1 /*
2 ** Pseudo-random number generation.
3 ** Copyright (C) 2005-2021 Mike Pall. See Copyright Notice in luajit.h
4 */
5
6 #define lj_prng_c
7 #define LUA_CORE
8
9 /* To get the syscall prototype. */
10 #if defined(__linux__) && !defined(_GNU_SOURCE)
11 #define _GNU_SOURCE
12 #endif
13
14 #include "lj_def.h"
15 #include "lj_arch.h"
16 #include "lj_prng.h"
17
18 /* -- PRNG step function -------------------------------------------------- */
19
20 /* This implements a Tausworthe PRNG with period 2^223. Based on:
21 ** Tables of maximally-equidistributed combined LFSR generators,
22 ** Pierre L'Ecuyer, 1991, table 3, 1st entry.
23 ** Full-period ME-CF generator with L=64, J=4, k=223, N1=49.
24 **
25 ** Important note: This PRNG is NOT suitable for cryptographic use!
26 **
27 ** But it works fine for math.random(), which has an API that's not
28 ** suitable for cryptography, anyway.
29 **
30 ** When used as a securely seeded global PRNG, it substantially raises
31 ** the difficulty for various attacks on the VM.
32 */
33
34 /* Update generator i and compute a running xor of all states. */
35 #define TW223_GEN(rs, z, r, i, k, q, s) \
36 z = rs->u[i]; \
37 z = (((z<<q)^z) >> (k-s)) ^ ((z&((uint64_t)(int64_t)-1 << (64-k)))<<s); \
38 r ^= z; rs->u[i] = z;
39
40 #define TW223_STEP(rs, z, r) \
41 TW223_GEN(rs, z, r, 0, 63, 31, 18) \
42 TW223_GEN(rs, z, r, 1, 58, 19, 28) \
43 TW223_GEN(rs, z, r, 2, 55, 24, 7) \
44 TW223_GEN(rs, z, r, 3, 47, 21, 8)
45
46 /* PRNG step function with uint64_t result. */
lj_prng_u64(PRNGState * rs)47 LJ_NOINLINE uint64_t LJ_FASTCALL lj_prng_u64(PRNGState *rs)
48 {
49 uint64_t z, r = 0;
50 TW223_STEP(rs, z, r)
51 return r;
52 }
53
54 /* PRNG step function with double in uint64_t result. */
lj_prng_u64d(PRNGState * rs)55 LJ_NOINLINE uint64_t LJ_FASTCALL lj_prng_u64d(PRNGState *rs)
56 {
57 uint64_t z, r = 0;
58 TW223_STEP(rs, z, r)
59 /* Returns a double bit pattern in the range 1.0 <= d < 2.0. */
60 return (r & U64x(000fffff,ffffffff)) | U64x(3ff00000,00000000);
61 }
62
63 /* Condition seed: ensure k[i] MSB of u[i] are non-zero. */
lj_prng_condition(PRNGState * rs)64 static LJ_AINLINE void lj_prng_condition(PRNGState *rs)
65 {
66 if (rs->u[0] < (1u << 1)) rs->u[0] += (1u << 1);
67 if (rs->u[1] < (1u << 6)) rs->u[1] += (1u << 6);
68 if (rs->u[2] < (1u << 9)) rs->u[2] += (1u << 9);
69 if (rs->u[3] < (1u << 17)) rs->u[3] += (1u << 17);
70 }
71
72 /* -- PRNG seeding from OS ------------------------------------------------ */
73
74 #if LUAJIT_SECURITY_PRNG == 0
75
76 /* Nothing to define. */
77
78 #elif LJ_TARGET_XBOX360
79
80 extern int XNetRandom(void *buf, unsigned int len);
81
82 #elif LJ_TARGET_PS3
83
84 extern int sys_get_random_number(void *buf, uint64_t len);
85
86 #elif LJ_TARGET_PS4 || LJ_TARGET_PSVITA
87
88 extern int sceRandomGetRandomNumber(void *buf, size_t len);
89
90 #elif LJ_TARGET_WINDOWS || LJ_TARGET_XBOXONE
91
92 #define WIN32_LEAN_AND_MEAN
93 #include <windows.h>
94
95 #if LJ_TARGET_UWP || LJ_TARGET_XBOXONE
96 /* Must use BCryptGenRandom. */
97 #include <bcrypt.h>
98 #pragma comment(lib, "bcrypt.lib")
99 #else
100 /* If you wonder about this mess, then search online for RtlGenRandom. */
101 typedef BOOLEAN (WINAPI *PRGR)(void *buf, ULONG len);
102 static PRGR libfunc_rgr;
103 #endif
104
105 #elif LJ_TARGET_POSIX
106
107 #if LJ_TARGET_LINUX
108 /* Avoid a dependency on glibc 2.25+ and use the getrandom syscall instead. */
109 #include <sys/syscall.h>
110 #else
111
112 #ifndef LJ_TARGET_HAS_GETENTROPY
113 #if LJ_TARGET_OSX && !LJ_TARGET_IOS
114 /*
115 ** In their infinite wisdom Apple decided to disallow getentropy() in the
116 ** iOS App Store. Even though the call is common to all BSD-ish OS, it's
117 ** recommended by Apple in their own security-related docs, and, to top
118 ** off the foolery, /dev/urandom is handled by the same kernel code,
119 ** yet accessing it is actually permitted (but less efficient).
