Index: lib/asan/asan_rtl.cc
===================================================================
--- lib/asan/asan_rtl.cc
+++ lib/asan/asan_rtl.cc
@@ -298,7 +298,7 @@
 }
 
 static void ProtectGap(uptr a, uptr size) {
-  void *res = Mprotect(a, size);
+  void *res = MmapNoAccess(a, size);
   if (a == (uptr)res)
     return;
   Report("ERROR: Failed to protect the shadow gap. "
Index: lib/dfsan/dfsan.cc
===================================================================
--- lib/dfsan/dfsan.cc
+++ lib/dfsan/dfsan.cc
@@ -368,7 +368,7 @@
   // case by disabling memory protection when ASLR is disabled.
   uptr init_addr = (uptr)&dfsan_init;
   if (!(init_addr >= kUnusedAddr && init_addr < kAppAddr))
-    Mprotect(kUnusedAddr, kAppAddr - kUnusedAddr);
+    MmapNoAccess(kUnusedAddr, kAppAddr - kUnusedAddr);
 
   InitializeFlags();
   InitializeInterceptors();
Index: lib/msan/msan_linux.cc
===================================================================
--- lib/msan/msan_linux.cc
+++ lib/msan/msan_linux.cc
@@ -56,7 +56,7 @@
 static bool ProtectMemoryRange(uptr beg, uptr size) {
   if (size > 0) {
     uptr end = beg + size - 1;
-    if (!Mprotect(beg, size)) {
+    if (!MmapNoAccess(beg, size)) {
       Printf("FATAL: Cannot protect memory range %p - %p.\n", beg, end);
       return false;
     }
Index: lib/sanitizer_common/sanitizer_allocator.h
===================================================================
--- lib/sanitizer_common/sanitizer_allocator.h
+++ lib/sanitizer_common/sanitizer_allocator.h
@@ -323,7 +323,7 @@
 
   void Init() {
     CHECK_EQ(kSpaceBeg,
-             reinterpret_cast<uptr>(Mprotect(kSpaceBeg, kSpaceSize)));
+             reinterpret_cast<uptr>(MmapNoAccess(kSpaceBeg, kSpaceSize)));
     MapWithCallback(kSpaceEnd, AdditionalSize());
   }
 
Index: lib/sanitizer_common/sanitizer_common.h
===================================================================
--- lib/sanitizer_common/sanitizer_common.h
+++ lib/sanitizer_common/sanitizer_common.h
@@ -72,9 +72,13 @@
 void *MmapFixedNoReserve(uptr fixed_addr, uptr size);
 void *MmapNoReserveOrDie(uptr size, const char *mem_type);
 void *MmapFixedOrDie(uptr fixed_addr, uptr size);
-void *Mprotect(uptr fixed_addr, uptr size);
+void *MmapNoAccess(uptr fixed_addr, uptr size);
 // Map aligned chunk of address space; size and alignment are powers of two.
 void *MmapAlignedOrDie(uptr size, uptr alignment, const char *mem_type);
+// Disallow access to a memory range.  Use MmapNoAccess to allocate an
+// unaccessible memory.
+bool MprotectNoAccess(uptr addr, uptr size);
+
 // Used to check if we can map shadow memory to a fixed location.
 bool MemoryRangeIsAvailable(uptr range_start, uptr range_end);
 void FlushUnneededShadowMemory(uptr addr, uptr size);
Index: lib/sanitizer_common/sanitizer_coverage_libcdep.cc
===================================================================
--- lib/sanitizer_common/sanitizer_coverage_libcdep.cc
+++ lib/sanitizer_common/sanitizer_coverage_libcdep.cc
@@ -211,8 +211,9 @@
   tr_event_array = reinterpret_cast<u32 *>(MmapNoReserveOrDie(
       sizeof(tr_event_array[0]) * kTrEventArrayMaxSize + GetMmapGranularity(),
       "CovInit::tr_event_array"));
-  Mprotect(reinterpret_cast<uptr>(&tr_event_array[kTrEventArrayMaxSize]),
-           GetMmapGranularity());
+  MprotectNoAccess(
+      reinterpret_cast<uptr>(&tr_event_array[kTrEventArrayMaxSize]),
+      GetMmapGranularity());
   tr_event_array_size = kTrEventArrayMaxSize;
   tr_event_pointer = tr_event_array;
 
Index: lib/sanitizer_common/sanitizer_linux.cc
===================================================================
--- lib/sanitizer_common/sanitizer_linux.cc
+++ lib/sanitizer_common/sanitizer_linux.cc
@@ -127,6 +127,10 @@
   return internal_syscall(SYSCALL(munmap), (uptr)addr, length);
 }
 
+int internal_mprotect(void *addr, uptr length, int prot) {
+  return internal_syscall(SYSCALL(mprotect), addr, length, prot);
+}
+
 uptr internal_close(fd_t fd) {
   return internal_syscall(SYSCALL(close), fd);
 }
Index: lib/sanitizer_common/sanitizer_mac.cc
===================================================================
--- lib/sanitizer_common/sanitizer_mac.cc
+++ lib/sanitizer_common/sanitizer_mac.cc
@@ -59,6 +59,10 @@
   return munmap(addr, length);
 }
 
