[Mac] Modify the ObjC exception preprocessor to make some exceptions fatal.

chrome/browser/mac/exception_processor.mm

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "chrome/browser/mac/exception_processor.h"
+
+#import <Foundation/Foundation.h>
+#include <libunwind.h>
+#include <objc/objc-exception.h>
+
+#include <type_traits>
+
+#include "base/compiler_specific.h"
+#include "base/debug/crash_logging.h"
+#include "base/debug/stack_trace.h"
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/metrics/histogram_macros.h"
+#include "base/strings/sys_string_conversions.h"
+#include "chrome/common/crash_keys.h"
+
+namespace chrome {
+
+// Maximum number of known named exceptions we'll support.  There is
+// no central registration, but I only find about 75 possibilities in
+// the system frameworks, and many of them are probably not
+// interesting to track in aggregate (those relating to distributed
+// objects, for instance).
+constexpr size_t kKnownNSExceptionCount = 25;
+
+const size_t kUnknownNSException = kKnownNSExceptionCount;
+
+size_t BinForException(NSException* exception) {
+  // A list of common known exceptions.  The list position will
+  // determine where they live in the histogram, so never move them
+  // around, only add to the end.
+  NSString* const kKnownNSExceptionNames[] = {
+    // Grab-bag exception, not very common.  CFArray (or other
+    // container) mutated while being enumerated is one case seen in
+    // production.
+    NSGenericException,
+
+    // Out-of-range on NSString or NSArray.  Quite common.
+    NSRangeException,
+
+    // Invalid arg to method, unrecognized selector.  Quite common.
+    NSInvalidArgumentException,
+
+    // malloc() returned null in object creation, I think.  Turns out
+    // to be very uncommon in production, because of the OOM killer.
+    NSMallocException,
+
+    // This contains things like windowserver errors, trying to draw
+    // views which aren't in windows, unable to read nib files.  By
+    // far the most common exception seen on the crash server.
+    NSInternalInconsistencyException,
+  };
+
+  // Make sure our array hasn't outgrown our abilities to track it.
+  static_assert(arraysize(kKnownNSExceptionNames) < kKnownNSExceptionCount,
+                "Cannot track more exceptions");
+
+  NSString* name = [exception name];
+  for (size_t i = 0; i < arraysize(kKnownNSExceptionNames); ++i) {
+    if (name == kKnownNSExceptionNames[i]) {
+      return i;
+    }
+  }
+  return kUnknownNSException;
+}
+
+void RecordExceptionWithUma(NSException* exception) {
+  UMA_HISTOGRAM_ENUMERATION("OSX.NSException",
+      BinForException(exception), kUnknownNSException);
+}
+
+static objc_exception_preprocessor g_next_preprocessor = nullptr;
+
+static const char* const kExceptionSinkholes[] = {
+  "CFRunLoopRunSpecific",
+  "_dispatch_client_callout",
+};
+
+// This function is used to make it clear to the crash processor that this is
+// a forced exception crash.
+static NOINLINE void TERMINATING_FROM_UNCAUGHT_NSEXCEPTION(id exception) {
+  LOG(FATAL) << "Terminating from Objective-C exception: "
+             << base::SysNSStringToUTF8([exception name])
+             << ": " << base::SysNSStringToUTF8([exception reason]);
+}
+
+static id ObjcExceptionPreprocessor(id exception) {
+  static bool seen_first_exception = false;
+
+  // Record UMA and crash keys about the exception.
+  RecordExceptionWithUma(exception);
+
+  const char* const kExceptionKey =
+      seen_first_exception ? crash_keys::mac::kLastNSException
+                           : crash_keys::mac::kFirstNSException;
+  NSString* value = [NSString stringWithFormat:@"%@ reason %@",
+      [exception name], [exception reason]];
+  base::debug::SetCrashKeyValue(kExceptionKey, base::SysNSStringToUTF8(value));
+
+  const char* const kExceptionTraceKey =
+      seen_first_exception ? crash_keys::mac::kLastNSExceptionTrace
+                           : crash_keys::mac::kFirstNSExceptionTrace;
+  // This exception preprocessor runs prior to the one in libobjc, which sets
+  // the -[NSException callStackReturnAddresses].
+  base::debug::SetCrashKeyToStackTrace(kExceptionTraceKey,
+                                       base::debug::StackTrace());
+
+  seen_first_exception = true;
+
+  //////////////////////////////////////////////////////////////////////////////
+
+  // Unwind the stack looking for any exception handlers. If an exception
+  // handler is encountered, test to see if it is a function known to catch-
+  // and-rethrow as a "top-level" exception handler. Various routines in
+  // Cocoa do this, and it obscures the crashing stack, since the original
+  // throw location is no longer present on the stack (just the re-throw) when
+  // Crashpad captures the crash report.
+  unw_context_t context;
+  unw_getcontext(&context);
+
+  unw_cursor_t cursor;
+  unw_init_local(&cursor, &context);
+
+  while (unw_step(&cursor) > 0) {
+    unw_proc_info_t frame_info;
+    if (unw_get_proc_info(&cursor, &frame_info) != UNW_ESUCCESS) {
+      continue;
+    }
+
+    // This frame has an exception handler.
+    if (frame_info.handler != 0) {
+      char proc_name[64];
+      unw_word_t offset;
+      if (unw_get_proc_name(&cursor, proc_name, sizeof(proc_name),
+                            &offset) != UNW_ESUCCESS) {
+        continue;
+      }
+
+      // Check if the function is one that is known to obscure (by way of
+      // catch-and-rethrow) exception stack traces. If it is, sinkhole it
+      // by crashing here at the point of throw.
+      for (const auto& sinkhole : kExceptionSinkholes) {
+        if (strcmp(sinkhole, proc_name) == 0) {
+          TERMINATING_FROM_UNCAUGHT_NSEXCEPTION(exception);
+        }
+      }
+
+      break;
+    }
+  }
+
+  // Forward to the next preprocessor.
+  if (g_next_preprocessor)
+    return g_next_preprocessor(exception);
+
+  return exception;
+}
+
+void InstallObjcExceptionPreprocessor() {
+  if (g_next_preprocessor)
+    return;
+
+  g_next_preprocessor =
+      objc_setExceptionPreprocessor(&ObjcExceptionPreprocessor);
+}
+
+void UninstallObjcExceptionPreprocessor() {
+  objc_setExceptionPreprocessor(g_next_preprocessor);
+  g_next_preprocessor = nullptr;
+}
+
+}  // namespace chrome