Accept non-fatal resource exceptions without generating crash reports

util/mach/exception_types.cc

Index: util/mach/exception_types.cc
diff --git a/util/mach/exception_types.cc b/util/mach/exception_types.cc
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+// Copyright 2015 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "util/mach/exception_types.h"
+
+#include <Availability.h>
+#include <AvailabilityMacros.h>
+#include <dlfcn.h>
+#include <errno.h>
+#include <libproc.h>
+#include <kern/exc_resource.h>
+
+#include "base/logging.h"
+#include "base/mac/mach_logging.h"
+#include "util/mac/mac_util.h"
+
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_9
+
+extern "C" {
+
+// proc_get_wakemon_params() is present in the Mac OS X 10.9 SDK, but no
+// declaration is provided. This provides a declaration and marks it for weak
+// import if the deployment target is below 10.9.
+int proc_get_wakemon_params(pid_t pid, int* rate_hz, int* flags)
+    __OSX_AVAILABLE_STARTING(__MAC_10_9, __IPHONE_7_0);
+
+}  // extern "C"
+
+#else
+
+namespace {
+
+using ProcGetWakemonParamsType = int (*)(pid_t, int*, int*);
+
+// The SDK doesn’t have proc_get_wakemon_params() to link against, even with
+// weak import. This function returns a function pointer to it if it exists at
+// runtime, or nullptr if it doesn’t. proc_get_wakemon_params() is looked up in
+// the same module that provides proc_pidinfo().
+ProcGetWakemonParamsType GetProcGetWakemonParams() {
+  Dl_info dl_info;
+  if (!dladdr(reinterpret_cast<void*>(proc_pidinfo), &dl_info)) {
+    return nullptr;
+  }
+
+  void* dl_handle =
+      dlopen(dl_info.dli_fname, RTLD_LAZY | RTLD_LOCAL | RTLD_NOLOAD);
+  if (!dl_handle) {
+    return nullptr;
+  }
+
+  ProcGetWakemonParamsType proc_get_wakemon_params =
+      reinterpret_cast<ProcGetWakemonParamsType>(
+          dlsym(dl_handle, "proc_get_wakemon_params"));
+  return proc_get_wakemon_params;
+}
+
+}  // namespace
+
+#endif
+
+namespace {
+
+// Wraps proc_get_wakemon_params(), calling it if the system provides it. It’s
+// present on Mac OS X 10.9 and later. If it’s not available, sets errno to
+// ENOSYS and returns -1.
+int ProcGetWakemonParams(pid_t pid, int* rate_hz, int* flags) {
+#if MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_9
+  // proc_get_wakemon_params() isn’t in the SDK. Look it up dynamically.
+  static ProcGetWakemonParamsType proc_get_wakemon_params =
+      GetProcGetWakemonParams();
+#endif
+
+#if MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_9
+  // proc_get_wakemon_params() is definitely available if the deployment target
+  // is 10.9 or newer.
+  if (!proc_get_wakemon_params) {
+    errno = ENOSYS;
+    return -1;
+  }
+#endif
+
+  return proc_get_wakemon_params(pid, rate_hz, flags);
+}
+
+}  // namespace
+
+namespace crashpad {
+
+exception_type_t ExcCrashRecoverOriginalException(
+    mach_exception_code_t code_0,
+    mach_exception_code_t* original_code_0,
+    int* signal) {
+  // 10.9.4 xnu-2422.110.17/bsd/kern/kern_exit.c proc_prepareexit() sets code[0]
+  // based on the signal value, original exception type, and low 20 bits of the
+  // original code[0] before calling xnu-2422.110.17/osfmk/kern/exception.c
+  // task_exception_notify() to raise an EXC_CRASH.
+  //
+  // The list of core-generating signals (as used in proc_prepareexit()’s call
+  // to hassigprop()) is in 10.9.4 xnu-2422.110.17/bsd/sys/signalvar.h sigprop:
+  // entires with SA_CORE are in the set. These signals are SIGQUIT, SIGILL,
+  // SIGTRAP, SIGABRT, SIGEMT, SIGFPE, SIGBUS, SIGSEGV, and SIGSYS. Processes
+  // killed for code-signing reasons will be killed by SIGKILL and are also
+  // eligible for EXC_CRASH handling, but processes killed by SIGKILL for other
+  // reasons are not.
