os_utils.cpp

/*
* OS and machine specific utility functions
* (C) 2015,2016,2017,2018 Jack Lloyd
* (C) 2016 Daniel Neus
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/internal/os_utils.h>
#include <botan/cpuid.h>
#include <botan/exceptn.h>
#include <botan/mem_ops.h>

#include <algorithm>
#include <chrono>
#include <cstdlib>

#if defined(BOTAN_TARGET_OS_HAS_THREADS)
  #include <thread>
#endif

#if defined(BOTAN_TARGET_OS_HAS_EXPLICIT_BZERO)
  #include <string.h>
#endif

#if defined(BOTAN_TARGET_OS_HAS_POSIX1)
  #include <sys/types.h>
  #include <sys/resource.h>
  #include <sys/mman.h>
  #include <signal.h>
  #include <stdlib.h>
  #include <setjmp.h>
  #include <unistd.h>
  #include <errno.h>
  #include <termios.h>
  #undef B0
#endif

#if defined(BOTAN_TARGET_OS_IS_EMSCRIPTEN)
  #include <emscripten/emscripten.h>
#endif

#if defined(BOTAN_TARGET_OS_HAS_GETAUXVAL) || defined(BOTAN_TARGET_OS_IS_ANDROID) || \
  defined(BOTAN_TARGET_OS_HAS_ELF_AUX_INFO)
  #include <sys/auxv.h>
#endif

#if defined(BOTAN_TARGET_OS_HAS_WIN32)
  #define NOMINMAX 1
  #define _WINSOCKAPI_ // stop windows.h including winsock.h
  #include <windows.h>
#endif

#if defined(BOTAN_TARGET_OS_IS_ANDROID)
  #include <elf.h>
  extern "C" char **environ;
#endif

#if defined(BOTAN_TARGET_OS_IS_IOS) || defined(BOTAN_TARGET_OS_IS_MACOS)
  #include <mach/vm_statistics.h>
#endif

namespace Botan {

// Not defined in OS namespace for historical reasons
void secure_scrub_memory(void* ptr, size_t n)
   {
#if defined(BOTAN_TARGET_OS_HAS_RTLSECUREZEROMEMORY)
   ::RtlSecureZeroMemory(ptr, n);

#elif defined(BOTAN_TARGET_OS_HAS_EXPLICIT_BZERO)
   ::explicit_bzero(ptr, n);

#elif defined(BOTAN_TARGET_OS_HAS_EXPLICIT_MEMSET)
   (void)::explicit_memset(ptr, 0, n);

#elif defined(BOTAN_USE_VOLATILE_MEMSET_FOR_ZERO) && (BOTAN_USE_VOLATILE_MEMSET_FOR_ZERO == 1)
   /*
   Call memset through a static volatile pointer, which the compiler
   should not elide. This construct should be safe in conforming
   compilers, but who knows. I did confirm that on x86-64 GCC 6.1 and
   Clang 3.8 both create code that saves the memset address in the
   data segment and unconditionally loads and jumps to that address.
   */
   static void* (*const volatile memset_ptr)(void*, int, size_t) = std::memset;
   (memset_ptr)(ptr, 0, n);
#else

   volatile uint8_t* p = reinterpret_cast<volatile uint8_t*>(ptr);

   for(size_t i = 0; i != n; ++i)
      p[i] = 0;
#endif
   }

uint32_t OS::get_process_id()
   {
#if defined(BOTAN_TARGET_OS_HAS_POSIX1)
   return ::getpid();
#elif defined(BOTAN_TARGET_OS_HAS_WIN32)
   return ::GetCurrentProcessId();
#elif defined(BOTAN_TARGET_OS_IS_INCLUDEOS) || defined(BOTAN_TARGET_OS_IS_LLVM) || defined(BOTAN_TARGET_OS_IS_NONE)
   return 0; // truly no meaningful value
#else
   #error "Missing get_process_id"
#endif
   }

unsigned long OS::get_auxval(unsigned long id)
   {
#if defined(BOTAN_TARGET_OS_HAS_GETAUXVAL)
   return ::getauxval(id);
#elif defined(BOTAN_TARGET_OS_IS_ANDROID) && defined(BOTAN_TARGET_ARCH_IS_ARM32)

   if(id == 0)
      return 0;

   char **p = environ;

   while(*p++ != nullptr)
      ;

