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random32.c has two random number generators in it: one that is meant to be used deterministically, with some predefined seed, and one that does the same exact thing as random.c, except does it poorly. The first one has some use cases. The second one no longer does and can be replaced with calls to random.c's proper random number generator. The relatively recent siphash-based bad random32.c code was added in response to concerns that the prior random32.c was too deterministic. Out of fears that random.c was (at the time) too slow, this code was anonymously contributed. Then out of that emerged a kind of shadow entropy gathering system, with its own tentacles throughout various net code, added willy nilly. Stop👏making👏bespoke👏random👏number👏generators👏. Fortunately, recent advances in random.c mean that we can stop playing with this sketchiness, and just use get_random_u32(), which is now fast enough. In micro benchmarks using RDPMC, I'm seeing the same median cycle count between the two functions, with the mean being _slightly_ higher due to batches refilling (which we can optimize further need be). However, when doing *real* benchmarks of the net functions that actually use these random numbers, the mean cycles actually *decreased* slightly (with the median still staying the same), likely because the additional prandom code means icache misses and complexity, whereas random.c is generally already being used by something else nearby. The biggest benefit of this is that there are many users of prandom who probably should be using cryptographically secure random numbers. This makes all of those accidental cases become secure by just flipping a switch. Later on, we can do a tree-wide cleanup to remove the static inline wrapper functions that this commit adds. There are also some low-ish hanging fruits for making this even faster in the future: a get_random_u16() function for use in the networking stack will give a 2x performance boost there, using SIMD for ChaCha20 will let us compute 4 or 8 or 16 blocks of output in parallel, instead of just one, giving us large buffers for cheap, and introducing a get_random_*_bh() function that assumes irqs are already disabled will shave off a few cycles for ordinary calls. These are things we can chip away at down the road. Acked-by: Jakub Kicinski <kuba@kernel.org> Acked-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
300 lines
9.1 KiB
C
300 lines
9.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* This is a maximally equidistributed combined Tausworthe generator
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* based on code from GNU Scientific Library 1.5 (30 Jun 2004)
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*
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* lfsr113 version:
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*
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* x_n = (s1_n ^ s2_n ^ s3_n ^ s4_n)
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*
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* s1_{n+1} = (((s1_n & 4294967294) << 18) ^ (((s1_n << 6) ^ s1_n) >> 13))
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* s2_{n+1} = (((s2_n & 4294967288) << 2) ^ (((s2_n << 2) ^ s2_n) >> 27))
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* s3_{n+1} = (((s3_n & 4294967280) << 7) ^ (((s3_n << 13) ^ s3_n) >> 21))
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* s4_{n+1} = (((s4_n & 4294967168) << 13) ^ (((s4_n << 3) ^ s4_n) >> 12))
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*
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* The period of this generator is about 2^113 (see erratum paper).
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*
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* From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe
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* Generators", Mathematics of Computation, 65, 213 (1996), 203--213:
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* http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps
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* ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps
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*
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* There is an erratum in the paper "Tables of Maximally Equidistributed
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* Combined LFSR Generators", Mathematics of Computation, 68, 225 (1999),
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* 261--269: http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps
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*
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* ... the k_j most significant bits of z_j must be non-zero,
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* for each j. (Note: this restriction also applies to the
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* computer code given in [4], but was mistakenly not mentioned
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* in that paper.)
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*
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* This affects the seeding procedure by imposing the requirement
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* s1 > 1, s2 > 7, s3 > 15, s4 > 127.
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*/
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#include <linux/types.h>
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#include <linux/percpu.h>
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#include <linux/export.h>
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#include <linux/jiffies.h>
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#include <linux/random.h>
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#include <linux/sched.h>
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#include <linux/bitops.h>
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#include <linux/slab.h>
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#include <asm/unaligned.h>
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/**
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* prandom_u32_state - seeded pseudo-random number generator.
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* @state: pointer to state structure holding seeded state.
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*
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* This is used for pseudo-randomness with no outside seeding.
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* For more random results, use prandom_u32().
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*/
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u32 prandom_u32_state(struct rnd_state *state)
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{
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#define TAUSWORTHE(s, a, b, c, d) ((s & c) << d) ^ (((s << a) ^ s) >> b)
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state->s1 = TAUSWORTHE(state->s1, 6U, 13U, 4294967294U, 18U);
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state->s2 = TAUSWORTHE(state->s2, 2U, 27U, 4294967288U, 2U);
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state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U, 7U);
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state->s4 = TAUSWORTHE(state->s4, 3U, 12U, 4294967168U, 13U);
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return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
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}
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EXPORT_SYMBOL(prandom_u32_state);
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/**
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* prandom_bytes_state - get the requested number of pseudo-random bytes
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*
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* @state: pointer to state structure holding seeded state.
