/*

* 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/internal/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_AUXINFO)

  #include <dlfcn.h>

  #include <elf.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 <sys/types.h>

  #include <sys/sysctl.h>

  #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

   }

size_t OS::get_cache_line_size()

   {

#if defined(BOTAN_TARGET_OS_IS_IOS) || defined(BOTAN_TARGET_OS_IS_MACOS)

   unsigned long cache_line_size_vl;

   size_t size = sizeof(cache_line_size_vl);

   if(::sysctlbyname("hw.cachelinesize", &cache_line_size_vl, &size, nullptr, 0) == 0)

      return static_cast<size_t>(cache_line_size_vl);

#endif

#if defined(BOTAN_TARGET_OS_HAS_POSIX1) && defined(_SC_LEVEL1_DCACHE_LINESIZE)

   const long res = ::sysconf(_SC_LEVEL1_DCACHE_LINESIZE);

   if(res > 0)

      return static_cast<size_t>(res);

#endif

#if defined(BOTAN_TARGET_OS_HAS_GETAUXVAL)

   #if defined(AT_L1D_CACHEGEOMETRY)

   // Cache line size is bottom 16 bits

   const unsigned long dcache_info = OS::get_auxval(AT_L1D_CACHEGEOMETRY);

   if(dcache_info != 0)

      return static_cast<size_t>(dcache_info & 0xFFFF);

   #endif

   #if defined(AT_DCACHEBSIZE)

   const unsigned long dcache_bsize = OS::get_auxval(AT_DCACHEBSIZE);

   if(dcache_bsize != 0)

      return static_cast<size_t>(dcache_bsize);

   #endif

#endif

   // TODO: on Windows this is returned by GetLogicalProcessorInformation

   // not available on this platform

   return 0;

   }

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(static_cast<int>(id), &auxinfo, sizeof(auxinfo));

   return auxinfo;

#elif defined(BOTAN_TARGET_OS_HAS_AUXINFO)

   for (const AuxInfo *auxinfo = static_cast<AuxInfo *>(::_dlauxinfo()); auxinfo != AT_NULL; ++auxinfo)

      {

      if (id == auxinfo->a_type)

          return auxinfo->a_v;

      }

   return 0;

#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?

#elif defined(BOTAN_TARGET_ARCH_IS_ARM64) && defined(BOTAN_TARGET_OS_IS_MACOS)

   asm volatile("isb; mrs %0, cntvct_el0" : "=r" (rtc));

#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

   }

}