120 */
121 #include <Availability.h>
122 #if __MAC_OS_X_VERSION_MIN_REQUIRED >= 101200
123 #define LJ_TARGET_HAS_GETENTROPY 1
124 #endif
125 #elif (LJ_TARGET_BSD && !defined(__NetBSD__)) || LJ_TARGET_SOLARIS || LJ_TARGET_CYGWIN
126 #define LJ_TARGET_HAS_GETENTROPY 1
127 #endif
128 #endif
129
130 #if LJ_TARGET_HAS_GETENTROPY
131 extern int getentropy(void *buf, size_t len);
132 #ifdef __ELF__
133 __attribute__((weak))
134 #endif
135 ;
136 #endif
137
138 #endif
139
140 /* For the /dev/urandom fallback. */
141 #include <fcntl.h>
142 #include <unistd.h>
143
144 #endif
145
146 #if LUAJIT_SECURITY_PRNG == 0
147
148 /* If you really don't care about security, then define
149 ** LUAJIT_SECURITY_PRNG=0. This yields a predictable seed
150 ** and provides NO SECURITY against various attacks on the VM.
151 **
152 ** BTW: This is NOT the way to get predictable table iteration,
153 ** predictable trace generation, predictable bytecode generation, etc.
154 */
lj_prng_seed_secure(PRNGState * rs)155 int LJ_FASTCALL lj_prng_seed_secure(PRNGState *rs)
156 {
157 lj_prng_seed_fixed(rs); /* The fixed seed is already conditioned. */
158 return 1;
159 }
160
161 #else
162
163 /* Securely seed PRNG from system entropy. Returns 0 on failure. */
lj_prng_seed_secure(PRNGState * rs)164 int LJ_FASTCALL lj_prng_seed_secure(PRNGState *rs)
165 {
166 #if LJ_TARGET_XBOX360
167
168 if (XNetRandom(rs->u, (unsigned int)sizeof(rs->u)) == 0)
169 goto ok;
170
171 #elif LJ_TARGET_PS3
172
173 if (sys_get_random_number(rs->u, sizeof(rs->u)) == 0)
174 goto ok;
175
176 #elif LJ_TARGET_PS4 || LJ_TARGET_PSVITA
177
178 if (sceRandomGetRandomNumber(rs->u, sizeof(rs->u)) == 0)
179 goto ok;
180
181 #elif LJ_TARGET_UWP || LJ_TARGET_XBOXONE
182
183 if (BCryptGenRandom(NULL, (PUCHAR)(rs->u), (ULONG)sizeof(rs->u),
184 BCRYPT_USE_SYSTEM_PREFERRED_RNG) >= 0)
185 goto ok;
186
187 #elif LJ_TARGET_WINDOWS
188
189 /* Keep the library loaded in case multiple VMs are started. */
190 if (!libfunc_rgr) {
191 HMODULE lib = LJ_WIN_LOADLIBA("advapi32.dll");
192 if (!lib) return 0;
193 libfunc_rgr = (PRGR)GetProcAddress(lib, "SystemFunction036");
194 if (!libfunc_rgr) return 0;
195 }
196 if (libfunc_rgr(rs->u, (ULONG)sizeof(rs->u)))
197 goto ok;
198
199 #elif LJ_TARGET_POSIX
200
201 #if LJ_TARGET_LINUX && defined(SYS_getrandom)
202
203 if (syscall(SYS_getrandom, rs->u, sizeof(rs->u), 0) == (long)sizeof(rs->u))
204 goto ok;
205
206 #elif LJ_TARGET_HAS_GETENTROPY
207
208 #ifdef __ELF__
209 if (&getentropy && getentropy(rs->u, sizeof(rs->u)) == 0)
210 goto ok;
211 #else
212 if (getentropy(rs->u, sizeof(rs->u)) == 0)
213 goto ok;
214 #endif
215
216 #endif
217
218 /* Fallback to /dev/urandom. This may fail if the device is not
219 ** existent or accessible in a chroot or container, or if the process
220 ** or the OS ran out of file descriptors.
221 */
222 {
223 int fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC);
224 if (fd != -1) {
225 ssize_t n = read(fd, rs->u, sizeof(rs->u));
226 (void)close(fd);
227 if (n == (ssize_t)sizeof(rs->u))
228 goto ok;
229 }
230 }
231
232 #else
233
234 /* Add an elif above for your OS with a secure PRNG seed.
235 ** Note that fiddling around with rand(), getpid(), time() or coercing
236 ** ASLR to yield a few bits of randomness is not helpful.
237 ** If you don't want any security, then don't pretend you have any
238 ** and simply define LUAJIT_SECURITY_PRNG=0 for the build.
239 */
240 #error "Missing secure PRNG seed for this OS"
241
242 #endif
243 return 0; /* Fail. */
244
245 ok:
246 lj_prng_condition(rs);
247 (void)lj_prng_u64(rs);
248 return 1; /* Success. */
249 }
250
251 #endif
252
253