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
  12 /* #define SECCOMP_DEBUG 1 */
  13 #define NR_SECCOMP_MODES 1
  14
  15 /*
  16  * Secure computing mode 1 allows only read/write/exit/sigreturn.
  17  * To be fully secure this must be combined with rlimit
  18  * to limit the stack allocations too.
  19  */
  20 static int mode1_syscalls[] = {
  21         __NR_seccomp_read, __NR_seccomp_write, __NR_seccomp_exit, __NR_seccomp_sigreturn,
  22         0, /* null terminated */
  23 };
  24
  25 #ifdef TIF_32BIT
  26 static int mode1_syscalls_32[] = {
  27         __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
  28         0, /* null terminated */
  29 };
  30 #endif
  31
  32 void __secure_computing(int this_syscall)
  33 {
  34         int mode = current->seccomp.mode;
  35         int * syscall;
  36
  37         switch (mode) {
  38         case 1:
  39                 syscall = mode1_syscalls;
  40 #ifdef TIF_32BIT
  41                 if (test_thread_flag(TIF_32BIT))
  42                         syscall = mode1_syscalls_32;
  43 #endif
  44                 do {
  45                         if (*syscall == this_syscall)
  46                                 return;
  47                 } while (*++syscall);
  48                 break;
  49         default:
  50                 BUG();
  51         }
  52
  53 #ifdef SECCOMP_DEBUG
  54         dump_stack();
  55 #endif
  56         do_exit(SIGKILL);
  57 }
  58
  59 long prctl_get_seccomp(void)
  60 {
  61         return current->seccomp.mode;
  62 }
  63
  64 long prctl_set_seccomp(unsigned long seccomp_mode)
  65 {
  66         long ret;
  67
  68         /* can set it only once to be even more secure */
  69         ret = -EPERM;
  70         if (unlikely(current->seccomp.mode))
  71                 goto out;
  72
  73         ret = -EINVAL;
  74         if (seccomp_mode && seccomp_mode <= NR_SECCOMP_MODES) {
  75                 current->seccomp.mode = seccomp_mode;
  76                 set_thread_flag(TIF_SECCOMP);
  77 #ifdef TIF_NOTSC
  78                 disable_TSC();
  79 #endif
  80                 ret = 0;
  81         }
  82
  83  out:
  84         return ret;
  85 }