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* @buf: where to copy the pseudo-random bytes to
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* @bytes: the requested number of bytes
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*
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* This is used for pseudo-randomness with no outside seeding.
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* For more random results, use prandom_bytes().
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*/
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void prandom_bytes_state(struct rnd_state *state, void *buf, size_t bytes)
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{
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u8 *ptr = buf;
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while (bytes >= sizeof(u32)) {
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put_unaligned(prandom_u32_state(state), (u32 *) ptr);
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ptr += sizeof(u32);
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bytes -= sizeof(u32);
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}
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if (bytes > 0) {
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u32 rem = prandom_u32_state(state);
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do {
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*ptr++ = (u8) rem;
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bytes--;
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rem >>= BITS_PER_BYTE;
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} while (bytes > 0);
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}
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}
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EXPORT_SYMBOL(prandom_bytes_state);
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static void prandom_warmup(struct rnd_state *state)
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{
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/* Calling RNG ten times to satisfy recurrence condition */
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prandom_u32_state(state);
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prandom_u32_state(state);
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prandom_u32_state(state);
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prandom_u32_state(state);
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prandom_u32_state(state);
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prandom_u32_state(state);
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prandom_u32_state(state);
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prandom_u32_state(state);
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prandom_u32_state(state);
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prandom_u32_state(state);
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}
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void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
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{
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int i;
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for_each_possible_cpu(i) {
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struct rnd_state *state = per_cpu_ptr(pcpu_state, i);
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u32 seeds[4];
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get_random_bytes(&seeds, sizeof(seeds));
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state->s1 = __seed(seeds[0], 2U);
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state->s2 = __seed(seeds[1], 8U);
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state->s3 = __seed(seeds[2], 16U);
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state->s4 = __seed(seeds[3], 128U);
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prandom_warmup(state);
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}
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}
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EXPORT_SYMBOL(prandom_seed_full_state);
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#ifdef CONFIG_RANDOM32_SELFTEST
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static struct prandom_test1 {
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u32 seed;
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u32 result;
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} test1[] = {
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{ 1U, 3484351685U },
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{ 2U, 2623130059U },
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{ 3U, 3125133893U },
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{ 4U, 984847254U },
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};
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static struct prandom_test2 {
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u32 seed;
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u32 iteration;
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u32 result;
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} test2[] = {
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/* Test cases against taus113 from GSL library. */
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{ 931557656U, 959U, 2975593782U },
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{ 1339693295U, 876U, 3887776532U },
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{ 1545556285U, 961U, 1615538833U },
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{ 601730776U, 723U, 1776162651U },
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{ 1027516047U, 687U, 511983079U },
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{ 416526298U, 700U, 916156552U },
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{ 1395522032U, 652U, 2222063676U },
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{ 366221443U, 617U, 2992857763U },
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{ 1539836965U, 714U, 3783265725U },
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{ 556206671U, 994U, 799626459U },
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{ 684907218U, 799U, 367789491U },
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{ 2121230701U, 931U, 2115467001U },
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{ 1668516451U, 644U, 3620590685U },
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{ 768046066U, 883U, 2034077390U },
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{ 1989159136U, 833U, 1195767305U },
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{ 536585145U, 996U, 3577259204U },
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{ 1008129373U, 642U, 1478080776U },
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{ 1740775604U, 939U, 1264980372U },
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{ 1967883163U, 508U, 10734624U },
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{ 1923019697U, 730U, 3821419629U },
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{ 442079932U, 560U, 3440032343U },
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{ 1961302714U, 845U, 841962572U },
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{ 2030205964U, 962U, 1325144227U },
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{ 1160407529U, 507U, 240940858U },
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{ 635482502U, 779U, 4200489746U },
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{ 1252788931U, 699U, 867195434U },
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{ 1961817131U, 719U, 668237657U },
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{ 1071468216U, 983U, 917876630U },
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{ 1281848367U, 932U, 1003100039U },
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{ 582537119U, 780U, 1127273778U },
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{ 1973672777U, 853U, 1071368872U },
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{ 1896756996U, 762U, 1127851055U },
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{ 847917054U, 500U, 1717499075U },
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{ 1240520510U, 951U, 2849576657U },
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{ 1685071682U, 567U, 1961810396U },
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{ 1516232129U, 557U, 3173877U },
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{ 1208118903U, 612U, 1613145022U },
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{ 1817269927U, 693U, 4279122573U },
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{ 1510091701U, 717U, 638191229U },
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{ 365916850U, 807U, 600424314U },
