linux/kernel/seccomp.c
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   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 */
  20static 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
  26static 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
  32void __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
  59long prctl_get_seccomp(void)
  60{
  61        return current->seccomp.mode;
  62}
  63
  64long 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}
  86
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