[asan] Add OS X 10.11's new dyld interposition support

[kubamracek]

Summary

On OS X 10.11 (which is currently a public beta), the dynamic linker has been improved so that it doesn't require the use of DYLD_INSERT_LIBRARIES in order for interposition/wrappers to work. This patch adds support of this behavior into ASan – we no longer need to re-exec in case the env. variable is not set.

Since on older OS versions (10.10 and lower) we still need to keep the old behavior, this patch adds a runtime check for the OS version via GetMacosVersion. This turns out to be a little more complicated for the iOS Simulator, where this method reports the host's version and not the simulator's. Proper version checking via iOS system API is problematic to do this early in the process runtime. Instead, the patch contains a hack that checks presence of a symbol which is known to be available only on the newer system.

[samsonov]

LGTM

[kubamracek]

Landed in r241487.

[glider]

LGTM, sorry for the delay.

lib/asan/asan_mac.cc

104

This is great.

test/asan/TestCases/Darwin/dyld_insert_libraries_reexec.cc

15

Don't we run Darwin tests on the iOS simulator?

[kubamracek]

test/asan/TestCases/Darwin/dyld_insert_libraries_reexec.cc

15

I'm not aware of that. I don't think there is any easy (documented) way to execute command-line programs in iOS simulator.

lib/asan/asan_mac.cc

 }
 
 static bool reexec_disabled = false;
 
 void DisableReexec() {
   reexec_disabled = true;
 }
 
+bool DyldNeedsEnvVariable() {
+// If running on OS X 10.11+ or iOS 9.0+, dyld will interpose even if
+// DYLD_INSERT_LIBRARIES is not set.
+
+#if SANITIZER_IOSSIM
+  // GetMacosVersion will not work for the simulator, whose kernel version
+  // is tied to the host. Use a weak linking hack for the simulator.
+  // This API was introduced in the same version of the OS as the dyld
+  // optimization.
+
+  // Check for presence of a symbol that is available on OS X 10.11+, iOS 9.0+.
+  return (dlsym(RTLD_NEXT, "mach_memory_info") == nullptr);
+#else
+  return (GetMacosVersion() <= MACOS_VERSION_YOSEMITE);
+#endif
+}
+
 void MaybeReexec() {
   if (reexec_disabled) return;
 
   // Make sure the dynamic ASan runtime library is preloaded so that the
   // wrappers work. If it is not, set DYLD_INSERT_LIBRARIES and re-exec
   // ourselves.
   Dl_info info;
   CHECK(dladdr((void*)((uptr)__asan_init), &info));
   char *dyld_insert_libraries =
       const_cast<char*>(GetEnv(kDyldInsertLibraries));
   uptr old_env_len = dyld_insert_libraries ?
       internal_strlen(dyld_insert_libraries) : 0;
   uptr fname_len = internal_strlen(info.dli_fname);
   const char *dylib_name = StripModuleName(info.dli_fname);
   uptr dylib_name_len = internal_strlen(dylib_name);
-  if (!dyld_insert_libraries ||
-      !REAL(strstr)(dyld_insert_libraries, dylib_name)) {
+
+  bool lib_is_in_env =
+      dyld_insert_libraries && REAL(strstr)(dyld_insert_libraries, dylib_name);
+  if (DyldNeedsEnvVariable() && !lib_is_in_env) {
     // DYLD_INSERT_LIBRARIES is not set or does not contain the runtime
     // library.
     char program_name[1024];
     uint32_t buf_size = sizeof(program_name);
     _NSGetExecutablePath(program_name, &buf_size);
     char *new_env = const_cast<char*>(info.dli_fname);
     if (dyld_insert_libraries) {
       // Append the runtime dylib name to the existing value of
if (DyldNeedsEnvVariable() && !lib_is_in_env) {
     Report("ERROR: The process is launched without DYLD_INSERT_LIBRARIES, "
            "which is required for ASan to work. ASan tried to set the "
            "environment variable and re-execute itself, but execv() failed, "
            "possibly because of sandbox restrictions. Make sure to launch the "
            "executable with:\n%s=%s\n", kDyldInsertLibraries, new_env);
     CHECK("execv failed" && 0);
   }
 
+  if (!lib_is_in_env)
+    return;
+
   // DYLD_INSERT_LIBRARIES is set and contains the runtime library. Let's remove
   // the dylib from the environment variable, because interceptors are installed
   // and we don't want our children to inherit the variable.
 
   uptr env_name_len = internal_strlen(kDyldInsertLibraries);
   // Allocate memory to hold the previous env var name, its value, the '='
   // sign and the '\0' char.
   char *new_env = (char*)allocator_for_env.Allocate(

test/asan/TestCases/Darwin/dyld_insert_libraries_reexec.cc

 // When DYLD-inserting the ASan dylib from a different location than the
 // original, make sure we don't try to reexec.
 
 // RUN: mkdir -p %T/dyld_insert_libraries_reexec
 // RUN: cp `%clang_asan %s -fsanitize=address -### 2>&1 \
 // RUN:   | grep "libclang_rt.asan_osx_dynamic.dylib" \
 // RUN:   | sed -e 's/.*"\(.*libclang_rt.asan_osx_dynamic.dylib\)".*/\1/'` \
 // RUN:   %T/dyld_insert_libraries_reexec/libclang_rt.asan_osx_dynamic.dylib
 // RUN: %clangxx_asan %s -o %T/dyld_insert_libraries_reexec/a.out
+
 // RUN: env DYLD_INSERT_LIBRARIES=@executable_path/libclang_rt.asan_osx_dynamic.dylib \
 // RUN:   ASAN_OPTIONS=$ASAN_OPTIONS:verbosity=1 %run %T/dyld_insert_libraries_reexec/a.out 2>&1 \
 // RUN:   | FileCheck %s
-// RUN: env ASAN_OPTIONS=$ASAN_OPTIONS:verbosity=1 %run %T/dyld_insert_libraries_reexec/a.out 2>&1 \
-// RUN:   | FileCheck --check-prefix=CHECK-NOINSERT %s
+
+// RUN: IS_OSX_10_11_OR_HIGHER=$([ `sw_vers -productVersion | cut -d'.' -f2` -lt 11 ]; echo $?)
+
+// On OS X 10.10 and lower, if the dylib is not DYLD-inserted, ASan will re-exec.
+// RUN: if [ $IS_OSX_10_11_OR_HIGHER == 0 ]; then \
+// RUN:   env ASAN_OPTIONS=$ASAN_OPTIONS:verbosity=1 %run %T/dyld_insert_libraries_reexec/a.out 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NOINSERT %s; \
+// RUN:   fi
+
+// On OS X 10.11 and higher, we don't need to DYLD-insert anymore, and the interceptors
+// still installed correctly. Let's just check that things work and we don't try to re-exec.
+// RUN: if [ $IS_OSX_10_11_OR_HIGHER == 1 ]; then \
+// RUN:   env ASAN_OPTIONS=$ASAN_OPTIONS:verbosity=1 %run %T/dyld_insert_libraries_reexec/a.out 2>&1 \
+// RUN:   | FileCheck %s; \
+// RUN:   fi
 
 #include <stdio.h>
 
 int main() {
   printf("Passed\n");
   return 0;
 }