   Elf32_auxv_t *e = reinterpret_cast<Elf32_auxv_t*>(p);

   while(e != nullptr)
      {
      if(e->a_type == id)
         return e->a_un.a_val;
      e++;
      }

   return 0;
#elif defined(BOTAN_TARGET_OS_HAS_ELF_AUX_INFO)
   unsigned long auxinfo = 0;
   ::elf_aux_info(id, &auxinfo, sizeof(auxinfo));
   return auxinfo;
#else
   BOTAN_UNUSED(id);
   return 0;
#endif
   }

bool OS::running_in_privileged_state()
   {
#if defined(AT_SECURE)
   return OS::get_auxval(AT_SECURE) != 0;
#elif defined(BOTAN_TARGET_OS_HAS_POSIX1)
   return (::getuid() != ::geteuid()) || (::getgid() != ::getegid());
#else
   return false;
#endif
   }

uint64_t OS::get_cpu_cycle_counter()
   {
   uint64_t rtc = 0;

#if defined(BOTAN_TARGET_OS_HAS_WIN32)
   LARGE_INTEGER tv;
   ::QueryPerformanceCounter(&tv);
   rtc = tv.QuadPart;

#elif defined(BOTAN_USE_GCC_INLINE_ASM)

#if defined(BOTAN_TARGET_CPU_IS_X86_FAMILY)

   if(CPUID::has_rdtsc())
      {
      uint32_t rtc_low = 0, rtc_high = 0;
      asm volatile("rdtsc" : "=d" (rtc_high), "=a" (rtc_low));
      rtc = (static_cast<uint64_t>(rtc_high) << 32) | rtc_low;
      }

#elif defined(BOTAN_TARGET_ARCH_IS_PPC64)

   for(;;)
      {
      uint32_t rtc_low = 0, rtc_high = 0, rtc_high2 = 0;
      asm volatile("mftbu %0" : "=r" (rtc_high));
      asm volatile("mftb %0" : "=r" (rtc_low));
      asm volatile("mftbu %0" : "=r" (rtc_high2));

      if(rtc_high == rtc_high2)
         {
         rtc = (static_cast<uint64_t>(rtc_high) << 32) | rtc_low;
         break;
         }
      }

#elif defined(BOTAN_TARGET_ARCH_IS_ALPHA)
   asm volatile("rpcc %0" : "=r" (rtc));

   // OpenBSD does not trap access to the %tick register
#elif defined(BOTAN_TARGET_ARCH_IS_SPARC64) && !defined(BOTAN_TARGET_OS_IS_OPENBSD)
   asm volatile("rd %%tick, %0" : "=r" (rtc));

#elif defined(BOTAN_TARGET_ARCH_IS_IA64)
   asm volatile("mov %0=ar.itc" : "=r" (rtc));

#elif defined(BOTAN_TARGET_ARCH_IS_S390X)
   asm volatile("stck 0(%0)" : : "a" (&rtc) : "memory", "cc");

#elif defined(BOTAN_TARGET_ARCH_IS_HPPA)
   asm volatile("mfctl 16,%0" : "=r" (rtc)); // 64-bit only?

#else
   //#warning "OS::get_cpu_cycle_counter not implemented"
#endif

#endif

   return rtc;
   }

size_t OS::get_cpu_total()
   {
#if defined(BOTAN_TARGET_OS_HAS_POSIX1) && defined(_SC_NPROCESSORS_CONF)
   const long res = ::sysconf(_SC_NPROCESSORS_CONF);
   if(res > 0)
      return static_cast<size_t>(res);
#endif

#if defined(BOTAN_TARGET_OS_HAS_THREADS)
   return static_cast<size_t>(std::thread::hardware_concurrency());
#else
   return 1;
#endif
   }

size_t OS::get_cpu_available()
   {
#if defined(BOTAN_TARGET_OS_HAS_POSIX1) && defined(_SC_NPROCESSORS_ONLN)
   const long res = ::sysconf(_SC_NPROCESSORS_ONLN);
   if(res > 0)
      return static_cast<size_t>(res);
#endif

   return OS::get_cpu_total();
   }

uint64_t OS::get_high_resolution_clock()
   {
   if(uint64_t cpu_clock = OS::get_cpu_cycle_counter())
      return cpu_clock;

#if defined(BOTAN_TARGET_OS_IS_EMSCRIPTEN)
   return emscripten_get_now();
#endif

