[asan] Return allow_user_segv_handler=0 to fix compatibility issues.

[vitalybuka]

Summary

After r303941 it was not possible to setup ASAN_OPTIONS to have the same
behavior for pre r303941 and post r303941 builds.
Pre r303941 Asan does not accept handle_sigbus=2.
Post r303941 Asan does not accept allow_user_segv_handler.

This fix ignores allow_user_segv_handler=1, but for allow_user_segv_handler=0
it will upgrade flags like handle_sigbus=1 to handle_sigbus=2. So user can set
ASAN_OPTIONS=allow_user_segv_handler=0 and have same behavior on old and new
clang builds (except range from r303941 to this revision).

In future users which need to prevent third party handlers should switch to
handle_sigbus=2 and remove allow_user_segv_handler as soon as suport of older
builds is not needed.

Related bugs:

https://github.com/google/oss-fuzz/issues/675
https://bugs.chromium.org/p/chromium/issues/detail?id=731130

[vitalybuka]

Updated test

[eugenis]

LGTM

lib/sanitizer_common/sanitizer_flags.inc

COMMON_FLAG(HandleSignalMode, handle_sigbus, kHandleSignalYes,
             COMMON_FLAG_HANDLE_SIGNAL_HELP(SIGBUS))
 COMMON_FLAG(HandleSignalMode, handle_abort, kHandleSignalNo,
             COMMON_FLAG_HANDLE_SIGNAL_HELP(SIGABRT))
 COMMON_FLAG(HandleSignalMode, handle_sigill, kHandleSignalNo,
             COMMON_FLAG_HANDLE_SIGNAL_HELP(SIGILL))
 COMMON_FLAG(HandleSignalMode, handle_sigfpe, kHandleSignalYes,
             COMMON_FLAG_HANDLE_SIGNAL_HELP(SIGFPE))
 #undef COMMON_FLAG_HANDLE_SIGNAL_HELP
+COMMON_FLAG(bool, allow_user_segv_handler, true,
+            "Deprecated. Thue has no effect, see handle_sigbus. If false, "
+            "handle_*=1 will be upgraded to handle_*=2.")
 COMMON_FLAG(bool, use_sigaltstack, true,
             "If set, uses alternate stack for signal handling.")
 COMMON_FLAG(bool, detect_deadlocks, false,
             "If set, deadlock detection is enabled.")
 COMMON_FLAG(
     uptr, clear_shadow_mmap_threshold, 64 * 1024,
     "Large shadow regions are zero-filled using mmap(NORESERVE) instead of "
     "memset(). This is the threshold size in bytes.")

lib/sanitizer_common/sanitizer_linux.cc

AndroidApiLevel AndroidGetApiLevel() {
   if (level) return level;
   level = AndroidDetectApiLevel();
   atomic_store(&android_api_level, level, memory_order_relaxed);
   return level;
 }
 
 #endif
 
-HandleSignalMode GetHandleSignalMode(int signum) {
+static HandleSignalMode GetHandleSignalModeImpl(int signum) {
   switch (signum) {
     case SIGABRT:
       return common_flags()->handle_abort;
     case SIGILL:
       return common_flags()->handle_sigill;
     case SIGFPE:
       return common_flags()->handle_sigfpe;
     case SIGSEGV:
       return common_flags()->handle_segv;
     case SIGBUS:
       return common_flags()->handle_sigbus;
   }
   return kHandleSignalNo;
 }
 
+HandleSignalMode GetHandleSignalMode(int signum) {
+  HandleSignalMode result = GetHandleSignalModeImpl(signum);
+  if (result == kHandleSignalYes && !common_flags()->allow_user_segv_handler)
+    return kHandleSignalExclusive;
+  return result;
+}
+
 #if !SANITIZER_GO
 void *internal_start_thread(void(*func)(void *arg), void *arg) {
   // Start the thread with signals blocked, otherwise it can steal user signals.
   __sanitizer_sigset_t set, old;
   internal_sigfillset(&set);
 #if SANITIZER_LINUX && !SANITIZER_ANDROID
   // Glibc uses SIGSETXID signal during setuid call. If this signal is blocked
   // on any thread, setuid call hangs (see test/tsan/setuid.c).

