInit(*mSubprocess, extraArgs);
 
+#if defined(XP_WIN) && defined(ACCESSIBILITY)
+  // Determining the accessibility resource ID causes problems with the sandbox,
+  // so we pass it on the command line as it is required very early in process
+  // start up. It is not required when the caching mechanism is being used.
+  if (!StaticPrefs::accessibility_cache_enabled_AtStartup()) {
+    // The accessibility resource ID may not be set in some cases, for example
+    // in xpcshell tests.
+    auto resourceId = mscom::ActCtxResource::GetAccessibilityResourceId();
+    if (resourceId) {
+      geckoargs::sA11yResourceId.Put(resourceId, extraArgs);
+    }
+  }
+#endif
+
   // Register ContentParent as an observer for changes to any pref
   // whose prefix matches the empty string, i.e. all of them.  The
   // observation starts here in order to capture pref updates that

ipc/mscom/ProcessRuntime.cpp

@@ -59,7 +59,9 @@ ProcessRuntime::ProcessRuntime(const ProcessCategory aProcessCategory)
 #  if defined(MOZILLA_INTERNAL_API)
   // If we're inside XUL, and we're the parent process, then we trust that
   // this has already been initialized for us prior to XUL being loaded.
-  if (aProcessCategory != ProcessCategory::GeckoBrowserParent) {
+  // Only required in the child if the Resource ID has been passed down.
+  if (aProcessCategory != ProcessCategory::GeckoBrowserParent &&
+      ActCtxResource::GetAccessibilityResourceId()) {
     mActCtxRgn.emplace(ActCtxResource::GetAccessibilityResource());
   }
 #  elif defined(MOZ_HAS_MOZGLUE)

ipc/mscom/mozglue/ActCtxResource.cpp

@@ -195,23 +195,43 @@ static HMODULE GetContainingModuleHandle() {
   return thisModule;
 }
 
+static uint16_t sActCtxResourceId = 0;
+
+/* static */
+void ActCtxResource::SetAccessibilityResourceId(uint16_t aResourceId) {
+  sActCtxResourceId = aResourceId;
+}
+
+/* static */
+uint16_t ActCtxResource::GetAccessibilityResourceId() {
+  return sActCtxResourceId;
+}
+
+static void EnsureAccessibilityResourceId() {
+  if (!sActCtxResourceId) {
+#if defined(HAVE_64BIT_BUILD)
+    // The manifest for 64-bit Windows is embedded with resource ID 64.
+    sActCtxResourceId = 64;
+#else
+    // The manifest for 32-bit Windows is embedded with resource ID 32.
+    // Beginning with Windows 10 Creators Update, 32-bit builds always use the
+    // 64-bit manifest. Older builds of Windows may or may not require the
+    // 64-bit manifest: UseIAccessibleProxyStub() determines the course of
+    // action.
+    if (mozilla::IsWin10CreatorsUpdateOrLater() || UseIAccessibleProxyStub()) {
+      sActCtxResourceId = 64;
+    } else {
+      sActCtxResourceId = 32;
+    }
+#endif  // defined(HAVE_64BIT_BUILD)
+  }
+}
+
 ActCtxResource ActCtxResource::GetAccessibilityResource() {
   ActCtxResource result = {};
   result.mModule = GetContainingModuleHandle();
-#if defined(HAVE_64BIT_BUILD)
-  // The manifest for 64-bit Windows is embedded with resource ID 64.
-  result.mId = 64;
-#else
-  // The manifest for 32-bit Windows is embedded with resource ID 32.
-  // Beginning with Windows 10 Creators Update, 32-bit builds always use the
-  // 64-bit manifest. Older builds of Windows may or may not require the 64-bit
-  // manifest: UseIAccessibleProxyStub() determines the course of action.
-  if (mozilla::IsWin10CreatorsUpdateOrLater() || UseIAccessibleProxyStub()) {
-    result.mId = 64;
-  } else {
-    result.mId = 32;
-  }
-#endif  // defined(HAVE_64BIT_BUILD)
+  EnsureAccessibilityResourceId();
+  result.mId = GetAccessibilityResourceId();
   return result;
 }
 

ipc/mscom/mozglue/ActCtxResource.h

@@ -16,6 +16,17 @@ struct ActCtxResource {
   uint16_t mId;
   HMODULE mModule;
 
+  /**
+   * Set the resource ID used by GetAccessibilityResource. This is so that
+   * sandboxed child processes can use a value passed down from the parent.
+   */
+  static MFBT_API void SetAccessibilityResourceId(uint16_t aResourceId);
+
+  /**
+   * Get the resource ID used by GetAccessibilityResource.
+   */
+  static MFBT_API uint16_t GetAccessibilityResourceId();
+
   /**
    * @return ActCtxResource of a11y manifest resource to be passed to
    * mscom::ActivationContext

toolkit/xre/GeckoArgs.h

@@ -129,6 +129,11 @@ static CommandLineArg<bool> sSafeMode{"-safeMode", "safemode"};
 static CommandLineArg<bool> sIsForBrowser{"-isForBrowser", "isforbrowser"};
 static CommandLineArg<bool> sNotForBrowser{"-notForBrowser", "notforbrowser"};
 
+#if defined(XP_WIN) && defined(ACCESSIBILITY)
+static CommandLineArg<uint64_t> sA11yResourceId{"-a11yResourceId",
+                                                "a11yresourceid"};
+#endif  // defined(XP_WIN) && defined(ACCESSIBILITY)
+
 #if defined(__GNUC__)
 #  pragma GCC diagnostic pop
 #endif

toolkit/xre/nsEmbedFunctions.cpp

@@ -27,6 +27,10 @@
 #  include "mozilla/ScopeExit.h"
 #  include "mozilla/WinDllServices.h"
 #  include "WinUtils.h"
+#  ifdef ACCESSIBILITY
+#    include "mozilla/GeckoArgs.h"
+#    include "mozilla/mscom/ActCtxResource.h"
+#  endif
 #endif
 
 #include "nsAppRunner.h"
@@ -620,6 +624,16 @@ nsresult XRE_InitChildProcess(int aArgc, char* aArgv[],
     // Associate this thread with a UI MessageLoop
     MessageLoop uiMessageLoop(uiLoopType);
     {
+#if defined(XP_WIN) && defined(ACCESSIBILITY)
+      // The accessibility resource ID is passed down on the command line
+      // because its retrieval causes issues with the sandbox. When it is set,
+      // it is required for ProcessRuntime construction within ProcessChild.
+      auto a11yResourceId = geckoargs::sA11yResourceId.Get(aArgc, aArgv);
+      if (a11yResourceId.isSome()) {
+        mscom::ActCtxResource::SetAccessibilityResourceId(*a11yResourceId);
+      }
+#endif
+
       UniquePtr<ProcessChild> process;
       switch (XRE_GetProcessType()) {
         case GeckoProcessType_Default: