Issue #1825952 by Fabianx, joelpittet, bdragon, heddn, chx, xjm, pwolanin,...

Issue #1825952 by Fabianx, joelpittet, bdragon, heddn, chx, xjm, pwolanin, mikey_p, ti2m, bfr, dags, cilefen, scor, mgifford: Turn on twig autoescape by default

core/includes/batch.inc

@@ -14,6 +14,7 @@
  * @see batch_get()
  */
 
+use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Component\Utility\Timer;
 use Drupal\Core\Batch\Percentage;
 use Drupal\Core\Page\DefaultHtmlPageRenderer;
@@ -44,7 +45,12 @@ function _batch_page(Request $request) {
       return new RedirectResponse(url('<front>', array('absolute' => TRUE)));
     }
   }
-
+  // Restore safe strings from previous batches.
+  // @todo Ensure we are not storing an excessively large string list in:
+  //   https://www.drupal.org/node/2295823
+  if (!empty($batch['safe_strings'])) {
+    SafeMarkup::setMultiple($batch['safe_strings']);
+  }
   // Register database update for the end of processing.
   drupal_register_shutdown_function('_batch_shutdown');
 
@@ -481,6 +487,10 @@ function _batch_finished() {
  */
 function _batch_shutdown() {
   if ($batch = batch_get()) {
+    // Update safe strings.
+    // @todo Ensure we are not storing an excessively large string list in:
+    //   https://www.drupal.org/node/2295823
+    $batch['safe_strings'] = SafeMarkup::getAll();
     \Drupal::service('batch.storage')->update($batch);
   }
 }

core/includes/bootstrap.inc

@@ -7,6 +7,7 @@
 use Drupal\Component\Datetime\DateTimePlus;
 use Drupal\Component\Utility\Crypt;
 use Drupal\Component\Utility\Environment;
+use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Component\Utility\String;
 use Drupal\Component\Utility\Unicode;
 use Drupal\Core\DrupalKernel;
@@ -888,8 +889,27 @@ function watchdog($type, $message, array $variables = array(), $severity = WATCH
  *
  * @return array|null
  *   A multidimensional array with keys corresponding to the set message types.
- *   The indexed array values of each contain the set messages for that type.
- *   Or, if there are no messages set, the function returns NULL.
+ *   The indexed array values of each contain the set messages for that type,
+ *   and each message is an associative array with the following format:
+ *   - safe: Boolean indicating whether the message string has been marked as
+ *     safe. Non-safe strings will be escaped automatically.
+ *   - message: The message string.
+ *   So, the following is an example of the full return array structure:
+ *   @code
+ *     array(
+ *       'status' => array(
+ *         array(
+ *           'safe' => TRUE,
+ *           'message' => 'A <em>safe</em> markup string.',
+ *         ),
+ *         array(
+ *           'safe' => FALSE,
+ *           'message' => "$arbitrary_user_input to escape.",
+ *         ),
+ *       ),
+ *     );
+ *   @endcode
+ *   If there are no messages set, the function returns NULL.
  *
  * @see drupal_get_messages()
  * @see theme_status_messages()
@@ -901,7 +921,10 @@ function drupal_set_message($message = NULL, $type = 'status', $repeat = FALSE)
     }
 
     if ($repeat || !in_array($message, $_SESSION['messages'][$type])) {
-      $_SESSION['messages'][$type][] = $message;
+      $_SESSION['messages'][$type][] = array(
+        'safe' => SafeMarkup::isSafe($message),
+        'message' => $message,
+      );
     }
 