lib/sanitizer_common/sanitizer_mac.cc

 }
 
 void ListOfModules::init() {
   clear();
   MemoryMappingLayout memory_mapping(false);
   memory_mapping.DumpListOfModules(&modules_);
 }
 
-HandleSignalMode GetHandleSignalMode(int signum) {
-  // Handling fatal signals on watchOS and tvOS devices is disallowed.
-  if ((SANITIZER_WATCHOS || SANITIZER_TVOS) && !(SANITIZER_IOSSIM))
-    return kHandleSignalNo;
+static HandleSignalMode GetHandleSignalModeImpl(int signum) {
   switch (signum) {
     case SIGABRT:
       return common_flags()->handle_abort;
     case SIGILL:
       return common_flags()->handle_sigill;
     case SIGFPE:
       return common_flags()->handle_sigfpe;
     case SIGSEGV:
       return common_flags()->handle_segv;
     case SIGBUS:
       return common_flags()->handle_sigbus;
   }
   return kHandleSignalNo;
 }
 
+HandleSignalMode GetHandleSignalMode(int signum) {
+  // Handling fatal signals on watchOS and tvOS devices is disallowed.
+  if ((SANITIZER_WATCHOS || SANITIZER_TVOS) && !(SANITIZER_IOSSIM))
+    return kHandleSignalNo;
+  HandleSignalMode result = GetHandleSignalModeImpl(signum);
+  if (result == kHandleSignalYes && !common_flags()->allow_user_segv_handler)
+    return kHandleSignalExclusive;
+  return result;
+}
+
 MacosVersion cached_macos_version = MACOS_VERSION_UNINITIALIZED;
 
 MacosVersion GetMacosVersionInternal() {
   int mib[2] = { CTL_KERN, KERN_OSRELEASE };
   char version[100];
   uptr len = 0, maxlen = sizeof(version) / sizeof(version[0]);
   for (uptr i = 0; i < maxlen; i++) version[i] = '\0';
   // Get the version length.

test/asan/TestCases/Posix/allow_user_segv.cc

 // Regression test for
 // https://code.google.com/p/address-sanitizer/issues/detail?id=180
 
 // RUN: %clangxx_asan -O0 %s -o %t && %env_asan_opts=handle_segv=0 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK0
 // RUN: %clangxx_asan -O2 %s -o %t && %env_asan_opts=handle_segv=0 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK0
 
 // RUN: %clangxx_asan -O0 %s -o %t && %env_asan_opts=handle_segv=1 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK1
 // RUN: %clangxx_asan -O2 %s -o %t && %env_asan_opts=handle_segv=1 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK1
 
 // RUN: %clangxx_asan -O0 %s -o %t && %env_asan_opts=handle_segv=2 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK2
 // RUN: %clangxx_asan -O2 %s -o %t && %env_asan_opts=handle_segv=2 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK2
 
+// RUN: %clangxx_asan -O0 %s -o %t && %env_asan_opts=handle_segv=0:allow_user_segv_handler=0 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK0
+// RUN: %clangxx_asan -O0 %s -o %t && %env_asan_opts=handle_segv=1:allow_user_segv_handler=0 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK2
+// RUN: %clangxx_asan -O0 %s -o %t && %env_asan_opts=handle_segv=2:allow_user_segv_handler=0 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK2
+
+// RUN: %clangxx_asan -O0 %s -o %t && %env_asan_opts=handle_segv=0:allow_user_segv_handler=1 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK0
+// RUN: %clangxx_asan -O0 %s -o %t && %env_asan_opts=handle_segv=1:allow_user_segv_handler=1 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK1
+// RUN: %clangxx_asan -O0 %s -o %t && %env_asan_opts=handle_segv=2:allow_user_segv_handler=1 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK2
+
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 
 struct sigaction original_sigaction_sigbus;
 struct sigaction original_sigaction_sigsegv;
 
 void User_OnSIGSEGV(int signum, siginfo_t *siginfo, void *context) {