+int internal_mprotect(void *addr, uptr length, int prot) {
+  return mprotect(addr, length, prot);
+}
+
 uptr internal_close(fd_t fd) {
   return close(fd);
 }
Index: lib/sanitizer_common/sanitizer_posix.h
===================================================================
--- lib/sanitizer_common/sanitizer_posix.h
+++ lib/sanitizer_common/sanitizer_posix.h
@@ -37,6 +37,7 @@
 uptr internal_mmap(void *addr, uptr length, int prot, int flags,
                    int fd, u64 offset);
 uptr internal_munmap(void *addr, uptr length);
+int internal_mprotect(void *addr, uptr length, int prot);
 
 // OS
 uptr internal_filesize(fd_t fd);  // -1 on error.
Index: lib/sanitizer_common/sanitizer_posix.cc
===================================================================
--- lib/sanitizer_common/sanitizer_posix.cc
+++ lib/sanitizer_common/sanitizer_posix.cc
@@ -199,13 +199,17 @@
   return (void *)p;
 }
 
-void *Mprotect(uptr fixed_addr, uptr size) {
+void *MmapNoAccess(uptr fixed_addr, uptr size) {
   return (void *)internal_mmap((void*)fixed_addr, size,
                                PROT_NONE,
                                MAP_PRIVATE | MAP_ANON | MAP_FIXED |
                                MAP_NORESERVE, -1, 0);
 }
 
+bool MprotectNoAccess(uptr addr, uptr size) {
+  return 0 == internal_mprotect((void*)addr, size, PROT_NONE);
+}
+
 fd_t OpenFile(const char *filename, FileAccessMode mode, error_t *errno_p) {
   int flags;
   switch (mode) {
Index: lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc
===================================================================
--- lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc
+++ lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cc
@@ -310,7 +310,7 @@
     // in the future.
     guard_start_ = (uptr)MmapOrDie(stack_size_ + guard_size_,
                                    "ScopedStackWithGuard");
-    CHECK_EQ(guard_start_, (uptr)Mprotect((uptr)guard_start_, guard_size_));
+    CHECK(MprotectNoAccess((uptr)guard_start_, guard_size_));
   }
   ~ScopedStackSpaceWithGuard() {
     UnmapOrDie((void *)guard_start_, stack_size_ + guard_size_);
Index: lib/sanitizer_common/sanitizer_win.cc
===================================================================
--- lib/sanitizer_common/sanitizer_win.cc
+++ lib/sanitizer_common/sanitizer_win.cc
@@ -125,7 +125,7 @@
   return MmapOrDie(size, mem_type);
 }
 
-void *Mprotect(uptr fixed_addr, uptr size) {
+void *MmapNoAccess(uptr fixed_addr, uptr size) {
   void *res = VirtualAlloc((LPVOID)fixed_addr, size,
                            MEM_RESERVE | MEM_COMMIT, PAGE_NOACCESS);
   if (res == 0)
@@ -135,6 +135,12 @@
   return res;
 }
 
+bool MprotectNoAccess(uptr addr, uptr size) {
+  DWORD old_protection;
+  return VirtualProtect((LPVOID)addr, size, PAGE_NOACCESS, &old_protection);
+}
+
+
 void FlushUnneededShadowMemory(uptr addr, uptr size) {
   // This is almost useless on 32-bits.
   // FIXME: add madvise-analog when we move to 64-bits.
Index: lib/sanitizer_common/tests/sanitizer_stacktrace_test.cc
===================================================================
--- lib/sanitizer_common/tests/sanitizer_stacktrace_test.cc
+++ lib/sanitizer_common/tests/sanitizer_stacktrace_test.cc
@@ -45,7 +45,7 @@
 void FastUnwindTest::SetUp() {
   size_t ps = GetPageSize();
   mapping = MmapOrDie(2 * ps, "FastUnwindTest");
-  Mprotect((uptr)mapping, ps);
+  MprotectNoAccess((uptr)mapping, ps);
 
   // Unwinder may peek 1 word down from the starting FP.
   fake_stack = (uhwptr *)((uptr)mapping + ps + sizeof(uhwptr));
Index: lib/tsan/rtl/tsan_platform_linux.cc
===================================================================
--- lib/tsan/rtl/tsan_platform_linux.cc
+++ lib/tsan/rtl/tsan_platform_linux.cc
@@ -136,7 +136,7 @@
   CHECK_LE(beg, end);
   if (beg == end)
     return;
-  if (beg != (uptr)Mprotect(beg, end - beg)) {
+  if (beg != (uptr)MmapNoAccess(beg, end - beg)) {
     Printf("FATAL: ThreadSanitizer can not protect [%zx,%zx]\n", beg, end);
     Printf("FATAL: Make sure you are not using unlimited stack\n");
     Die();