oemcrypto/util/test/test_sleep.cpp

// Copyright 2019 Google LLC. All Rights Reserved. This file and proprietary
// source code may only be used and distributed under the Widevine Master
// License Agreement.

#include "test_sleep.h"

#ifdef _WIN32
#  include <windows.h>
#else
#  include <sys/types.h>
#endif

#include <errno.h>
#include <string.h>
#include <unistd.h>

#include <chrono>

#include "clock.h"
#include "log.h"

namespace wvcdm {

bool TestSleep::real_sleep_ = true;
TestSleep::CallBack* TestSleep::callback_ = nullptr;
int TestSleep::total_clock_rollback_ = 0;

void TestSleep::Sleep(unsigned int seconds) {
  int64_t milliseconds = 1000 * seconds;
  if (real_sleep_) {
    // This next bit of logic is to avoid slow drift apart of the real clock and
    // the fake clock.  We compute how far from the real clock has advanced in
    // total since the start, and then compare to a running total of sleep
    // calls. We sleep for approximately x second, and then advance the clock by
    // the amount of time that has actually passed.
    static auto start_real = std::chrono::system_clock().now();
    static int64_t fake_clock = 0;
    sleep(seconds);
    auto now_real = std::chrono::system_clock().now();
    int64_t total_real = (now_real - start_real) / std::chrono::milliseconds(1);
    // We want to advance the fake clock by the difference between the real
    // clock, and the previous value on the fake clock.
    milliseconds = total_real - fake_clock;
    fake_clock += milliseconds;
  }
  if (callback_ != nullptr) callback_->ElapseTime(milliseconds);
}

void TestSleep::SyncFakeClock() {
  // Syncing can be done by sleeping 0 seconds.
  Sleep(0);
}

bool TestSleep::RollbackSystemTime(int seconds) {
  if (real_sleep_) {
#ifdef _WIN32
    // See remarks from this for why this series is used.
    // https://msdn.microsoft.com/en-us/f77cdf86-0f97-4a89-b565-95b46fa7d65b
    SYSTEMTIME time;
    GetSystemTime(&time);
    FILETIME file_time;
    if (!SystemTimeToFileTime(time, &file_time)) return false;
    uint64_t long_time =
        static_cast<uint64_t>(file_time.dwLowDateTime) |
        (static_cast<uint64_t>(file_time.dwHighDateTime) << 32);
    long_time += static_cast<uint64_t>(delta_seconds) *
                 1e7;  // long_time is in 100-nanosecond intervals.
    file_time.dwLowDateTime = long_time & ((1ull << 32) - 1);
    file_time.dwHighDateTime = long_time >> 32;
    if (!FileTimeToSystemTime(&file_time, &time)) return false;
    if (!SetSystemTime(&time)) return false;
#else
    auto time = std::chrono::system_clock::now();
    auto modified_time = time - std::chrono::seconds(seconds);
    ;
    timespec time_spec;
    time_spec.tv_sec = std::chrono::duration_cast<std::chrono::seconds>(
                           modified_time.time_since_epoch())
                           .count();
    time_spec.tv_nsec = std::chrono::duration_cast<std::chrono::nanoseconds>(
                            modified_time.time_since_epoch())
                            .count() %
                        (1000 * 1000 * 1000);
    if (clock_settime(CLOCK_REALTIME, &time_spec)) {
      LOGE("Error setting clock: %s", strerror(errno));
      return false;
    }
#endif
  }  // end if(real_sleep_)...

  // For both real and fake sleep we still update the callback and we still keep
  // track of the total amount of time slept.
  total_clock_rollback_ += seconds;
  if (callback_ != nullptr) callback_->ElapseTime(-1000 * seconds);
  return true;
}

bool TestSleep::CanChangeSystemTime() {
  // If we are using a fake clock, then we can move the clock backwards by
  // just going backwards.
  // ElapseTime.
  if (!real_sleep_) {
    return true;
  }
#ifdef _WIN32
  LUID desired_id;
  if (!LookupPrivilegeValue(nullptr, SE_SYSTEMTIME_NAME, &desired_id)) {
    LOGE("Win32 time rollback: no SYSTEMTIME permission.");
    return false;
  }
  HANDLE token;
  if (!OpenProcessToken(GetCurrentProcess(), TOKEN_ALL_ACCESS, &token)) {
    LOGE("Win32 time rollback: cannot access process token.");
    return false;
  }
  std::unique_ptr<void, decltype(&CloseHandle)> safe_token(token, &CloseHandle);

  // This queries all the permissions given to the token to determine if we can
  // change the system time.  Note this is subtly different from PrivilegeCheck
  // as that only checks "enabled" privileges; even with admin rights, the
  // privilege is default disabled, even when granted.

  DWORD size = 0;
  // Determine how big we need to allocate first.
  GetTokenInformation(token, TokenPrivileges, nullptr, 0, &size);
  // Since TOKEN_PRIVILEGES uses a variable-length array, we need to use malloc
  std::unique_ptr<TOKEN_PRIVILEGES, decltype(&free)> privileges(
      (TOKEN_PRIVILEGES*)malloc(size), &free);
  if (privileges && GetTokenInformation(token, TokenPrivileges,
                                        privileges.get(), size, &size)) {
    for (int i = 0; i < privileges->PrivilegeCount; i++) {
      if (privileges->Privileges[i].Luid.HighPart == desired_id.HighPart &&
          privileges->Privileges[i].Luid.LowPart == desired_id.LowPart) {
        return true;
      }
    }
  }
  LOGE("Win32 time rollback: cannot set system time.");
  return false;
#else
  // Otherwise, the test needs to be run as root.
  const uid_t uid = getuid();
  if (uid == 0) return true;
  LOGE("Unix time rollback: not running as root (uid=%u.", uid);
  return false;
#endif
}
}  // namespace wvcdm