Add some MTE-related helpers.

mte_supported() lets code efficiently detect the presence of MTE, and
ScopedDisableMTE lets code disable MTE RAII-style in a particular region
of code.

Bug: 135772972
Change-Id: I628a054b50d79f67f39f35d44232b7a2ae166afb

libc/Android.bp

@@ -1797,7 +1797,7 @@ cc_library_headers {
     name: "bionic_libc_platform_headers",
     visibility: [
         "//art:__subpackages__",
-        "//bionic/libc:__subpackages__",
+        "//bionic:__subpackages__",
         "//frameworks:__subpackages__",
         "//external/perfetto:__subpackages__",
         "//external/scudo:__subpackages__",

libc/bionic/getauxval.cpp

@@ -31,6 +31,7 @@
 #include <sys/auxv.h>
 #include <private/bionic_auxv.h>
 #include <private/bionic_globals.h>
+#include <private/bionic_ifuncs.h>
 #include <elf.h>
 #include <errno.h>
 

libc/platform/bionic/mte.h

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <sys/auxv.h>
+#include <bionic/mte_kernel.h>
+
+#ifdef __aarch64__
+inline bool mte_supported() {
+#ifdef ANDROID_EXPERIMENTAL_MTE
+  static bool supported = getauxval(AT_HWCAP2) & HWCAP2_MTE;
+#else
+  static bool supported = false;
+#endif
+  return supported;
+}
+#endif
+
+struct ScopedDisableMTE {
+  ScopedDisableMTE() {
+#ifdef __aarch64__
+    if (mte_supported()) {
+      __asm__ __volatile__(".arch_extension mte; msr tco, #1");
+    }
+#endif
+  }
+
+  ~ScopedDisableMTE() {
+#ifdef __aarch64__
+    if (mte_supported()) {
+      __asm__ __volatile__(".arch_extension mte; msr tco, #0");
+    }
+#endif
+  }
+};

tests/Android.bp

@@ -38,6 +38,7 @@ cc_defaults {
         // For glibc.
         "-D__STDC_LIMIT_MACROS",
     ],
+    header_libs: ["bionic_libc_platform_headers"],
     // Make the bionic tests implicitly test bionic's shadow call stack support.
     arch: {
         arm64: {
@@ -49,6 +50,12 @@ cc_defaults {
         address: false,
     },
     bootstrap: true,
+
+    product_variables: {
+        experimental_mte: {
+            cflags: ["-DANDROID_EXPERIMENTAL_MTE"],
+        },
+    },
 }
 
 // -----------------------------------------------------------------------------
@@ -117,6 +124,7 @@ cc_test_library {
         "math_force_long_double_test.cpp",
         "membarrier_test.cpp",
         "mntent_test.cpp",
+        "mte_test.cpp",
         "netdb_test.cpp",
         "net_if_test.cpp",
         "netinet_ether_test.cpp",

tests/mte_test.cpp

@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2020 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.
+ */
+
+#include <gtest/gtest.h>
+
+#include <bionic/mte.h>
+
+__attribute__((no_sanitize("hwaddress")))
+static void test_tag_mismatch() {
+  ScopedDisableMTE x;
+#if defined(__aarch64__)
+  std::unique_ptr<int[]> p = std::make_unique<int[]>(4);
+  p[0] = 1;
+  int* mistagged_p = reinterpret_cast<int*>(reinterpret_cast<uintptr_t>(p.get()) + (1ULL << 56));
+  volatile int load = *mistagged_p;
+  (void)load;
+#endif
+}
+
+TEST(mte_test, ScopedDisableMTE) {
+  test_tag_mismatch();
+}