     // Mark this page as being uncacheable.
@@ -928,17 +951,25 @@ function drupal_set_message($message = NULL, $type = 'status', $repeat = FALSE)
  *   intact. Defaults to TRUE.
  *
  * @return array
- *   A multidimensional array with keys corresponding to the set message types.
- *   The indexed array values of each contain the set messages for that type.
- *   The messages returned are limited to the type specified in the $type
- *   parameter. If there are no messages of the specified type, an empty array
- *   is returned.
+ *   An associative, nested array of messages grouped by message type, with
+ *   the top-level keys as the message type. The messages returned are
+ *   limited to the type specified in the $type parameter, if any. If there
+ *   are no messages of the specified type, an empty array is returned. See
+ *   drupal_set_message() for the array structure of indivdual messages.
  *
  * @see drupal_set_message()
  * @see theme_status_messages()
  */
 function drupal_get_messages($type = NULL, $clear_queue = TRUE) {
   if ($messages = drupal_set_message()) {
+    foreach ($messages as $message_type => $message_typed_messages) {
+      foreach ($message_typed_messages as $key => $message) {
+        if ($message['safe']) {
+          $message['message'] = SafeMarkup::set($message['message']);
+        }
+        $messages[$message_type][$key] = $message['message'];
+      }
+    }
     if ($type) {
       if ($clear_queue) {
         unset($_SESSION['messages'][$type]);

core/includes/common.inc

@@ -14,6 +14,7 @@
 use Drupal\Component\Utility\Bytes;
 use Drupal\Component\Utility\Crypt;
 use Drupal\Component\Utility\Number;
+use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Component\Utility\SortArray;
 use Drupal\Component\Utility\String;
 use Drupal\Component\Utility\Tags;
@@ -442,11 +443,15 @@ function format_rss_item($title, $link, $description, $args = array()) {
 /**
  * Formats XML elements.
  *
+ * Note: It is the caller's responsibility to sanitize any input parameters.
+ * This function does not perform sanitization.
+ *
  * @param $array
  *   An array where each item represents an element and is either a:
  *   - (key => value) pair (<key>value</key>)
  *   - Associative array with fields:
- *     - 'key': element name
+ *     - 'key': The element name. Element names are not sanitized, so do not
+ *       pass user input.
  *     - 'value': element contents
  *     - 'attributes': associative array of element attributes
  *
@@ -475,7 +480,11 @@ function format_xml_elements($array) {
       $output .= ' <' . $key . '>' . (is_array($value) ? format_xml_elements($value) : String::checkPlain($value)) . "</$key>\n";
     }
   }
-  return $output;
+  // @todo This is marking the output string as safe HTML, but we have only
+  //   sanitized the attributes and tag values, not the tag names, and we
+  //   cannot guarantee the assembled markup is safe. Consider a fix in:
+  //   https://www.drupal.org/node/2296885
+  return SafeMarkup::set($output);
 }
 
 /**
@@ -859,8 +868,7 @@ function l($text, $path, array $options = array()) {
 
   // Sanitize the link text if necessary.
   $text = $variables['options']['html'] ? $variables['text'] : String::checkPlain($variables['text']);
-
-  return '<a href="' . $url . '"' . $attributes . '>' . $text . '</a>';
+  return SafeMarkup::set('<a href="' . $url . '"' . $attributes . '>' . $text . '</a>');
 }
 
