kernel/seccomp.c

   1 /*
   2  * linux/kernel/seccomp.c
   3  *
   4  * Copyright 2004-2005  Andrea Arcangeli <andrea@cpushare.com>
   5  *
   6  * This defines a simple but solid secure-computing mode.
   7  */
   8
   9 #include <linux/seccomp.h>
  10 #include <linux/sched.h>
  11 #include <linux/compat.h>
  12
  13 /* #define SECCOMP_DEBUG 1 */
  14 #define NR_SECCOMP_MODES 1
  15
  16 /*
  17  * Secure computing mode 1 allows only read/write/exit/sigreturn.
  18  * To be fully secure this must be combined with rlimit
  19  * to limit the stack allocations too.
  20  */
  21 static int mode1_syscalls[] = {
  22         __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
  23         0, /* null terminated */
  24 };
  25
  26 #ifdef CONFIG_COMPAT
  27 static int mode1_syscalls_32[] = {
  28         __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
  29         0, /* null terminated */
  30 };
  31 #endif
  32
  33 void __secure_computing(int this_syscall)
  34 {
  35         int mode = current->seccomp.mode;
  36         int * syscall;
  37
  38         switch (mode) {
  39         case 1:
  40                 syscall = mode1_syscalls;
  41 #ifdef CONFIG_COMPAT
  42                 if (is_compat_task())
  43                         syscall = mode1_syscalls_32;
  44 #endif
  45                 do {
  46                         if (*syscall == this_syscall)
  47                                 return;
  48                 } while (*++syscall);
  49                 break;
  50         default:
  51                 BUG();
  52         }
  53
  54 #ifdef SECCOMP_DEBUG
  55         dump_stack();
  56 #endif
  57         do_exit(SIGKILL);
  58 }
  59
  60 long prctl_get_seccomp(void)
  61 {
  62         return current->seccomp.mode;
  63 }
  64
  65 long prctl_set_seccomp(unsigned long seccomp_mode)
  66 {
  67         long ret;
  68
  69         /* can set it only once to be even more secure */
  70         ret = -EPERM;
  71         if (unlikely(current->seccomp.mode))
  72                 goto out;
  73
  74         ret = -EINVAL;
  75         if (seccomp_mode && seccomp_mode <= NR_SECCOMP_MODES) {
  76                 current->seccomp.mode = seccomp_mode;
  77                 set_thread_flag(TIF_SECCOMP);
  78 #ifdef TIF_NOTSC
  79                 disable_TSC();
  80 #endif
  81                 ret = 0;
  82         }
  83
  84  out:
  85         return ret;
  86 }