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
__secure_computing(int this_syscall)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
prctl_get_seccomp(void)60 long prctl_get_seccomp(void)
61 {
62 return current->seccomp.mode;
63 }
64
prctl_set_seccomp(unsigned long seccomp_mode)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 }
87