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https://github.com/morgan9e/systemd
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ffa047a03e
/dev/urandom is seeded with RDRAND. Calling genuine_random_bytes(..., ..., 0) will use /dev/urandom as a last resort. Hence, we gain nothing here by having our own RDRAND wrapper, because /dev/urandom already is based on RDRAND output, even before /dev/urandom has fully initialized. Furthermore, RDRAND is not actually fast! And on each successive generation of new x86 CPUs, from both AMD and Intel, it just gets slower. This commit simplifies things by just using /dev/urandom in cases where we before might use RDRAND, since /dev/urandom will always have RDRAND mixed in as part of it. And above where I say "/dev/urandom", what I actually mean is GRND_INSECURE, which is the same thing but won't generate warnings in dmesg.
39 lines
1.3 KiB
C
39 lines
1.3 KiB
C
/* SPDX-License-Identifier: LGPL-2.1-or-later */
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#pragma once
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#include <stdbool.h>
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#include <stddef.h>
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#include <stdint.h>
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typedef enum RandomFlags {
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RANDOM_BLOCK = 1 << 0, /* Rather block than return crap randomness (only if the kernel supports that) */
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} RandomFlags;
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int genuine_random_bytes(void *p, size_t n, RandomFlags flags); /* returns "genuine" randomness, optionally filled up with pseudo random, if not enough is available */
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void pseudo_random_bytes(void *p, size_t n); /* returns only pseudo-randommess (but possibly seeded from something better) */
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void random_bytes(void *p, size_t n); /* returns genuine randomness if cheaply available, and pseudo randomness if not. */
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void initialize_srand(void);
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static inline uint64_t random_u64(void) {
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uint64_t u;
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random_bytes(&u, sizeof(u));
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return u;
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}
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static inline uint32_t random_u32(void) {
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uint32_t u;
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random_bytes(&u, sizeof(u));
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return u;
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}
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/* Some limits on the pool sizes when we deal with the kernel random pool */
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#define RANDOM_POOL_SIZE_MIN 512U
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#define RANDOM_POOL_SIZE_MAX (10U*1024U*1024U)
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size_t random_pool_size(void);
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int random_write_entropy(int fd, const void *seed, size_t size, bool credit);
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uint64_t random_u64_range(uint64_t max);
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