1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3 * include/linux/prandom.h
4 *
5 * Include file for the fast pseudo-random 32-bit
6 * generation.
7 */
8 #ifndef _LINUX_PRANDOM_H
9 #define _LINUX_PRANDOM_H
10
11 #include <linux/types.h>
12 #include <linux/percpu.h>
13
14 u32 prandom_u32(void);
15 void prandom_bytes(void *buf, size_t nbytes);
16 void prandom_seed(u32 seed);
17 void prandom_reseed_late(void);
18
19 #if BITS_PER_LONG == 64
20 /*
21 * The core SipHash round function. Each line can be executed in
22 * parallel given enough CPU resources.
23 */
24 #define PRND_SIPROUND(v0, v1, v2, v3) ( \
25 v0 += v1, v1 = rol64(v1, 13), v2 += v3, v3 = rol64(v3, 16), \
26 v1 ^= v0, v0 = rol64(v0, 32), v3 ^= v2, \
27 v0 += v3, v3 = rol64(v3, 21), v2 += v1, v1 = rol64(v1, 17), \
28 v3 ^= v0, v1 ^= v2, v2 = rol64(v2, 32) \
29 )
30
31 #define PRND_K0 (0x736f6d6570736575 ^ 0x6c7967656e657261)
32 #define PRND_K1 (0x646f72616e646f6d ^ 0x7465646279746573)
33
34 #elif BITS_PER_LONG == 32
35 /*
36 * On 32-bit machines, we use HSipHash, a reduced-width version of SipHash.
37 * This is weaker, but 32-bit machines are not used for high-traffic
38 * applications, so there is less output for an attacker to analyze.
39 */
40 #define PRND_SIPROUND(v0, v1, v2, v3) ( \
41 v0 += v1, v1 = rol32(v1, 5), v2 += v3, v3 = rol32(v3, 8), \
42 v1 ^= v0, v0 = rol32(v0, 16), v3 ^= v2, \
43 v0 += v3, v3 = rol32(v3, 7), v2 += v1, v1 = rol32(v1, 13), \
44 v3 ^= v0, v1 ^= v2, v2 = rol32(v2, 16) \
45 )
46 #define PRND_K0 0x6c796765
47 #define PRND_K1 0x74656462
48
49 #else
50 #error Unsupported BITS_PER_LONG
51 #endif
52
53 struct rnd_state {
54 __u32 s1, s2, s3, s4;
55 };
56
57 u32 prandom_u32_state(struct rnd_state *state);
58 void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
59 void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state);
60
61 #define prandom_init_once(pcpu_state) \
62 DO_ONCE(prandom_seed_full_state, (pcpu_state))
63
64 /**
65 * prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro)
66 * @ep_ro: right open interval endpoint
67 *
68 * Returns a pseudo-random number that is in interval [0, ep_ro). Note
69 * that the result depends on PRNG being well distributed in [0, ~0U]
70 * u32 space. Here we use maximally equidistributed combined Tausworthe
71 * generator, that is, prandom_u32(). This is useful when requesting a
72 * random index of an array containing ep_ro elements, for example.
73 *
74 * Returns: pseudo-random number in interval [0, ep_ro)
75 */
prandom_u32_max(u32 ep_ro)76 static inline u32 prandom_u32_max(u32 ep_ro)
77 {
78 return (u32)(((u64) prandom_u32() * ep_ro) >> 32);
79 }
80
81 /*
82 * Handle minimum values for seeds
83 */
__seed(u32 x,u32 m)84 static inline u32 __seed(u32 x, u32 m)
85 {
86 return (x < m) ? x + m : x;
87 }
88
89 /**
90 * prandom_seed_state - set seed for prandom_u32_state().
91 * @state: pointer to state structure to receive the seed.
92 * @seed: arbitrary 64-bit value to use as a seed.
93 */
prandom_seed_state(struct rnd_state * state,u64 seed)94 static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
95 {
96 u32 i = ((seed >> 32) ^ (seed << 10) ^ seed) & 0xffffffffUL;
97
98 state->s1 = __seed(i, 2U);
99 state->s2 = __seed(i, 8U);
100 state->s3 = __seed(i, 16U);
101 state->s4 = __seed(i, 128U);
102 }
103
104 /* Pseudo random number generator from numerical recipes. */
next_pseudo_random32(u32 seed)105 static inline u32 next_pseudo_random32(u32 seed)
106 {
107 return seed * 1664525 + 1013904223;
108 }
109
110 #endif
111