/*
   * linux/kernel/seccomp.c
   *
   * Copyright 2004-2005  Andrea Arcangeli <andrea@cpushare.com>
   *
   * This defines a simple but solid secure-computing mode.
   */
  
  #include <linux/seccomp.h>
  #include <linux/sched.h>
  
  /* #define SECCOMP_DEBUG 1 */

  #define NR_SECCOMP_MODES 1

  
  /*
   * Secure computing mode 1 allows only read/write/exit/sigreturn.
   * To be fully secure this must be combined with rlimit
   * to limit the stack allocations too.
   */
  static int mode1_syscalls[] = {
  	__NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
  	0, /* null terminated */
  };
  
  #ifdef TIF_32BIT
  static int mode1_syscalls_32[] = {
  	__NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
  	0, /* null terminated */
  };
  #endif
  
  void __secure_computing(int this_syscall)
  {
  	int mode = current->seccomp.mode;
  	int * syscall;
  
  	switch (mode) {
  	case 1:
  		syscall = mode1_syscalls;
  #ifdef TIF_32BIT
  		if (test_thread_flag(TIF_32BIT))
  			syscall = mode1_syscalls_32;
  #endif
  		do {
  			if (*syscall == this_syscall)
  				return;
  		} while (*++syscall);
  		break;
  	default:
  		BUG();
  	}
  
  #ifdef SECCOMP_DEBUG
  	dump_stack();
  #endif
  	do_exit(SIGKILL);
  }

  
  long prctl_get_seccomp(void)
  {
  	return current->seccomp.mode;
  }
  
  long prctl_set_seccomp(unsigned long seccomp_mode)
  {
  	long ret;
  
  	/* can set it only once to be even more secure */
  	ret = -EPERM;
  	if (unlikely(current->seccomp.mode))
  		goto out;
  
  	ret = -EINVAL;
  	if (seccomp_mode && seccomp_mode <= NR_SECCOMP_MODES) {
  		current->seccomp.mode = seccomp_mode;
  		set_thread_flag(TIF_SECCOMP);

  #ifdef TIF_NOTSC
  		disable_TSC();
  #endif

  		ret = 0;
  	}
  
   out:
  	return ret;
  }