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/* SPDX-License-Identifier: LGPL-2.1+ */
#if defined(__i386__) || defined(__x86_64__)
#include <cpuid.h>
#endif
#include <elf.h>
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>
#if HAVE_SYS_AUXV_H
# include <sys/auxv.h>
#endif
#if USE_SYS_RANDOM_H
# include <sys/random.h>
#else
# include <linux/random.h>
#endif
#include "alloc-util.h"
#include "fd-util.h"
#include "io-util.h"
#include "missing.h"
#include "random-util.h"
#include "time-util.h"
int rdrand(unsigned long *ret) {
#if defined(__i386__) || defined(__x86_64__)
static int have_rdrand = -1;
unsigned char err;
if (have_rdrand < 0) {
uint32_t eax, ebx, ecx, edx;
/* Check if RDRAND is supported by the CPU */
if (__get_cpuid(1, &eax, &ebx, &ecx, &edx) == 0) {
have_rdrand = false;
return -EOPNOTSUPP;
}
have_rdrand = !!(ecx & (1U << 30));
}
if (have_rdrand == 0)
return -EOPNOTSUPP;
asm volatile("rdrand %0;"
"setc %1"
: "=r" (*ret),
"=qm" (err));
msan_unpoison(&err, sizeof(err));
if (!err)
return -EAGAIN;
return 0;
#else
return -EOPNOTSUPP;
#endif
}
int genuine_random_bytes(void *p, size_t n, RandomFlags flags) {
static int have_syscall = -1;
_cleanup_close_ int fd = -1;
bool got_some = false;
int r;
/* Gathers some randomness from the kernel (or the CPU if the RANDOM_ALLOW_RDRAND flag is set). This call won't
* block, unless the RANDOM_BLOCK flag is set. If RANDOM_DONT_DRAIN is set, an error is returned if the random
* pool is not initialized. Otherwise it will always return some data from the kernel, regardless of whether
* the random pool is fully initialized or not. */
if (n == 0)
return 0;
if (FLAGS_SET(flags, RANDOM_ALLOW_RDRAND))
/* Try x86-64' RDRAND intrinsic if we have it. We only use it if high quality randomness is not
* required, as we don't trust it (who does?). Note that we only do a single iteration of RDRAND here,
* even though the Intel docs suggest calling this in a tight loop of 10 invocations or so. That's
* because we don't really care about the quality here. We generally prefer using RDRAND if the caller
* allows us too, since this way we won't drain the kernel randomness pool if we don't need it, as the
* pool's entropy is scarce. */
for (;;) {
unsigned long u;
size_t m;
if (rdrand(&u) < 0) {
if (got_some && FLAGS_SET(flags, RANDOM_EXTEND_WITH_PSEUDO)) {
/* Fill in the remaining bytes using pseudo-random values */
pseudo_random_bytes(p, n);
return 0;
}
/* OK, this didn't work, let's go to getrandom() + /dev/urandom instead */
break;
}
m = MIN(sizeof(u), n);
memcpy(p, &u, m);
p = (uint8_t*) p + m;
n -= m;
if (n == 0)
return 0; /* Yay, success! */
got_some = true;
}
/* Use the getrandom() syscall unless we know we don't have it. */
if (have_syscall != 0 && !HAS_FEATURE_MEMORY_SANITIZER) {
for (;;) {
r = getrandom(p, n, FLAGS_SET(flags, RANDOM_BLOCK) ? 0 : GRND_NONBLOCK);
if (r > 0) {
have_syscall = true;
if ((size_t) r == n)
return 0; /* Yay, success! */
assert((size_t) r < n);
p = (uint8_t*) p + r;
n -= r;
if (FLAGS_SET(flags, RANDOM_EXTEND_WITH_PSEUDO)) {
/* Fill in the remaining bytes using pseudo-random values */
pseudo_random_bytes(p, n);
return 0;
}
got_some = true;
/* Hmm, we didn't get enough good data but the caller insists on good data? Then try again */
if (FLAGS_SET(flags, RANDOM_BLOCK))
continue;
/* Fill in the rest with /dev/urandom */
break;
} else if (r == 0) {
have_syscall = true;
return -EIO;
} else if (errno == ENOSYS) {
/* We lack the syscall, continue with reading from /dev/urandom. */
have_syscall = false;
break;
} else if (errno == EAGAIN) {
/* The kernel has no entropy whatsoever. Let's remember to use the syscall the next
* time again though.
*
* If RANDOM_DONT_DRAIN is set, return an error so that random_bytes() can produce some
* pseudo-random bytes instead. Otherwise, fall back to /dev/urandom, which we know is empty,
* but the kernel will produce some bytes for us on a best-effort basis. */
have_syscall = true;
if (got_some && FLAGS_SET(flags, RANDOM_EXTEND_WITH_PSEUDO)) {
/* Fill in the remaining bytes using pseudorandom values */
pseudo_random_bytes(p, n);
return 0;
}
if (FLAGS_SET(flags, RANDOM_DONT_DRAIN))
return -ENODATA;
/* Use /dev/urandom instead */
break;
} else
return -errno;
}
}
fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY);
if (fd < 0)
return errno == ENOENT ? -ENOSYS : -errno;
return loop_read_exact(fd, p, n, true);
}
void initialize_srand(void) {
static bool srand_called = false;
unsigned x;
#if HAVE_SYS_AUXV_H
const void *auxv;
#endif
unsigned long k;
if (srand_called)
return;
#if HAVE_SYS_AUXV_H
/* The kernel provides us with 16 bytes of entropy in auxv, so let's
* try to make use of that to seed the pseudo-random generator. It's
* better than nothing... */
auxv = (const void*) getauxval(AT_RANDOM);
if (auxv) {
assert_cc(sizeof(x) <= 16);
memcpy(&x, auxv, sizeof(x));
} else
#endif
x = 0;
x ^= (unsigned) now(CLOCK_REALTIME);
x ^= (unsigned) gettid();
if (rdrand(&k) >= 0)
x ^= (unsigned) k;
srand(x);
srand_called = true;
}
/* INT_MAX gives us only 31 bits, so use 24 out of that. */
#if RAND_MAX >= INT_MAX
# define RAND_STEP 3
#else
/* SHORT_INT_MAX or lower gives at most 15 bits, we just just 8 out of that. */
# define RAND_STEP 1
#endif
void pseudo_random_bytes(void *p, size_t n) {
uint8_t *q;
initialize_srand();
for (q = p; q < (uint8_t*) p + n; q += RAND_STEP) {
unsigned rr;
rr = (unsigned) rand();
#if RAND_STEP >= 3
if ((size_t) (q - (uint8_t*) p + 2) < n)
q[2] = rr >> 16;
#endif
#if RAND_STEP >= 2
if ((size_t) (q - (uint8_t*) p + 1) < n)
q[1] = rr >> 8;
#endif
q[0] = rr;
}
}
void random_bytes(void *p, size_t n) {
if (genuine_random_bytes(p, n, RANDOM_EXTEND_WITH_PSEUDO|RANDOM_DONT_DRAIN|RANDOM_ALLOW_RDRAND) >= 0)
return;
/* If for some reason some user made /dev/urandom unavailable to us, or the kernel has no entropy, use a PRNG instead. */
pseudo_random_bytes(p, n);
}
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