 /**
@@ -2640,12 +2648,17 @@ function drupal_pre_render_conditional_comments($elements) {
 /**
  * Pre-render callback: Renders a generic HTML tag with attributes into #markup.
  *
+ * Note: It is the caller's responsibility to sanitize any input parameters.
+ * This callback does not perform sanitization.
+ *
  * @param array $element
  *   An associative array containing:
  *   - #tag: The tag name to output. Typical tags added to the HTML HEAD:
  *     - meta: To provide meta information, such as a page refresh.
  *     - link: To refer to stylesheets and other contextual information.
  *     - script: To load JavaScript.
+ *     The value of #tag is not escaped or sanitized, so do not pass in user
+ *     input.
  *   - #attributes: (optional) An array of HTML attributes to apply to the
  *     tag.
  *   - #value: (optional) A string containing tag content, such as inline
@@ -2658,7 +2671,11 @@ function drupal_pre_render_conditional_comments($elements) {
 function drupal_pre_render_html_tag($element) {
   $attributes = isset($element['#attributes']) ? new Attribute($element['#attributes']) : '';
   if (!isset($element['#value'])) {
-    $markup = '<' . $element['#tag'] . $attributes . " />\n";
+    // This function is intended for internal use, so we assume that no unsafe
+    // values are passed in #tag. The attributes are already safe because
+    // Attribute output is already automatically sanitized.
+    // @todo Escape this properly instead? https://www.drupal.org/node/2296101
+    $markup = SafeMarkup::set('<' . $element['#tag'] . $attributes . " />\n");
   }
   else {
     $markup = '<' . $element['#tag'] . $attributes . '>';
@@ -2670,6 +2687,9 @@ function drupal_pre_render_html_tag($element) {
       $markup .= $element['#value_suffix'];
     }
     $markup .= '</' . $element['#tag'] . ">\n";
+    // @todo We cannot actually guarantee this markup is safe. Consider a fix
+    //   in: https://www.drupal.org/node/2296101
+    $markup = SafeMarkup::set($markup);
   }
   if (!empty($element['#noscript'])) {
     $element['#markup'] = '<noscript>' . $markup . '</noscript>';
@@ -3109,6 +3129,7 @@ function drupal_render(&$elements, $is_recursive_call = FALSE) {
       if (!$is_recursive_call) {
         _drupal_render_process_post_render_cache($elements);
       }
+      $elements['#markup'] = SafeMarkup::set($elements['#markup']);
       return $elements['#markup'];
     }
   }
@@ -3161,6 +3182,11 @@ function drupal_render(&$elements, $is_recursive_call = FALSE) {
     $elements['#children'] = '';
   }
 
+  // @todo Simplify after https://drupal.org/node/2273925
+  if (isset($elements['#markup'])) {
+    $elements['#markup'] = SafeMarkup::set($elements['#markup']);
+  }
+
   // Assume that if #theme is set it represents an implemented hook.
   $theme_is_implemented = isset($elements['#theme']);
 
@@ -3184,6 +3210,7 @@ function drupal_render(&$elements, $is_recursive_call = FALSE) {
     foreach ($children as $key) {
       $elements['#children'] .= drupal_render($elements[$key], TRUE);
     }
+    $elements['#children'] = SafeMarkup::set($elements['#children']);
   }
 
   // If #theme is not implemented and the element has raw #markup as a
@@ -3194,7 +3221,7 @@ function drupal_render(&$elements, $is_recursive_call = FALSE) {
   // required. Eventually #theme_wrappers will expect both #markup and
   // #children to be a single string as #children.
   if (!$theme_is_implemented && isset($elements['#markup'])) {
-    $elements['#children'] = $elements['#markup'] . $elements['#children'];
+    $elements['#children'] = SafeMarkup::set($elements['#markup'] . $elements['#children']);
   }
 
   // Let the theme functions in #theme_wrappers add markup around the rendered
@@ -3284,6 +3311,7 @@ function drupal_render(&$elements, $is_recursive_call = FALSE) {
   }
 
   $elements['#printed'] = TRUE;
+  $elements['#markup'] = SafeMarkup::set($elements['#markup']);
   return $elements['#markup'];
 }
 
@@ -3311,7 +3339,7 @@ function drupal_render_children(&$element, $children_keys = NULL) {
       $output .= drupal_render($element[$key]);
     }
   }
-  return $output;
+  return SafeMarkup::set($output);
 }
 
 /**

core/includes/errors.inc

@@ -5,10 +5,10 @@
  * Functions for error handling.
  */
 
+use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Page\DefaultHtmlPageRenderer;
 use Drupal\Core\Utility\Error;
-use Drupal\Component\Utility\String;
 use Symfony\Component\HttpFoundation\Response;
 
 /**
@@ -212,7 +212,7 @@ function _drupal_log_error($error, $fatal = FALSE) {
         // Generate a backtrace containing only scalar argument values.
         $message .= '<pre class="backtrace">' . Error::formatBacktrace($backtrace) . '</pre>';
       }
-      drupal_set_message($message, $class, TRUE);
+      drupal_set_message(SafeMarkup::set($message), $class, TRUE);
     }
 
     if ($fatal) {

core/includes/form.inc

@@ -7,6 +7,7 @@
 
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Component\Utility\Number;
+use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Component\Utility\String;
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Component\Utility\Xss;
@@ -907,7 +908,7 @@ function form_select_options($element, $choices = NULL) {
       $options .= '<option value="' . String::checkPlain($key) . '"' . $selected . '>' . String::checkPlain($choice) . '</option>';
     }
   }
-  return $options;
+  return SafeMarkup::set($options);
 }
 