   /*
   If we got here either we either don't have an asm instruction
   above, or (for x86) RDTSC is not available at runtime. Try some
   clock_gettimes and return the first one that works, or otherwise
   fall back to std::chrono.
   */

#if defined(BOTAN_TARGET_OS_HAS_CLOCK_GETTIME)

   // The ordering here is somewhat arbitrary...
   const clockid_t clock_types[] = {
#if defined(CLOCK_MONOTONIC_HR)
      CLOCK_MONOTONIC_HR,
#endif
#if defined(CLOCK_MONOTONIC_RAW)
      CLOCK_MONOTONIC_RAW,
#endif
#if defined(CLOCK_MONOTONIC)
      CLOCK_MONOTONIC,
#endif
#if defined(CLOCK_PROCESS_CPUTIME_ID)
      CLOCK_PROCESS_CPUTIME_ID,
#endif
#if defined(CLOCK_THREAD_CPUTIME_ID)
      CLOCK_THREAD_CPUTIME_ID,
#endif
   };

   for(clockid_t clock : clock_types)
      {
      struct timespec ts;
      if(::clock_gettime(clock, &ts) == 0)
         {
         return (static_cast<uint64_t>(ts.tv_sec) * 1000000000) + static_cast<uint64_t>(ts.tv_nsec);
         }
      }
#endif

   // Plain C++11 fallback
   auto now = std::chrono::high_resolution_clock::now().time_since_epoch();
   return std::chrono::duration_cast<std::chrono::nanoseconds>(now).count();
   }

uint64_t OS::get_system_timestamp_ns()
   {
#if defined(BOTAN_TARGET_OS_HAS_CLOCK_GETTIME)
   struct timespec ts;
   if(::clock_gettime(CLOCK_REALTIME, &ts) == 0)
      {
      return (static_cast<uint64_t>(ts.tv_sec) * 1000000000) + static_cast<uint64_t>(ts.tv_nsec);
      }
#endif

   auto now = std::chrono::system_clock::now().time_since_epoch();
   return std::chrono::duration_cast<std::chrono::nanoseconds>(now).count();
   }

size_t OS::system_page_size()
   {
   const size_t default_page_size = 4096;

#if defined(BOTAN_TARGET_OS_HAS_POSIX1)
   long p = ::sysconf(_SC_PAGESIZE);
   if(p > 1)
      return static_cast<size_t>(p);
   else
      return default_page_size;
#elif defined(BOTAN_TARGET_OS_HAS_VIRTUAL_LOCK)
   BOTAN_UNUSED(default_page_size);
   SYSTEM_INFO sys_info;
   ::GetSystemInfo(&sys_info);
   return sys_info.dwPageSize;
#else
   return default_page_size;
#endif
   }

size_t OS::get_memory_locking_limit()
   {
#if defined(BOTAN_TARGET_OS_HAS_POSIX1) && defined(BOTAN_TARGET_OS_HAS_POSIX_MLOCK) && defined(RLIMIT_MEMLOCK)
   /*
   * If RLIMIT_MEMLOCK is not defined, likely the OS does not support
   * unprivileged mlock calls.
   *
   * Linux defaults to only 64 KiB of mlockable memory per process
   * (too small) but BSDs offer a small fraction of total RAM (more
   * than we need). Bound the total mlock size to 512 KiB which is
   * enough to run the entire test suite without spilling to non-mlock
   * memory (and thus presumably also enough for many useful
   * programs), but small enough that we should not cause problems
   * even if many processes are mlocking on the same machine.
   */
   const size_t user_req = read_env_variable_sz("BOTAN_MLOCK_POOL_SIZE", BOTAN_MLOCK_ALLOCATOR_MAX_LOCKED_KB);

   const size_t mlock_requested = std::min<size_t>(user_req, BOTAN_MLOCK_ALLOCATOR_MAX_LOCKED_KB);

   if(mlock_requested > 0)
      {
      struct ::rlimit limits;

      ::getrlimit(RLIMIT_MEMLOCK, &limits);

      if(limits.rlim_cur < limits.rlim_max)
         {
         limits.rlim_cur = limits.rlim_max;
         ::setrlimit(RLIMIT_MEMLOCK, &limits);
         ::getrlimit(RLIMIT_MEMLOCK, &limits);
         }

      return std::min<size_t>(limits.rlim_cur, mlock_requested * 1024);
      }

#elif defined(BOTAN_TARGET_OS_HAS_VIRTUAL_LOCK)
   SIZE_T working_min = 0, working_max = 0;
   if(!::GetProcessWorkingSetSize(::GetCurrentProcess(), &working_min, &working_max))
      {
      return 0;
      }

