Improve and fix the stack-protector tests.

Bug: http://b/26888853
Change-Id: I505dbf7d5934f7247fb639f55dd6a9341df3947b

libc/bionic/__libc_init_main_thread.cpp

@@ -74,6 +74,10 @@ void __libc_init_main_thread(KernelArgumentBlock& args) {
   main_thread.attr.stack_size = 0; // User code should never see this; we'll compute it when asked.
   // TODO: the main thread's sched_policy and sched_priority need to be queried.
 
+  // The TLS stack guard is set from the global, so ensure that we've initialized the global
+  // before we initialize the TLS.
+  __libc_init_global_stack_chk_guard(args);
+
   __init_thread(&main_thread);
   __init_tls(&main_thread);
 

libc/bionic/libc_init_common.cpp

@@ -64,10 +64,17 @@ char** environ;
 // Declared in "private/bionic_ssp.h".
 uintptr_t __stack_chk_guard = 0;
 
+void __libc_init_global_stack_chk_guard(KernelArgumentBlock& args) {
+  // AT_RANDOM is a pointer to 16 bytes of randomness on the stack.
+  // Take the first 4/8 for the -fstack-protector implementation.
+  __stack_chk_guard = *reinterpret_cast<uintptr_t*>(args.getauxval(AT_RANDOM));
+}
+
 void __libc_init_globals(KernelArgumentBlock& args) {
   // Initialize libc globals that are needed in both the linker and in libc.
   // In dynamic binaries, this is run at least twice for different copies of the
   // globals, once for the linker's copy and once for the one in libc.so.
+  __libc_init_global_stack_chk_guard(args);
   __libc_auxv = args.auxv;
   __libc_globals.initialize();
   __libc_globals.mutate([&args](libc_globals* globals) {
@@ -83,9 +90,6 @@ void __libc_init_common(KernelArgumentBlock& args) {
   __progname = args.argv[0] ? args.argv[0] : "<unknown>";
   __abort_message_ptr = args.abort_message_ptr;
 
-  // AT_RANDOM is a pointer to 16 bytes of randomness on the stack.
-  __stack_chk_guard = *reinterpret_cast<uintptr_t*>(getauxval(AT_RANDOM));
-
   // Get the main thread from TLS and add it to the thread list.
   pthread_internal_t* main_thread = __get_thread();
   __pthread_internal_add(main_thread);

libc/private/bionic_globals.h

@@ -25,10 +25,12 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
+
 #ifndef _PRIVATE_BIONIC_GLOBALS_H
 #define _PRIVATE_BIONIC_GLOBALS_H
 
 #include <sys/cdefs.h>
+
 #include "private/bionic_malloc_dispatch.h"
 #include "private/bionic_vdso.h"
 #include "private/WriteProtected.h"
@@ -42,9 +44,9 @@ struct libc_globals {
 __LIBC_HIDDEN__ extern WriteProtected<libc_globals> __libc_globals;
 
 class KernelArgumentBlock;
-__LIBC_HIDDEN__ void __libc_init_vdso(libc_globals* globals,
-                                      KernelArgumentBlock& args);
-__LIBC_HIDDEN__ void __libc_init_setjmp_cookie(libc_globals* globals,
-                                               KernelArgumentBlock& args);
+__LIBC_HIDDEN__ void __libc_init_global_stack_chk_guard(KernelArgumentBlock& args);
 __LIBC_HIDDEN__ void __libc_init_malloc(libc_globals* globals);
+__LIBC_HIDDEN__ void __libc_init_setjmp_cookie(libc_globals* globals, KernelArgumentBlock& args);
+__LIBC_HIDDEN__ void __libc_init_vdso(libc_globals* globals, KernelArgumentBlock& args);
+
 #endif

libc/private/bionic_tls.h

@@ -30,7 +30,7 @@
 #define __BIONIC_PRIVATE_BIONIC_TLS_H_
 
 #include <sys/cdefs.h>
-#include <sys/limits.h>
+
 #include "bionic_macros.h"
 #include "__get_tls.h"
 
@@ -117,7 +117,7 @@ __END_DECLS
 
 #if defined(__cplusplus)
 class KernelArgumentBlock;
-extern __LIBC_HIDDEN__ void __libc_init_main_thread(KernelArgumentBlock&);
+extern void __libc_init_main_thread(KernelArgumentBlock&);
 #endif
 
 #endif /* __BIONIC_PRIVATE_BIONIC_TLS_H_ */

tests/Android.mk

@@ -78,6 +78,7 @@ libBionicStandardTests_src_files := \
     setjmp_test.cpp \
     signal_test.cpp \
     stack_protector_test.cpp \
+    stack_protector_test_helper.cpp \
     stack_unwinding_test.cpp \
     stdatomic_test.cpp \
     stdint_test.cpp \

tests/stack_protector_test.cpp

@@ -27,108 +27,83 @@
 #include <unistd.h>
 #include <set>
 
-extern "C" pid_t gettid();
+#include "private/bionic_tls.h"
 
-// For x86, bionic and glibc have per-thread stack guard values (all identical).
-#if defined(__i386__)
-static uint32_t GetGuardFromTls() {
-  uint32_t guard;
-  asm ("mov %%gs:0x14, %0": "=d" (guard));
-  return guard;
-}
+extern "C" pid_t gettid(); // glibc defines this but doesn't declare it anywhere.
+
+#if defined(__BIONIC__)
+extern uintptr_t __stack_chk_guard;
+#endif
 
 struct stack_protector_checker {
   std::set<pid_t> tids;
-  std::set<uint32_t> guards;
+  std::set<void*> guards;
 
   void Check() {
     pid_t tid = gettid();
-    uint32_t guard = GetGuardFromTls();
+    void* guard = __get_tls()[TLS_SLOT_STACK_GUARD];
 