 /**
@@ -1575,7 +1576,7 @@ function theme_tableselect($variables) {
           // A header can span over multiple cells and in this case the cells
           // are passed in an array. The order of this array determines the
           // order in which they are added.
-          if (!isset($element['#options'][$key][$fieldname]['data']) && is_array($element['#options'][$key][$fieldname])) {
+          if (is_array($element['#options'][$key][$fieldname]) && !isset($element['#options'][$key][$fieldname]['data'])) {
             foreach ($element['#options'][$key][$fieldname] as $cell) {
               $row['data'][] = $cell;
             }
@@ -1921,13 +1922,13 @@ function form_process_machine_name($element, &$form_state) {
   $element['#machine_name']['suffix'] = '#' . $suffix_id;
 
   if ($element['#machine_name']['standalone']) {
-    $element['#suffix'] .= ' <small id="' . $suffix_id . '">&nbsp;</small>';
+    $element['#suffix'] = SafeMarkup::set($element['#suffix'] . ' <small id="' . $suffix_id . '">&nbsp;</small>');
   }
   else {
     // Append a field suffix to the source form element, which will contain
     // the live preview of the machine name.
     $source += array('#field_suffix' => '');
-    $source['#field_suffix'] .= ' <small id="' . $suffix_id . '">&nbsp;</small>';
+    $source['#field_suffix'] = SafeMarkup::set($source['#field_suffix'] . ' <small id="' . $suffix_id . '">&nbsp;</small>');
 
     $parents = array_merge($element['#machine_name']['source'], array('#field_suffix'));
     NestedArray::setValue($form_state['complete_form'], $parents, $source['#field_suffix']);
@@ -3104,6 +3105,8 @@ function _form_set_attributes(&$element, $class = array()) {
  *   - css: Array of paths to CSS files to be used on the progress page.
  *   - url_options: options passed to url() when constructing redirect URLs for
  *     the batch.
+ *   - safe_strings: Internal use only. Used to store and retrieve strings
+ *     marked as safe between requests.
  */
 function batch_set($batch_definition) {
   if ($batch_definition) {
@@ -3227,6 +3230,11 @@ function batch_process($redirect = NULL, $url = 'batch', $redirect_callback = NU
         $request->query->remove('destination');
       }
 
+      // Store safe strings.
+      // @todo Ensure we are not storing an excessively large string list in:
+      //   https://www.drupal.org/node/2295823
+      $batch['safe_strings'] = SafeMarkup::getAll();
+
       // Store the batch.
       \Drupal::service('batch.storage')->create($batch);
 

core/includes/install.core.inc

 <?php
 
+use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\DrupalKernel;
 use Drupal\Core\Config\BootstrapConfigStorageFactory;
@@ -1707,10 +1708,10 @@ function install_finished(&$install_state) {
   // @todo Temporary hack to satisfy PIFR.
   // @see https://drupal.org/node/1317548
   $pifr_assertion = '<span style="display: none;">Drupal installation complete</span>';
-
-  drupal_set_message(t('Congratulations, you installed @drupal!', array(
+  $success_message = t('Congratulations, you installed @drupal!', array(
     '@drupal' => drupal_install_profile_distribution_name(),
-  )) . $pifr_assertion);
+  ));
+  drupal_set_message(SafeMarkup::set($success_message . $pifr_assertion));
 }
 
 /**

core/includes/theme.inc

@@ -8,6 +8,7 @@
  * customized by user themes.
  */
 
+use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Component\Utility\String;
 use Drupal\Component\Utility\UrlHelper;
 use Drupal\Component\Utility\Xss;
@@ -584,7 +585,7 @@ function _theme($hook, $variables = array()) {
   $output = '';
   if (isset($info['function'])) {
     if (function_exists($info['function'])) {
-      $output = $info['function']($variables);
+      $output = SafeMarkup::set($info['function']($variables));
     }
   }
   else {
@@ -2003,7 +2004,7 @@ function template_preprocess_html(&$variables) {
   // Construct page title.
   if ($page->hasTitle()) {
     $head_title = array(
-      'title' => trim(strip_tags($page->getTitle())),
+      'title' => SafeMarkup::set(trim(strip_tags($page->getTitle()))),
       'name' => String::checkPlain($site_config->get('name')),
     );
   }
@@ -2023,7 +2024,13 @@ function template_preprocess_html(&$variables) {
   }
 
