Bug 41901: Hardcode normalized FontSubstitutes.

Windows has a system to set font aliases through the registry.
This allows some customization that could be used as a fingerprinting
vector.
Moreover, this mechanism is used by Windows itself, and different SKUs
might have different default FontSubstitutes.

gfx/thebes/StandardFonts-win10.inc

@@ -200,3 +200,68 @@ static const char* kLangPackFonts[] = {
 //  "Rockwell Nova",  // Pan-European Supplemental Fonts - EXCLUDED
 //  "Verdana Pro",  // Pan-European Supplemental Fonts - EXCLUDED
 };
+
+struct FontSubstitute {
+  const char *substituteName;
+  const char *actualFontName;
+};
+
+static const FontSubstitute kFontSubstitutes[] = {
+  // Common substitutions
+  {"Arabic Transparent", "Arial"},
+  {"Arabic Transparent Bold", "Arial Bold"},
+  {"Arial Baltic", "Arial"},
+  {"Arial CE", "Arial"},
+  {"Arial CYR", "Arial"},
+  {"Arial Greek", "Arial"},
+  {"Arial TUR", "Arial"},
+  {"Courier New Baltic", "Courier New"},
+  {"Courier New CE", "Courier New"},
+  {"Courier New CYR", "Courier New"},
+  {"Courier New Greek", "Courier New"},
+  {"Courier New TUR", "Courier New"},
+  {"Helv", "MS Sans Serif"},
+  {"Helvetica", "Arial"},
+  {"MS Shell Dlg 2", "Tahoma"},
+  {"Tahoma Armenian", "Tahoma"},
+  {"Times", "Times New Roman"},
+  {"Times New Roman Baltic", "Times New Roman"},
+  {"Times New Roman CE", "Times New Roman"},
+  {"Times New Roman CYR", "Times New Roman"},
+  {"Times New Roman Greek", "Times New Roman"},
+  {"Times New Roman TUR", "Times New Roman"},
+  {"Tms Rmn", "MS Serif"},
+  // Common, except Japanese (which uses MS UI Gothic, instead)
+  {"MS Shell Dlg", "Microsoft Sans Serif"},
+  // Arabic
+  {"Arial (Arabic)", "Arial"},
+  {"Courier New (Arabic)", "Courier New"},
+  {"Times New Roman (Arabic)", "Times New Roman"},
+  // Cyrillic + Greek
+  {"Courier", "Courier New"},
+  // Greek
+  {"Fixedsys Greek", "Fixedsys"},
+  {"MS Serif Greek", "MS Serif"},
+  {"MS Sans Serif Greek", "MS Sans Serif"},
+  {"Small Fonts Greek", "Small Fonts"},
+  {"System Greek", "System"},
+  // Hebrew
+  {"Arial (Hebrew)", "Arial"},
+  {"Courier New (Hebrew)", "Courier New"},
+  {"David Transparent", "David"},
+  {"Fixed Miriam Transparent", "Miriam Fixed"},
+  {"Miriam Transparent", "Miriam"},
+  {"Rod Transparent", "Rod"},
+  {"Times New Roman (Hebrew)", "Times New Roman"},
+  // Japanese
+  {"標準明朝", "ＭＳ 明朝"},
+  {"標準ゴシック", "ＭＳ ゴシック"},
+  {"ゴシック", "ＭＳ ゴシック"},
+  {"ｺﾞｼｯｸ", "ＭＳ ゴシック"},
+  {"ｸｰﾘｴ", "Courier"},
+  {"ﾀｲﾑｽﾞﾛﾏﾝ", "Times New Roman"},
+  {"ﾍﾙﾍﾞﾁｶ", "Arial"},
+  // Simplified Chinese
+  {"FangSong_GB2312", "FangSong"},
+  {"KaiTi_GB2312", "KaiTi"},
+};

gfx/thebes/gfxDWriteFontList.cpp

@@ -1953,6 +1953,20 @@ static void RemoveCharsetFromFontSubstitute(nsACString& aName) {
 #define MAX_VALUE_DATA 512
 
