112 lines
3.0 KiB
C
112 lines
3.0 KiB
C
// Copyright 2013-2022 Nicholas J. Kain <njkain at gmail dot com>
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// SPDX-License-Identifier: MIT
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#include <stdint.h>
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#include <string.h>
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#include <stdbool.h>
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#include <unistd.h>
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#include <errno.h>
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#include <time.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include "nk/hwrng.h"
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#include "nk/log.h"
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#include "nk/io.h"
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#ifdef NK_NO_GETRANDOM_SYSCALL
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static bool nk_getrandom(char *seed, size_t len)
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{
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(void)seed;
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(void)len;
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return false;
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}
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#else
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#ifdef NK_NO_GETRANDOM_LIBC
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#include <sys/syscall.h>
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#include <linux/random.h>
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#define NK_GETRANDOM_CALL(A,B,C) syscall(SYS_getrandom, (A), (B), (C))
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#else
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#include <sys/random.h>
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#define NK_GETRANDOM_CALL(A,B,C) getrandom((A), (B), (C))
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#endif
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static bool nk_getrandom(char *seed, size_t len)
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{
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size_t fetched = 0;
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while (fetched < len) {
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int r = NK_GETRANDOM_CALL(seed + fetched, len - fetched, 0);
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if (r <= 0) {
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if (r == 0) {
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// Failsafe to guard against infinite loops.
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log_line("%s: getrandom() returned no entropy", __func__);
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return false;
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}
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if (errno == EINTR) continue;
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if (errno == ENOSYS) return false; // Kernel doesn't support syscall
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log_line("%s: getrandom() failed: %s", __func__, strerror(errno));
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return false;
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}
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fetched += (size_t)r;
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}
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return true;
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}
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#endif
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#undef NK_GETRANDOM_CALL
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static bool nk_get_rnd_clk(char *seed, size_t len)
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{
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struct timespec ts;
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for (size_t i = 0; i < len; ++i) {
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int r = clock_gettime(CLOCK_REALTIME, &ts);
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if (r < 0) {
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log_line("%s: Could not call clock_gettime(CLOCK_REALTIME): %s",
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__func__, strerror(errno));
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return false;
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}
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char *p = (char *)&ts.tv_sec;
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char *q = (char *)&ts.tv_nsec;
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for (size_t j = 0; j < sizeof ts.tv_sec; ++j)
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seed[i] ^= p[j];
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for (size_t j = 0; j < sizeof ts.tv_nsec; ++j)
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seed[i] ^= q[j];
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// Force some scheduler jitter.
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static const struct timespec st = { .tv_sec=0, .tv_nsec=1 };
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nanosleep(&st, (struct timespec *)0);
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}
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return true;
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}
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static bool nk_get_urandom(char *seed, size_t len)
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{
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int fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC);
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if (fd < 0) {
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log_line("%s: Could not open /dev/urandom: %s", __func__,
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strerror(errno));
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return false;
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}
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bool ret = true;
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int r = safe_read(fd, seed, len);
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if (r < 0) {
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ret = false;
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log_line("%s: Could not read /dev/urandom: %s",
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__func__, strerror(errno));
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}
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close(fd);
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return ret;
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}
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void nk_get_hwrng(void *seed, size_t len)
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{
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char *s = (char *)seed;
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if (nk_getrandom(s, len))
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return;
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if (nk_get_urandom(s, len))
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return;
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log_line("%s: Seeding PRNG via system clock. May be predictable.",
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__func__);
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if (nk_get_rnd_clk(s, len))
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return;
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suicide("%s: All methods to seed PRNG failed. Exiting.", __func__);
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}
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