xref: /openbsd/sys/arch/i386/stand/libsa/mdrandom.c (revision 54b0a309)

/*	$OpenBSD: mdrandom.c,v 1.4 2024/09/26 10:12:02 jsg Exp $	*/

/*
 * Copyright (c) 2020 Theo de Raadt
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/param.h>
#include <machine/specialreg.h>

#include "libsa.h"

int
mdrandom(char *buf, size_t buflen)
{
	u_int eax, ebx, ecx, edx;
	int ret = -1;
	int i;

	if (pslid() == 0)
		goto done;
	CPUID(1, eax, ebx, ecx, edx);
	if (edx & CPUID_TSC) {
		uint32_t hi, lo, acc;

		for (i = 0; i < buflen; i++) {
			__asm volatile("rdtsc" : "=d" (hi), "=a" (lo));
			acc = hi ^ lo;
			acc ^= acc >> 16;
			acc ^= acc >>  8;
			buf[i] ^= acc;
		}
		ret = 0;
	}
	if (ecx & CPUIDECX_RDRAND) {
		unsigned long rand;
		int retries;
		uint8_t valid;

		for (i = 0; i < buflen / sizeof(rand); i++) {
			retries = 10;
			do {
				__asm volatile(
				    "rdrand	%0;"
				    "setc	%1;"
				    : "=r" (rand), "=qm" (valid));
			} while (!valid && --retries > 0);
			((unsigned long *)buf)[i] ^= rand;
		}
		ret = 0;
	}
	CPUID(0, eax, ebx, ecx, edx);
	if (eax >= 7) {
		CPUID_LEAF(7, 0, eax, ebx, ecx, edx);
		if (ebx & SEFF0EBX_RDSEED) {
			unsigned long rand;
			int retries;
			uint8_t valid;

			for (i = 0; i < buflen / sizeof(rand); i++) {
				retries = 10;
				do {
					__asm volatile(
					    "rdseed	%0;"
					    "setc	%1;"
					    : "=r" (rand), "=qm" (valid));
				} while (!valid && --retries > 0);
				((unsigned long *)buf)[i] ^= rand;
			}
			ret = 0;
		}
	}
done:
	return ret;
}