/* This is a maximally equidistributed combined Tausworthe generator based on code from GNU Scientific Library 1.5 (30 Jun 2004) lfsr113 version: x_n = (s1_n ^ s2_n ^ s3_n ^ s4_n) s1_{n+1} = (((s1_n & 4294967294) << 18) ^ (((s1_n << 6) ^ s1_n) >> 13)) s2_{n+1} = (((s2_n & 4294967288) << 2) ^ (((s2_n << 2) ^ s2_n) >> 27)) s3_{n+1} = (((s3_n & 4294967280) << 7) ^ (((s3_n << 13) ^ s3_n) >> 21)) s4_{n+1} = (((s4_n & 4294967168) << 13) ^ (((s4_n << 3) ^ s4_n) >> 12)) The period of this generator is about 2^113 (see erratum paper). From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe Generators", Mathematics of Computation, 65, 213 (1996), 203--213: http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps There is an erratum in the paper "Tables of Maximally Equidistributed Combined LFSR Generators", Mathematics of Computation, 68, 225 (1999), 261--269: http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps ... the k_j most significant bits of z_j must be non- zero, for each j. (Note: this restriction also applies to the computer code given in [4], but was mistakenly not mentioned in that paper.) This affects the seeding procedure by imposing the requirement s1 > 1, s2 > 7, s3 > 15, s4 > 127. */ #include #include #include #include #include static DEFINE_PER_CPU(struct rnd_state, net_rand_state); /** * prandom_u32_state - seeded pseudo-random number generator. * @state: pointer to state structure holding seeded state. * * This is used for pseudo-randomness with no outside seeding. * For more random results, use prandom_u32(). */ u32 prandom_u32_state(struct rnd_state *state) { #define TAUSWORTHE(s,a,b,c,d) ((s&c)<>b) state->s1 = TAUSWORTHE(state->s1, 6U, 13U, 4294967294U, 18U); state->s2 = TAUSWORTHE(state->s2, 2U, 27U, 4294967288U, 2U); state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U, 7U); state->s4 = TAUSWORTHE(state->s4, 3U, 12U, 4294967168U, 13U); return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4); } EXPORT_SYMBOL(prandom_u32_state); /** * prandom_u32 - pseudo random number generator * * A 32 bit pseudo-random number is generated using a fast * algorithm suitable for simulation. This algorithm is NOT * considered safe for cryptographic use. */ u32 prandom_u32(void) { unsigned long r; struct rnd_state *state = &get_cpu_var(net_rand_state); r = prandom_u32_state(state); put_cpu_var(state); return r; } EXPORT_SYMBOL(prandom_u32); /* * prandom_bytes_state - get the requested number of pseudo-random bytes * * @state: pointer to state structure holding seeded state. * @buf: where to copy the pseudo-random bytes to * @bytes: the requested number of bytes * * This is used for pseudo-randomness with no outside seeding. * For more random results, use prandom_bytes(). */ void prandom_bytes_state(struct rnd_state *state, void *buf, int bytes) { unsigned char *p = buf; int i; for (i = 0; i < round_down(bytes, sizeof(u32)); i += sizeof(u32)) { u32 random = prandom_u32_state(state); int j; for (j = 0; j < sizeof(u32); j++) { p[i + j] = random; random >>= BITS_PER_BYTE; } } if (i < bytes) { u32 random = prandom_u32_state(state); for (; i < bytes; i++) { p[i] = random; random >>= BITS_PER_BYTE; } } } EXPORT_SYMBOL(prandom_bytes_state); /** * prandom_bytes - get the requested number of pseudo-random bytes * @buf: where to copy the pseudo-random bytes to * @bytes: the requested number of bytes */ void prandom_bytes(void *buf, int bytes) { struct rnd_state *state = &get_cpu_var(net_rand_state); prandom_bytes_state(state, buf, bytes); put_cpu_var(state); } EXPORT_SYMBOL(prandom_bytes); static void prandom_warmup(struct rnd_state *state) { /* Calling RNG ten times to satify recurrence condition */ prandom_u32_state(state); prandom_u32_state(state); prandom_u32_state(state); prandom_u32_state(state); prandom_u32_state(state); prandom_u32_state(state); prandom_u32_state(state); prandom_u32_state(state); prandom_u32_state(state); prandom_u32_state(state); } /** * prandom_seed - add entropy to pseudo random number generator * @seed: seed value * * Add some additional seeding to the prandom pool. */ void prandom_seed(u32 entropy) { int i; /* * No locking on the CPUs, but then somewhat random results are, well, * expected. */ for_each_possible_cpu (i) { struct rnd_state *state = &per_cpu(net_rand_state, i); state->s1 = __seed(state->s1 ^ entropy, 2U); prandom_warmup(state); } } EXPORT_SYMBOL(prandom_seed); /* * Generate some initially weak seeding values to allow * to start the prandom_u32() engine. */ static int __init prandom_init(void) { int i; for_each_possible_cpu(i) { struct rnd_state *state = &per_cpu(net_rand_state,i); #define LCG(x) ((x) * 69069U) /* super-duper LCG */ state->s1 = __seed(LCG((i + jiffies) ^ random_get_entropy()), 2U); state->s2 = __seed(LCG(state->s1), 8U); state->s3 = __seed(LCG(state->s2), 16U); state->s4 = __seed(LCG(state->s3), 128U); prandom_warmup(state); } return 0; } core_initcall(prandom_init); static void __prandom_timer(unsigned long dontcare); static DEFINE_TIMER(seed_timer, __prandom_timer, 0, 0); static void __prandom_timer(unsigned long dontcare) { u32 entropy; get_random_bytes(&entropy, sizeof(entropy)); prandom_seed(entropy); /* reseed every ~60 seconds, in [40 .. 80) interval with slack */ seed_timer.expires = jiffies + (40 * HZ + (prandom_u32() % (40 * HZ))); add_timer(&seed_timer); } static void prandom_start_seed_timer(void) { set_timer_slack(&seed_timer, HZ); seed_timer.expires = jiffies + 40 * HZ; add_timer(&seed_timer); } /* * Generate better values after random number generator * is fully initialized. */ static void __prandom_reseed(bool late) { int i; unsigned long flags; static bool latch = false; static DEFINE_SPINLOCK(lock); /* only allow initial seeding (late == false) once */ spin_lock_irqsave(&lock, flags); if (latch && !late) goto out; latch = true; for_each_possible_cpu(i) { struct rnd_state *state = &per_cpu(net_rand_state,i); u32 seeds[4]; get_random_bytes(&seeds, sizeof(seeds)); state->s1 = __seed(seeds[0], 2U); state->s2 = __seed(seeds[1], 8U); state->s3 = __seed(seeds[2], 16U); state->s4 = __seed(seeds[3], 128U); prandom_warmup(state); } out: spin_unlock_irqrestore(&lock, flags); } void prandom_reseed_late(void) { __prandom_reseed(true); } static int __init prandom_reseed(void) { __prandom_reseed(false); prandom_start_seed_timer(); return 0; } late_initcall(prandom_reseed);