   // According to Microsoft MSDN:
   // The maximum number of pages that a process can lock is equal to the number of pages in its minimum working set minus a small overhead
   // In the book "Windows Internals Part 2": the maximum lockable pages are minimum working set size - 8 pages
   // But the information in the book seems to be inaccurate/outdated
   // I've tested this on Windows 8.1 x64, Windows 10 x64 and Windows 7 x86
   // On all three OS the value is 11 instead of 8
   const size_t overhead = OS::system_page_size() * 11;
   if(working_min > overhead)
      {
      const size_t lockable_bytes = working_min - overhead;
      return std::min<size_t>(lockable_bytes, BOTAN_MLOCK_ALLOCATOR_MAX_LOCKED_KB * 1024);
      }
#endif

   // Not supported on this platform
   return 0;
   }

bool OS::read_env_variable(std::string& value_out, const std::string& name)
   {
   value_out = "";

   if(running_in_privileged_state())
      return false;

#if defined(BOTAN_TARGET_OS_HAS_WIN32) && defined(BOTAN_BUILD_COMPILER_IS_MSVC)
   char val[128] = { 0 };
   size_t req_size = 0;
   if(getenv_s(&req_size, val, sizeof(val), name.c_str()) == 0)
      {
      value_out = std::string(val, req_size);
      return true;
      }
#else
   if(const char* val = std::getenv(name.c_str()))
      {
      value_out = val;
      return true;
      }
#endif

   return false;
   }

size_t OS::read_env_variable_sz(const std::string& name, size_t def)
   {
   std::string value;
   if(read_env_variable(value, name))
      {
      try
         {
         const size_t val = std::stoul(value, nullptr);
         return val;
         }
      catch(std::exception&) { /* ignore it */ }
      }

   return def;
   }

#if defined(BOTAN_TARGET_OS_HAS_POSIX1) && defined(BOTAN_TARGET_OS_HAS_POSIX_MLOCK)

namespace {

int get_locked_fd()
   {
#if defined(BOTAN_TARGET_OS_IS_IOS) || defined(BOTAN_TARGET_OS_IS_MACOS)
   // On Darwin, tagging anonymous pages allows vmmap to track these.
   // Allowed from 240 to 255 for userland applications
   static constexpr int default_locked_fd = 255;
   int locked_fd = default_locked_fd;

   if(size_t locked_fdl = OS::read_env_variable_sz("BOTAN_LOCKED_FD", default_locked_fd))
      {
      if(locked_fdl < 240 || locked_fdl > 255)
         {
         locked_fdl = default_locked_fd;
         }
      locked_fd = static_cast<int>(locked_fdl);
      }
   return VM_MAKE_TAG(locked_fd);
#else
   return -1;
#endif
   }

}

#endif

std::vector<void*> OS::allocate_locked_pages(size_t count)
   {
   std::vector<void*> result;

#if (defined(BOTAN_TARGET_OS_HAS_POSIX1) && defined(BOTAN_TARGET_OS_HAS_POSIX_MLOCK)) || defined(BOTAN_TARGET_OS_HAS_VIRTUAL_LOCK)

   result.reserve(count);

   const size_t page_size = OS::system_page_size();

#if defined(BOTAN_TARGET_OS_HAS_POSIX1) && defined(BOTAN_TARGET_OS_HAS_POSIX_MLOCK)
   static const int locked_fd = get_locked_fd();
#endif

   for(size_t i = 0; i != count; ++i)
      {
      void* ptr = nullptr;

#if defined(BOTAN_TARGET_OS_HAS_POSIX1) && defined(BOTAN_TARGET_OS_HAS_POSIX_MLOCK)

#if !defined(MAP_ANONYMOUS)
   #define MAP_ANONYMOUS MAP_ANON
#endif

#if !defined(MAP_NOCORE)
#if defined(MAP_CONCEAL)
   #define MAP_NOCORE MAP_CONCEAL
#else
   #define MAP_NOCORE 0
#endif
#endif