+  if (signal) {
+    *signal = (code_0 >> 24) & 0xff;
+  }
+
+  if (original_code_0) {
+    *original_code_0 = code_0 & 0xfffff;
+  }
+
+  return (code_0 >> 20) & 0xf;
+}
+
+bool IsExceptionNonfatalResource(exception_type_t exception,
+                                 mach_exception_code_t code_0,
+                                 pid_t pid) {
+  if (exception != EXC_RESOURCE) {
+    return false;
+  }
+
+  const int resource_type = EXC_RESOURCE_DECODE_RESOURCE_TYPE(code_0);
+  const int resource_flavor = EXC_RESOURCE_DECODE_FLAVOR(code_0);
+
+  if (resource_type == RESOURCE_TYPE_CPU &&
+      (resource_flavor == FLAVOR_CPU_MONITOR ||
+       resource_flavor == FLAVOR_CPU_MONITOR_FATAL)) {
+    // These exceptions may be fatal. They are not fatal by default at task
+    // creation but can be made fatal by calling proc_rlimit_control() with
+    // RLIMIT_CPU_USAGE_MONITOR as the second argument and CPUMON_MAKE_FATAL set
+    // in the flags.
+    if (MacOSXMinorVersion() >= 10) {
+      // In Mac OS X 10.10, the exception code indicates whether the exception
+      // is fatal. See 10.10 xnu-2782.1.97/osfmk/kern/thread.c
+      // THIS_THREAD_IS_CONSUMING_TOO_MUCH_CPU__SENDING_EXC_RESOURCE().
+      return resource_flavor == FLAVOR_CPU_MONITOR;
+    }
+
+    // In Mac OS X 10.9, there’s no way to determine whether the exception is
+    // fatal. Unlike RESOURCE_TYPE_WAKEUPS below, there’s no way to determine
+    // this outside the kernel. proc_rlimit_control()’s RLIMIT_CPU_USAGE_MONITOR
+    // is the only interface to modify CPUMON_MAKE_FATAL, but it’s only able to
+    // set this bit, not obtain its current value.
+    //
+    // Default to assuming that these exceptions are nonfatal. They are nonfatal
+    // by default and no users of proc_rlimit_control() were found on 10.9.5
+    // 13F1066 in /System and /usr outside of Metadata.framework and associated
+    // tools.
+    return true;
+  }
+
+  if (resource_type == RESOURCE_TYPE_WAKEUPS &&
+      resource_flavor == FLAVOR_WAKEUPS_MONITOR) {
+    // These exceptions may be fatal. They are not fatal by default at task
+    // creation, but can be made fatal by calling proc_rlimit_control() with
+    // RLIMIT_WAKEUPS_MONITOR as the second argument and WAKEMON_MAKE_FATAL set
+    // in the flags.
+    //
+    // proc_get_wakemon_params() (which calls
+    // through to proc_rlimit_control() with RLIMIT_WAKEUPS_MONITOR) determines
+    // whether these exceptions are fatal. See 10.10
+    // xnu-2782.1.97/osfmk/kern/task.c
+    // THIS_PROCESS_IS_CAUSING_TOO_MANY_WAKEUPS__SENDING_EXC_RESOURCE().
+    //
+    // If proc_get_wakemon_params() fails, default to assuming that these
+    // exceptions are nonfatal. They are nonfatal by default and no users of
+    // proc_rlimit_control() were found on 10.9.5 13F1066 in /System and /usr
+    // outside of Metadata.framework and associated tools.
+    int wm_rate;
+    int wm_flags;
+    int rv = ProcGetWakemonParams(pid, &wm_rate, &wm_flags);
+    if (rv < 0) {
+      PLOG(WARNING) << "ProcGetWakemonParams";
+      return true;
+    }
+
+    return !(wm_flags & WAKEMON_MAKE_FATAL);
+  }
+
+  if (resource_type == RESOURCE_TYPE_MEMORY &&
+      resource_flavor == FLAVOR_HIGH_WATERMARK) {
+    // These exceptions are never fatal. See 10.10
+    // xnu-2782.1.97/osfmk/kern/task.c
+    // THIS_PROCESS_CROSSED_HIGH_WATERMARK__SENDING_EXC_RESOURCE().
+    return true;
+  }
+
+  // Treat unknown exceptions as fatal. This is the conservative approach: it
+  // may result in more crash reports being generated, but the type-flavor
+  // combinations can be evaluated to determine appropriate handling.
+  LOG(WARNING) << "unknown resource type " << resource_type << " flavor "
+               << resource_flavor;
+  return false;
+}
+
+}  // namespace crashpad