/*      $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;
}