#if !defined(PROT_MAX)
   #define PROT_MAX(p) 0
#endif
      const int pflags = PROT_READ | PROT_WRITE;

      ptr = ::mmap(nullptr, 3*page_size,
                   pflags | PROT_MAX(pflags),
                   MAP_ANONYMOUS | MAP_PRIVATE | MAP_NOCORE,
                   /*fd=*/locked_fd, /*offset=*/0);

      if(ptr == MAP_FAILED)
         {
         continue;
         }

      // lock the data page
      if(::mlock(static_cast<uint8_t*>(ptr) + page_size, page_size) != 0)
         {
         ::munmap(ptr, 3*page_size);
         continue;
         }

#if defined(MADV_DONTDUMP)
      // we ignore errors here, as DONTDUMP is just a bonus
      ::madvise(static_cast<uint8_t*>(ptr) + page_size, page_size, MADV_DONTDUMP);
#endif

#elif defined(BOTAN_TARGET_OS_HAS_VIRTUAL_LOCK)
      ptr = ::VirtualAlloc(nullptr, 3*page_size, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);

      if(ptr == nullptr)
         continue;

      if(::VirtualLock(static_cast<uint8_t*>(ptr) + page_size, page_size) == 0)
         {
         ::VirtualFree(ptr, 0, MEM_RELEASE);
         continue;
         }
#endif

      std::memset(ptr, 0, 3*page_size); // zero data page and both guard pages

      // Make guard page preceeding the data page
      page_prohibit_access(static_cast<uint8_t*>(ptr));
      // Make guard page following the data page
      page_prohibit_access(static_cast<uint8_t*>(ptr) + 2*page_size);

      result.push_back(static_cast<uint8_t*>(ptr) + page_size);
      }
#else
   BOTAN_UNUSED(count);
#endif

   return result;
   }

void OS::page_allow_access(void* page)
   {
#if defined(BOTAN_TARGET_OS_HAS_POSIX1)
   const size_t page_size = OS::system_page_size();
   ::mprotect(page, page_size, PROT_READ | PROT_WRITE);
#elif defined(BOTAN_TARGET_OS_HAS_VIRTUAL_LOCK)
   const size_t page_size = OS::system_page_size();
   DWORD old_perms = 0;
   ::VirtualProtect(page, page_size, PAGE_READWRITE, &old_perms);
   BOTAN_UNUSED(old_perms);
#else
   BOTAN_UNUSED(page);
#endif
   }

void OS::page_prohibit_access(void* page)
   {
#if defined(BOTAN_TARGET_OS_HAS_POSIX1)
   const size_t page_size = OS::system_page_size();
   ::mprotect(page, page_size, PROT_NONE);
#elif defined(BOTAN_TARGET_OS_HAS_VIRTUAL_LOCK)
   const size_t page_size = OS::system_page_size();
   DWORD old_perms = 0;
   ::VirtualProtect(page, page_size, PAGE_NOACCESS, &old_perms);
   BOTAN_UNUSED(old_perms);
#else
   BOTAN_UNUSED(page);
#endif
   }

void OS::free_locked_pages(const std::vector<void*>& pages)
   {
   const size_t page_size = OS::system_page_size();

   for(size_t i = 0; i != pages.size(); ++i)
      {
      void* ptr = pages[i];

      secure_scrub_memory(ptr, page_size);

      // ptr points to the data page, guard pages are before and after
      page_allow_access(static_cast<uint8_t*>(ptr) - page_size);
      page_allow_access(static_cast<uint8_t*>(ptr) + page_size);

#if defined(BOTAN_TARGET_OS_HAS_POSIX1) && defined(BOTAN_TARGET_OS_HAS_POSIX_MLOCK)
      ::munlock(ptr, page_size);
      ::munmap(static_cast<uint8_t*>(ptr) - page_size, 3*page_size);
#elif defined(BOTAN_TARGET_OS_HAS_VIRTUAL_LOCK)
      ::VirtualUnlock(ptr, page_size);
      ::VirtualFree(static_cast<uint8_t*>(ptr) - page_size, 0, MEM_RELEASE);
#endif
      }
   }

#if defined(BOTAN_TARGET_OS_HAS_POSIX1) && !defined(BOTAN_TARGET_OS_IS_EMSCRIPTEN)

namespace {

static ::sigjmp_buf g_sigill_jmp_buf;

void botan_sigill_handler(int)
   {
   siglongjmp(g_sigill_jmp_buf, /*non-zero return value*/1);
   }