-    printf("[thread %d] %%gs:0x14 = 0x%08x\n", tid, guard);
+    printf("[thread %d] TLS stack guard = %p\n", tid, guard);
 
     // Duplicate tid. gettid(2) bug? Seeing this would be very upsetting.
     ASSERT_TRUE(tids.find(tid) == tids.end());
 
-    // Uninitialized guard. Our bug. Note this is potentially flaky; we _could_ get
-    // four random zero bytes, but it should be vanishingly unlikely.
-    ASSERT_NE(guard, 0U);
+    // Uninitialized guard. Our bug. Note this is potentially flaky; we _could_
+    // get four random zero bytes, but it should be vanishingly unlikely.
+    ASSERT_NE(guard, nullptr);
+
+#if defined(__BIONIC__)
+    // bionic always has the global too.
+    ASSERT_EQ(__stack_chk_guard, reinterpret_cast<uintptr_t>(guard));
+#endif
 
     tids.insert(tid);
     guards.insert(guard);
   }
 };
 
-static void* ThreadGuardHelper(void* arg) {
-  stack_protector_checker* checker = reinterpret_cast<stack_protector_checker*>(arg);
-  checker->Check();
-  return NULL;
-}
-#endif // __i386__
-
 TEST(stack_protector, same_guard_per_thread) {
-#if defined(__i386__)
+  // Everyone has the TLS slot set, even if their stack protector
+  // implementation doesn't yet use it.
   stack_protector_checker checker;
-  size_t thread_count = 10;
-  for (size_t i = 0; i < thread_count; ++i) {
+
+  // Check the main thread.
+  ASSERT_EQ(getpid(), gettid()); // We are the main thread, right?
+  checker.Check();
+
+  size_t thread_count = 9;
+  for (size_t i = 1; i < thread_count; ++i) {
     pthread_t t;
-    ASSERT_EQ(0, pthread_create(&t, NULL, ThreadGuardHelper, &checker));
+    ASSERT_EQ(0, pthread_create(&t, NULL, [](void* arg) -> void* {
+      stack_protector_checker* checker = reinterpret_cast<stack_protector_checker*>(arg);
+      checker->Check();
+      return nullptr;
+    }, &checker));
     void* result;
     ASSERT_EQ(0, pthread_join(t, &result));
     ASSERT_EQ(NULL, result);
   }
   ASSERT_EQ(thread_count, checker.tids.size());
 
-  // bionic and glibc use the same guard for every thread.
+  // Both bionic and glibc use the same guard for every thread.
   ASSERT_EQ(1U, checker.guards.size());
-#else // __i386__
-  GTEST_LOG_(INFO) << "This test does nothing.\n";
-#endif // __i386__
 }
 
-// For ARM and MIPS, glibc has a global stack check guard value.
-#if defined(__BIONIC__) || defined(__arm__) || defined(__mips__)
-#define TEST_STACK_CHK_GUARD
-
-// Bionic has the global for x86 too, to support binaries that can run on
-// Android releases that didn't implement the TLS guard value.
-extern "C" uintptr_t __stack_chk_guard;
-
-/*
- * When this function returns, the stack canary will be inconsistent
- * with the previous value, which will generate a call to __stack_chk_fail(),
- * eventually resulting in a SIGABRT.
- *
- * This must be marked with "__attribute__ ((noinline))", to ensure the
- * compiler generates the proper stack guards around this function.
- */
-static char* dummy_buf;
-
-__attribute__ ((noinline))
-static void do_modify_stack_chk_guard() {
-  char buf[128];
-  // Store local array's address to global variable to force compiler to generate stack guards.
-  dummy_buf = buf;
-  __stack_chk_guard = 0x12345678;
-}
-
-#endif
-
 TEST(stack_protector, global_guard) {
-#if defined(TEST_STACK_CHK_GUARD)
+#if defined(__BIONIC__)
+  // Bionic always has a global, even if it's using TLS.
   ASSERT_NE(0, gettid());
   ASSERT_NE(0U, __stack_chk_guard);
-#else // TEST_STACK_CHK_GUARD
-  GTEST_LOG_(INFO) << "This test does nothing.\n";
-#endif // TEST_STACK_CHK_GUARD
+#else
+  GTEST_LOG_(INFO) << "glibc doesn't have a global __stack_chk_guard.\n";
+#endif
 }
 
 class stack_protector_DeathTest : public BionicDeathTest {};
 
 TEST_F(stack_protector_DeathTest, modify_stack_protector) {
-#if defined(TEST_STACK_CHK_GUARD)
-  ASSERT_EXIT(do_modify_stack_chk_guard(), testing::KilledBySignal(SIGABRT), "");
-#else // TEST_STACK_CHK_GUARD
-  GTEST_LOG_(INFO) << "This test does nothing.\n";
-#endif // TEST_STACK_CHK_GUARD
+  // In another file to prevent inlining, which removes stack protection.
+  extern void modify_stack_protector_test();
+  ASSERT_EXIT(modify_stack_protector_test(),
+              testing::KilledBySignal(SIGABRT), "stack corruption detected");
 }

tests/stack_protector_test_helper.cpp

@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * 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.
+ */
+
+// Deliberately overwrite the stack canary.
+__attribute__((noinline)) void modify_stack_protector_test() {
+  char buf[128];
+  // We can't use memset here because it's fortified, and we want to test
+  // the line of defense *after* that.
+  char* p = buf;
+  while ((p - buf) < static_cast<int>(sizeof(buf) + sizeof(void*))) *p++ = '\0';
+}