[compiler-rt] Abort after failed exec() and get rid of the allow_reexec ASan flag

[kubamracek]

Summary

As mentioned in https://code.google.com/p/address-sanitizer/issues/detail?id=365, when the re-exec that adds the required DYLD_INSERT_LIBRARIES variable fails, ASan currently continues to run, but things are broken (some memory can be overwritten, interceptors don't work, ...). This patch aborts if the execv() fails and prints an error message that DYLD_INSERT_LIBRARIES is required. It also removes the "alllow_reexec" flag, since using it causes the same issues.

[glider]

LGTM. Thank you.

[kubamracek]

Landed in r224712!

lib/asan/asan_flags.h

struct Flags {
   bool allow_user_poisoning;
   int  sleep_before_dying;
   bool check_malloc_usable_size;
   bool unmap_shadow_on_exit;
   bool abort_on_error;
   bool print_stats;
   bool print_legend;
   bool atexit;
-  bool allow_reexec;
   bool print_full_thread_history;
   bool poison_heap;
   bool poison_partial;
   bool poison_array_cookie;
   bool alloc_dealloc_mismatch;
   bool new_delete_type_mismatch;
   bool strict_memcmp;
   bool strict_init_order;

lib/asan/asan_flags.cc

ParseFlag(str, &f->print_stats, "print_stats",
       "Print various statistics after printing an error message or if "
       "atexit=1.");
   ParseFlag(str, &f->print_legend, "print_legend",
       "Print the legend for the shadow bytes.");
   ParseFlag(str, &f->atexit, "atexit",
       "If set, prints ASan exit stats even after program terminates "
       "successfully.");
 
-  ParseFlag(str, &f->allow_reexec, "allow_reexec",
-      "Allow the tool to re-exec the program. This may interfere badly with "
-      "the debugger.");
-
   ParseFlag(str, &f->print_full_thread_history,
       "print_full_thread_history",
       "If set, prints thread creation stacks for the threads involved in the "
       "report and their ancestors up to the main thread.");
 
   ParseFlag(str, &f->poison_heap, "poison_heap",
       "Poison (or not) the heap memory on [de]allocation. Zero value is useful "
       "for benchmarking the allocator or instrumentator.");
void InitializeFlags(Flags *f) {
   f->allow_user_poisoning = true;
   f->sleep_before_dying = 0;
   f->check_malloc_usable_size = true;
   f->unmap_shadow_on_exit = false;
   f->abort_on_error = false;
   f->print_stats = false;
   f->print_legend = true;
   f->atexit = false;
-  f->allow_reexec = true;
   f->print_full_thread_history = true;
   f->poison_heap = true;
   f->poison_array_cookie = true;
   f->poison_partial = true;
   // Turn off alloc/dealloc mismatch checker on Mac and Windows for now.
   // https://code.google.com/p/address-sanitizer/issues/detail?id=131
   // https://code.google.com/p/address-sanitizer/issues/detail?id=309
   // TODO(glider,timurrrr): Fix known issues and enable this back.

lib/asan/asan_mac.cc

if (len > name_len) {
         }
       }
     }
     environ++;
   }
 }
 
 void MaybeReexec() {
-  if (!flags()->allow_reexec) 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 ?
if (dyld_insert_libraries) {
       setenv(kDyldInsertLibraries, new_env, /*overwrite*/1);
     } else {
       // Set DYLD_INSERT_LIBRARIES equal to the runtime dylib name.
       setenv(kDyldInsertLibraries, info.dli_fname, /*overwrite*/0);
     }
     VReport(1, "exec()-ing the program with\n");
     VReport(1, "%s=%s\n", kDyldInsertLibraries, new_env);
     VReport(1, "to enable ASan wrappers.\n");
-    VReport(1, "Set ASAN_OPTIONS=allow_reexec=0 to disable this.\n");
     execv(program_name, *_NSGetArgv());
+
+    // We get here only if execv() failed.
+    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);
   } else {
     // DYLD_INSERT_LIBRARIES is set and contains the runtime library.
     if (old_env_len == fname_len) {
       // It's just the runtime library name - fine to unset the variable.
       LeakyResetEnv(kDyldInsertLibraries, NULL);
     } else {
       uptr env_name_len = internal_strlen(kDyldInsertLibraries);
       // Allocate memory to hold the previous env var name, its value, the '='

lib/asan/tests/asan_noinst_test.cc

 #include <vector>
 #include <limits>
 
 // ATTENTION!
 // Please don't call intercepted functions (including malloc() and friends)
 // in this test. The static runtime library is linked explicitly (without
 // -fsanitize=address), thus the interceptors do not work correctly on OS X.
 
-#if !defined(_WIN32)
-extern "C" {
-// Set specific ASan options for uninstrumented unittest.
-const char* __asan_default_options() {
-  return "allow_reexec=0";
-}
-}  // extern "C"
-#endif
-
 // Make sure __asan_init is called before any test case is run.
 struct AsanInitCaller {
   AsanInitCaller() { __asan_init(); }
 };
 static AsanInitCaller asan_init_caller;
 
 TEST(AddressSanitizer, InternalSimpleDeathTest) {
   EXPECT_DEATH(exit(1), "");