}

#endif

int OS::run_cpu_instruction_probe(std::function<int ()> probe_fn)
   {
   volatile int probe_result = -3;

#if defined(BOTAN_TARGET_OS_HAS_POSIX1) && !defined(BOTAN_TARGET_OS_IS_EMSCRIPTEN)
   struct sigaction old_sigaction;
   struct sigaction sigaction;

   sigaction.sa_handler = botan_sigill_handler;
   sigemptyset(&sigaction.sa_mask);
   sigaction.sa_flags = 0;

   int rc = ::sigaction(SIGILL, &sigaction, &old_sigaction);

   if(rc != 0)
      throw System_Error("run_cpu_instruction_probe sigaction failed", errno);

   rc = sigsetjmp(g_sigill_jmp_buf, /*save sigs*/1);

   if(rc == 0)
      {
      // first call to sigsetjmp
      probe_result = probe_fn();
      }
   else if(rc == 1)
      {
      // non-local return from siglongjmp in signal handler: return error
      probe_result = -1;
      }

   // Restore old SIGILL handler, if any
   rc = ::sigaction(SIGILL, &old_sigaction, nullptr);
   if(rc != 0)
      throw System_Error("run_cpu_instruction_probe sigaction restore failed", errno);

#else
   BOTAN_UNUSED(probe_fn);
#endif

   return probe_result;
   }

std::unique_ptr<OS::Echo_Suppression> OS::suppress_echo_on_terminal()
   {
#if defined(BOTAN_TARGET_OS_HAS_POSIX1)
   class POSIX_Echo_Suppression : public Echo_Suppression
      {
      public:
         POSIX_Echo_Suppression()
            {
            m_stdin_fd = fileno(stdin);
            if(::tcgetattr(m_stdin_fd, &m_old_termios) != 0)
               throw System_Error("Getting terminal status failed", errno);

            struct termios noecho_flags = m_old_termios;
            noecho_flags.c_lflag &= ~ECHO;
            noecho_flags.c_lflag |= ECHONL;

            if(::tcsetattr(m_stdin_fd, TCSANOW, &noecho_flags) != 0)
               throw System_Error("Clearing terminal echo bit failed", errno);
            }

         void reenable_echo() override
            {
            if(m_stdin_fd > 0)
               {
               if(::tcsetattr(m_stdin_fd, TCSANOW, &m_old_termios) != 0)
                  throw System_Error("Restoring terminal echo bit failed", errno);
               m_stdin_fd = -1;
               }
            }

         ~POSIX_Echo_Suppression()
            {
            try
               {
               reenable_echo();
               }
            catch(...)
               {
               }
            }

      private:
         int m_stdin_fd;
         struct termios m_old_termios;
      };

   return std::unique_ptr<Echo_Suppression>(new POSIX_Echo_Suppression);

#elif defined(BOTAN_TARGET_OS_HAS_WIN32)

   class Win32_Echo_Suppression : public Echo_Suppression
      {
      public:
         Win32_Echo_Suppression()
            {
            m_input_handle = ::GetStdHandle(STD_INPUT_HANDLE);
            if(::GetConsoleMode(m_input_handle, &m_console_state) == 0)
               throw System_Error("Getting console mode failed", ::GetLastError());

            DWORD new_mode = ENABLE_LINE_INPUT | ENABLE_PROCESSED_INPUT;
            if(::SetConsoleMode(m_input_handle, new_mode) == 0)
               throw System_Error("Setting console mode failed", ::GetLastError());
            }

         void reenable_echo() override
            {
            if(m_input_handle != INVALID_HANDLE_VALUE)
               {
               if(::SetConsoleMode(m_input_handle, m_console_state) == 0)
                  throw System_Error("Setting console mode failed", ::GetLastError());
               m_input_handle = INVALID_HANDLE_VALUE;
               }
            }

         ~Win32_Echo_Suppression()
            {
            try
               {
               reenable_echo();
               }
            catch(...)
               {
               }
            }

      private:
         HANDLE m_input_handle;
         DWORD m_console_state;
      };

   return std::unique_ptr<Echo_Suppression>(new Win32_Echo_Suppression);

#else

   // Not supported on this platform, return null
   return std::unique_ptr<Echo_Suppression>();
#endif
   }

}