   $variables['head_title_array'] = $head_title;
-  $variables['head_title'] = implode(' | ', $head_title);
+  $output = '';
+  $separator = '';
+  foreach ($head_title as $item) {
+    $output .= $separator . SafeMarkup::escape($item);
+    $separator = ' | ';
+  }
+  $variables['head_title'] = SafeMarkup::set($output);
 
   // @todo Remove drupal_*_html_head() and refactor accordingly.
   $html_heads = drupal_get_html_head(FALSE);

core/includes/theme.maintenance.inc

@@ -110,6 +110,8 @@ function _drupal_maintenance_theme() {
  * @param $variables
  *   An associative array containing:
  *   - items: An associative array of maintenance tasks.
+ *     It's the caller's responsibility to ensure this array's items contain no
+ *     dangerous HTML such as SCRIPT tags.
  *   - active: The key for the currently active maintenance task.
  *
  * @ingroup themeable
@@ -187,6 +189,8 @@ function theme_authorize_report($variables) {
  * @param $variables
  *   An associative array containing:
  *   - message: The log message.
+ *     It's the caller's responsibility to ensure this string contains no
+ *     dangerous HTML such as SCRIPT tags.
  *   - success: A boolean indicating failure or success.
  *
  * @ingroup themeable

core/lib/Drupal/Component/Diff/Engine/HWLDFWordAccumulator.php

@@ -4,6 +4,7 @@
 
 use Drupal\Component\Utility\String;
 use Drupal\Component\Utility\Unicode;
+use Drupal\Component\Utility\SafeMarkup;
 
 /**
  *  Additions by Axel Boldt follow, partly taken from diff.php, phpwiki-1.3.3
@@ -46,7 +47,9 @@ protected function _flushGroup($new_tag) {
   protected function _flushLine($new_tag) {
     $this->_flushGroup($new_tag);
     if ($this->line != '') {
-      array_push($this->lines, $this->line);
+      // @todo This is probably not the right place to do this. To be
+      //   addressed in https://drupal.org/node/2280963
+      array_push($this->lines, SafeMarkup::set($this->line));
     }
     else {
       // make empty lines visible by inserting an NBSP