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{ 399324359U, 702U, 1803598116U },
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{ 1318480274U, 779U, 2074237022U },
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{ 697758115U, 840U, 1483639402U },
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{ 1696507773U, 840U, 577415447U },
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{ 2081979121U, 981U, 3041486449U },
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{ 955646687U, 742U, 3846494357U },
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{ 1250683506U, 749U, 836419859U },
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{ 595003102U, 534U, 366794109U },
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{ 47485338U, 558U, 3521120834U },
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{ 619433479U, 610U, 3991783875U },
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{ 704096520U, 518U, 4139493852U },
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{ 1712224984U, 606U, 2393312003U },
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{ 1318233152U, 922U, 3880361134U },
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{ 855572992U, 761U, 1472974787U },
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{ 64721421U, 703U, 683860550U },
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{ 678931758U, 840U, 380616043U },
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{ 692711973U, 778U, 1382361947U },
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{ 677703619U, 530U, 2826914161U },
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{ 92393223U, 586U, 1522128471U },
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{ 1222592920U, 743U, 3466726667U },
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{ 358288986U, 695U, 1091956998U },
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{ 1935056945U, 958U, 514864477U },
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{ 735675993U, 990U, 1294239989U },
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{ 1560089402U, 897U, 2238551287U },
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{ 70616361U, 829U, 22483098U },
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{ 368234700U, 731U, 2913875084U },
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{ 20221190U, 879U, 1564152970U },
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{ 539444654U, 682U, 1835141259U },
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{ 1314987297U, 840U, 1801114136U },
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{ 2019295544U, 645U, 3286438930U },
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{ 469023838U, 716U, 1637918202U },
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{ 1843754496U, 653U, 2562092152U },
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{ 400672036U, 809U, 4264212785U },
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{ 404722249U, 965U, 2704116999U },
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{ 600702209U, 758U, 584979986U },
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{ 519953954U, 667U, 2574436237U },
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{ 1658071126U, 694U, 2214569490U },
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{ 420480037U, 749U, 3430010866U },
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{ 690103647U, 969U, 3700758083U },
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{ 1029424799U, 937U, 3787746841U },
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{ 2012608669U, 506U, 3362628973U },
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{ 1535432887U, 998U, 42610943U },
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{ 1330635533U, 857U, 3040806504U },
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{ 1223800550U, 539U, 3954229517U },
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{ 1322411537U, 680U, 3223250324U },
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{ 1877847898U, 945U, 2915147143U },
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{ 1646356099U, 874U, 965988280U },
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{ 805687536U, 744U, 4032277920U },
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{ 1948093210U, 633U, 1346597684U },
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{ 392609744U, 783U, 1636083295U },
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{ 690241304U, 770U, 1201031298U },
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{ 1360302965U, 696U, 1665394461U },
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{ 1220090946U, 780U, 1316922812U },
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{ 447092251U, 500U, 3438743375U },
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{ 1613868791U, 592U, 828546883U },
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{ 523430951U, 548U, 2552392304U },
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{ 726692899U, 810U, 1656872867U },
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{ 1364340021U, 836U, 3710513486U },
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{ 1986257729U, 931U, 935013962U },
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{ 407983964U, 921U, 728767059U },
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};
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static void prandom_state_selftest_seed(struct rnd_state *state, u32 seed)
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{
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#define LCG(x) ((x) * 69069U) /* super-duper LCG */
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state->s1 = __seed(LCG(seed), 2U);
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state->s2 = __seed(LCG(state->s1), 8U);
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state->s3 = __seed(LCG(state->s2), 16U);
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state->s4 = __seed(LCG(state->s3), 128U);
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}
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static int __init prandom_state_selftest(void)
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{
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int i, j, errors = 0, runs = 0;
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bool error = false;
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for (i = 0; i < ARRAY_SIZE(test1); i++) {
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struct rnd_state state;
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prandom_state_selftest_seed(&state, test1[i].seed);
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prandom_warmup(&state);
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if (test1[i].result != prandom_u32_state(&state))
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error = true;
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}
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if (error)
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pr_warn("prandom: seed boundary self test failed\n");
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else
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pr_info("prandom: seed boundary self test passed\n");
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for (i = 0; i < ARRAY_SIZE(test2); i++) {
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struct rnd_state state;
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prandom_state_selftest_seed(&state, test2[i].seed);
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prandom_warmup(&state);
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for (j = 0; j < test2[i].iteration - 1; j++)
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prandom_u32_state(&state);
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if (test2[i].result != prandom_u32_state(&state))
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errors++;
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runs++;
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cond_resched();
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}
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if (errors)
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pr_warn("prandom: %d/%d self tests failed\n", errors, runs);
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else
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pr_info("prandom: %d self tests passed\n", runs);
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return 0;
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}
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core_initcall(prandom_state_selftest);
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#endif
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