6 #include <sys/kernel.h>
7 #include <sys/random.h>
8 #include <sys/sysctl.h>
10 #include <sys/libkern.h>
12 long __stack_chk_guard[8] = {};
13 void __stack_chk_fail(void);
16 * XXX This default is unsafe!!! We intend to change it after resolving issues
17 * with early entropy in the installer; some kinds of systems that do not use
18 * loader(8), such as riscv, aarch64, and power; and perhaps others that I am
19 * forgetting off the top of my head.
21 static bool permit_nonrandom_cookies = true;
23 SYSCTL_NODE(_security, OID_AUTO, stack_protect, CTLFLAG_RW, 0,
24 "-fstack-protect support");
25 SYSCTL_BOOL(_security_stack_protect, OID_AUTO, permit_nonrandom_cookies,
26 CTLFLAG_RDTUN, &permit_nonrandom_cookies, 0,
27 "Allow stack guard to be used without real random cookies");
30 __stack_chk_fail(void)
33 panic("stack overflow detected; backtrace may be corrupted");
37 __stack_chk_init(void *dummy __unused)
40 long guard[nitems(__stack_chk_guard)];
42 if (is_random_seeded()) {
43 arc4rand(guard, sizeof(guard), 0);
44 for (i = 0; i < nitems(guard); i++)
45 __stack_chk_guard[i] = guard[i];
49 if (permit_nonrandom_cookies) {
50 printf("%s: WARNING: Initializing stack protection with "
51 "non-random cookies!\n", __func__);
52 printf("%s: WARNING: This severely limits the benefit of "
53 "-fstack-protector!\n", __func__);
56 * The emperor is naked, but I rolled some dice and at least
57 * these values aren't zero.
59 __stack_chk_guard[0] = (long)0xe7318d5959af899full;
60 __stack_chk_guard[1] = (long)0x35a9481c089348bfull;
61 __stack_chk_guard[2] = (long)0xde657fdc04117255ull;
62 __stack_chk_guard[3] = (long)0x0dd44c61c22e4a6bull;
63 __stack_chk_guard[4] = (long)0x0a5869a354edb0a5ull;
64 __stack_chk_guard[5] = (long)0x05cebfed255b5232ull;
65 __stack_chk_guard[6] = (long)0x270ffac137c4c72full;
66 __stack_chk_guard[7] = (long)0xd8141a789bad478dull;
67 _Static_assert(nitems(__stack_chk_guard) == 8,
68 "__stack_chk_guard doesn't have 8 items");
72 panic("%s: cannot initialize stack cookies because random device is "
73 "not yet seeded", __func__);
75 SYSINIT(stack_chk, SI_SUB_RANDOM, SI_ORDER_ANY, __stack_chk_init, NULL);