core/lib/Drupal/Component/Utility/SafeMarkup.php

+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Utility\SafeMarkup.
+ */
+
+namespace Drupal\Component\Utility;
+
+/**
+ * Manages known safe strings for rendering at the theme layer.
+ *
+ * The Twig theme engine autoescapes string variables in the template, so it
+ * is possible for a string of markup to become double-escaped. SafeMarkup
+ * provides a store for known safe strings and methods to manage them
+ * throughout the page request.
+ *
+ * Strings sanitized by String::checkPlain() or Xss::filter() are automatically
+ * marked safe, as are markup strings created from render arrays via
+ * drupal_render().
+ *
+ * This class should be limited to internal use only. Module developers should
+ * instead use the appropriate
+ * @link sanitization sanitization functions @endlink or the
+ * @link theme_render theme and render systems @endlink so that the output can
+ * can be themed, escaped, and altered properly.
+ *
+ * @see twig_drupal_escape_filter()
+ * @see twig_render_template()
+ * @see sanitization
+ * @see theme_render
+ */
+class SafeMarkup {
+
+  /**
+   * The list of safe strings.
+   *
+   * @var array
+   */
+  protected static $safeStrings = array();
+
+  /**
+   * Adds a string to a list of strings marked as secure.
+   *
+   * This method is for internal use. Do not use it to prevent escaping of
+   * markup; instead, use the appropriate
+   * @link sanitization sanitization functions @endlink or the
+   * @link theme_render theme and render systems @endlink so that the output
+   * can be themed, escaped, and altered properly.
+   *
+   * This marks strings as secure for the entire page render, not just the code
+   * or element that set it. Therefore, only valid HTML should be
+   * marked as safe (never partial markup). For example, you should never do:
+   * @code
+   *   SafeMarkup::set("<");
+   * @endcode
+   * or:
+   * @code
+   *   SafeMarkup::set('<script>');
+   * @endcode
+   *
+   * @param string $string
+   *   The content to be marked as secure.
+   * @param string $strategy
+   *   The escaping strategy used for this string. Two values are supported
+   *   by default:
+   *   - 'html': (default) The string is safe for use in HTML code.
+   *   - 'all': The string is safe for all use cases.
+   *   See the
+   *   @link http://twig.sensiolabs.org/doc/filters/escape.html Twig escape documentation @endlink
+   *   for more information on escaping strategies in Twig.
+   *
+   * @return string
+   *   The input string that was marked as safe.
+   */
+  public static function set($string, $strategy = 'html') {
+    $string = (string) $string;
+    static::$safeStrings[$string][$strategy] = TRUE;
+    return $string;
+  }
+
+  /**
+   * Checks if a string is safe to output.
+   *
+   * @param string $string
+   *   The content to be checked.
+   * @param string $strategy
+   *   The escaping strategy. See SafeMarkup::set(). Defaults to 'html'.
+   *
+   * @return bool
+   *   TRUE if the string has been marked secure, FALSE otherwise.
+   */
+  public static function isSafe($string, $strategy = 'html') {
+    return isset(static::$safeStrings[(string) $string][$strategy]) ||
+      isset(static::$safeStrings[(string) $string]['all']);
+  }
+
+  /**
+   * Adds previously retrieved known safe strings to the safe string list.
+   *
+   * This is useful for the batch and form APIs, where it is important to
+   * preserve the safe markup state across page requests. The strings will be
+   * added to any safe strings already marked for the current request.
+   *
+   * @param array $safe_strings
+   *   A list of safe strings as previously retrieved by SafeMarkup::getAll().
+   *
+   * @throws \UnexpectedValueException
+   */
+  public static function setMultiple(array $safe_strings) {
+    foreach ($safe_strings as $string => $strategies) {
+      foreach ($strategies as $strategy => $value) {
+        $string = (string) $string;
+        if ($value === TRUE) {
+          static::$safeStrings[$string][$strategy] = TRUE;
+        }
+        else {
+          // Danger - something is very wrong.
+          throw new \UnexpectedValueException('Only the value TRUE is accepted for safe strings');
+        }
+      }
+    }
+  }
+
+  /**
+   * Encodes special characters in a plain-text string for display as HTML.
+   *
+   * @param $string
+   *   A string.
+   *
+   * @return string
+   *   The escaped string. If $string was already set as safe with
+   *   SafeString::set, it won't be escaped again.
+   */
+  public static function escape($string) {
+    return static::isSafe($string) ? $string : String::checkPlain($string);
+  }
+
+  /**
+  * Retrieves all strings currently marked as safe.
+  *
+  * This is useful for the batch and form APIs, where it is important to
+  * preserve the safe markup state across page requests.
+  *
+  * @return array
+  *   Returns all strings currently marked safe.
+  */
+  public static function getAll() {
+    return static::$safeStrings;
+  }
+
+}

core/lib/Drupal/Component/Utility/String.php

@@ -17,7 +17,8 @@ class String {
   /**
    * Encodes special characters in a plain-text string for display as HTML.
    *
-   * Also validates strings as UTF-8.
+   * Also validates strings as UTF-8. All processed strings are also
+   * automatically flagged as safe markup strings for rendering.
    *
    * @param string $text
    *   The text to be checked or processed.
@@ -29,9 +30,10 @@ class String {
    * @ingroup sanitization
    *
    * @see drupal_validate_utf8()
+   * @see \Drupal\Component\Utility\SafeMarkup
    */
   public static function checkPlain($text) {
-    return htmlspecialchars($text, ENT_QUOTES, 'UTF-8');
+    return SafeMarkup::set(htmlspecialchars($text, ENT_QUOTES, 'UTF-8'));
   }
 
