Function DetermineDevShmExecutable

src/butil/file_util_posix.cc:163–182

Determine if /dev/shm files can be mapped and then mprotect'd PROT_EXEC. This depends on the mount options used for /dev/shm, which vary among different Linux distributions and possibly local configuration. It also depends on details of kernel--ChromeOS uses the noexec option for /dev/shm but its kernel allows mprotect with PROT_EXEC anyway.

// depends on details of kernel--ChromeOS uses the noexec option for /dev/shm
// but its kernel allows mprotect with PROT_EXEC anyway.
bool DetermineDevShmExecutable() {
  bool result = false;
  FilePath path;

  ScopedFD fd(CreateAndOpenFdForTemporaryFile(FilePath("/dev/shm"), &path));
  if (fd.is_valid()) {
    DeleteFile(path, false);
    long sysconf_result = sysconf(_SC_PAGESIZE);
    CHECK_GE(sysconf_result, 0);
    size_t pagesize = static_cast<size_t>(sysconf_result);
    CHECK_GE(sizeof(pagesize), sizeof(sysconf_result));
    void* mapping = mmap(NULL, pagesize, PROT_READ, MAP_SHARED, fd.get(), 0);
    if (mapping != MAP_FAILED) {
      if (mprotect(mapping, pagesize, PROT_READ | PROT_EXEC) == 0)
        result = true;
      munmap(mapping, pagesize);
    }
  }
  return result;
}
#endif  // defined(OS_LINUX)

}  // namespace