 nsresult gfxDWriteFontList::GetFontSubstitutes() {
+  if (nsContentUtils::ShouldResistFingerprinting(
+          "Ignore any fingerprintable user font customization and normalize "
+          "font substitutes across different Windows SKUs.",
+          RFPTarget::FontVisibilityLangPack)) {
+    for (const FontSubstitute& fs : kFontSubstitutes) {
+      nsAutoCString substituteName(fs.substituteName);
+      nsAutoCString actualFontName(fs.actualFontName);
+      BuildKeyNameFromFontName(substituteName);
+      BuildKeyNameFromFontName(actualFontName);
+      AddSubstitute(substituteName, actualFontName);
+    }
+    return NS_OK;
+  }
+
   HKEY hKey;
   DWORD i, rv, lenAlias, lenActual, valueType;
   WCHAR aliasName[MAX_VALUE_NAME];
@@ -1987,15 +2001,24 @@ nsresult gfxDWriteFontList::GetFontSubstitutes() {
     BuildKeyNameFromFontName(substituteName);
     RemoveCharsetFromFontSubstitute(actualFontName);
     BuildKeyNameFromFontName(actualFontName);
+    AddSubstitute(substituteName, actualFontName);
+  }
+
+  return NS_OK;
+}
+
+void gfxDWriteFontList::AddSubstitute(const nsCString& substituteName,
+                                      const nsCString& actualFontName) {
   if (SharedFontList()) {
-      // Skip substitution if the original font is available, unless the option
-      // to apply substitutions unconditionally is enabled.
+    // Skip substitution if the original font is available, unless the
+    // option to apply substitutions unconditionally is enabled.
     if (!StaticPrefs::gfx_windows_font_substitutes_always_AtStartup()) {
-        // Font substitutions are recorded for the canonical family names; we
-        // don't need FindFamily to consider localized aliases when searching.
+      // Font substitutions are recorded for the canonical family names;
+      // we don't need FindFamily to consider localized aliases when
+      // searching.
       if (SharedFontList()->FindFamily(substituteName,
                                        /*aPrimaryNameOnly*/ true)) {
-          continue;
+        return;
       }
     }
     if (SharedFontList()->FindFamily(actualFontName,
@@ -2019,8 +2042,6 @@ nsresult gfxDWriteFontList::GetFontSubstitutes() {
     }
   }
 }
-  return NS_OK;
-}
 
 struct FontSubstitution {
   const char* aliasName;

gfx/thebes/gfxDWriteFontList.h

@@ -457,6 +457,9 @@ class gfxDWriteFontList final : public gfxPlatformFontList {
       const nsTArray<nsCString>* aForceClassicFams = nullptr)
       MOZ_REQUIRES(mLock);
 
+  void AddSubstitute(const nsCString& substituteName,
+                     const nsCString& actualFontName);
+
 #ifdef MOZ_BUNDLED_FONTS
   already_AddRefed<IDWriteFontCollection> CreateBundledFontsCollection(
       IDWriteFactory* aFactory);

gfx/thebes/gfxGDIFontList.cpp

@@ -31,6 +31,10 @@
 #include "mozilla/StaticPrefs_gfx.h"
 #include "mozilla/Telemetry.h"
 
+#include "nsContentUtils.h"
+
+#include "StandardFonts-win10.inc"
+
 #include <usp10.h>
 
 using namespace mozilla;
@@ -50,6 +54,10 @@ static __inline void BuildKeyNameFromFontName(nsAString& aName) {
   if (aName.Length() >= LF_FACESIZE) aName.Truncate(LF_FACESIZE - 1);
   ToLowerCase(aName);
 }
+static __inline void BuildKeyNameFromFontName(nsACString& aName) {
+  if (aName.Length() >= LF_FACESIZE) aName.Truncate(LF_FACESIZE - 1);
+  ToLowerCase(aName);
+}
 
 // Implementation of gfxPlatformFontList for Win32 GDI,
 // using GDI font enumeration APIs to get the list of fonts
@@ -529,6 +537,26 @@ static void RemoveCharsetFromFontSubstitute(nsAString& aName) {
 #define MAX_VALUE_DATA 512
 
 nsresult gfxGDIFontList::GetFontSubstitutes() {
+  if (nsContentUtils::ShouldResistFingerprinting(
+          "Ignore any fingerprintable user font customization and normalize "
+          "font substitutes across different Windows SKUs.",
+          RFPTarget::FontVisibilityLangPack)) {
+    for (const FontSubstitute& fs : kFontSubstitutes) {
+      nsAutoCString substituteName(fs.substituteName);
+      nsAutoCString actualFontName(fs.actualFontName);
+      BuildKeyNameFromFontName(substituteName);
+      BuildKeyNameFromFontName(actualFontName);
+      gfxFontFamily* ff;
+      if (!actualFontName.IsEmpty() &&
+          (ff = mFontFamilies.GetWeak(actualFontName))) {
+        mFontSubstitutes.InsertOrUpdate(substituteName, RefPtr{ff});
+      } else {
+        mNonExistingFonts.AppendElement(substituteName);
+      }
+    }
+    return NS_OK;
+  }
+
   HKEY hKey;
   DWORD i, rv, lenAlias, lenActual, valueType;
   WCHAR aliasName[MAX_VALUE_NAME];