   /**
@@ -65,7 +67,8 @@ public static function decodeEntities($text) {
    * addition to formatting it.
    *
    * @param $string
-   *   A string containing placeholders.
+   *   A string containing placeholders. The string itself is not escaped, any
+   *   unsafe content must be in $args and inserted via placeholders.
    * @param $args
    *   An associative array of replacements to make. Occurrences in $string of
    *   any key in $args are replaced with the corresponding value, after
@@ -111,7 +114,7 @@ public static function format($string, array $args = array()) {
           // Pass-through.
       }
     }
-    return strtr($string, $args);
+    return SafeMarkup::set(strtr($string, $args));
   }
 
   /**
@@ -126,7 +129,8 @@ public static function format($string, array $args = array()) {
    *   The formatted text (html).
    */
   public static function placeholder($text) {
-    return '<em class="placeholder">' . static::checkPlain($text) . '</em>';
+    return SafeMarkup::set('<em class="placeholder">' . static::checkPlain($text) . '</em>');
   }
 
+
 }

core/lib/Drupal/Component/Utility/Xss.php

@@ -41,12 +41,14 @@ class Xss {
    * Based on kses by Ulf Harnhammar, see http://sourceforge.net/projects/kses.
    * For examples of various XSS attacks, see: http://ha.ckers.org/xss.html.
    *
-   * This code does four things:
+   * This code does five things:
    * - Removes characters and constructs that can trick browsers.
    * - Makes sure all HTML entities are well-formed.
    * - Makes sure all HTML tags and attributes are well-formed.
    * - Makes sure no HTML tags contain URLs with a disallowed protocol (e.g.
    *   javascript:).
+   * - Marks the sanitized, XSS-safe version of $string as safe markup for
+   *   rendering.
    *
    * @param $string
    *   The string with raw HTML in it. It will be stripped of everything that
@@ -63,6 +65,7 @@ class Xss {
    *   valid UTF-8.
    *
    * @see \Drupal\Component\Utility\Unicode::validateUtf8()
+   * @see \Drupal\Component\Utility\SafeMarkup
    *
    * @ingroup sanitization
    */
@@ -90,7 +93,7 @@ public static function filter($string, $html_tags = array('a', 'em', 'strong', '
     $splitter = function ($matches) use ($html_tags, $mode) {
       return static::split($matches[1], $html_tags, $mode);
     };
-    return preg_replace_callback('%
+    return SafeMarkup::set(preg_replace_callback('%
       (
       <(?=[^a-zA-Z!/])  # a lone <
       |                 # or
@@ -99,7 +102,7 @@ public static function filter($string, $html_tags = array('a', 'em', 'strong', '
       <[^>]*(>|$)       # a string that starts with a <, up until the > or the end of the string
       |                 # or
       >                 # just a >
-      )%x', $splitter, $string);
+      )%x', $splitter, $string));
   }
 
   /**

core/lib/Drupal/Core/Controller/ExceptionController.php

@@ -17,6 +17,7 @@
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\HttpFoundation\JsonResponse;
 use Symfony\Component\HttpKernel\HttpKernelInterface;
+use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Component\Utility\String;
 use Symfony\Component\Debug\Exception\FlattenException;
 use Drupal\Core\ContentNegotiation;
@@ -316,7 +317,7 @@ public function on500Html(FlattenException $exception, Request $request) {
         // Generate a backtrace containing only scalar argument values.
         $message .= '<pre class="backtrace">' . Error::formatFlattenedBacktrace($backtrace) . '</pre>';
       }
-      drupal_set_message($message, $class, TRUE);
+      drupal_set_message(SafeMarkup::set($message), $class, TRUE);
     }
 
     $content = $this->t('The website has encountered an error. Please try again later.');

core/lib/Drupal/Core/CoreServiceProvider.php

@@ -90,9 +90,7 @@ public static function registerTwig(ContainerBuilder $container) {
         // When in the installer, twig_cache must be FALSE until we know the