/*-
 * Copyright (c) 2013, 2025, David E. O'Brien <deo@NUXI.org>
 * Copyright (c) 2013 The FreeBSD Foundation
 * Copyright (c) 2012 Konstantin Belousov <kib@FreeBSD.org>
 * All rights reserved.
 *
 * Portions of this software were developed by Konstantin Belousov
 * under sponsorship from the FreeBSD Foundation.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer
 *    in this position and unchanged.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/conf.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/random.h>
#include <sys/sysctl.h>
#include <sys/systm.h>

#include <machine/md_var.h>
#include <machine/specialreg.h>
#include <x86/ifunc.h>

#include <dev/random/randomdev.h>

#define RETRY_COUNT     10

static u_int random_ivy_read(void *, u_int);

static const struct random_source random_ivy = {
        .rs_ident = "Intel Secure Key RNG",
        .rs_source = RANDOM_PURE_RDRAND,
        .rs_read = random_ivy_read
};

static bool acquire_independent_seed_samples = false;

static bool
x86_rdrand_store(u_long *buf)
{
        u_long rndval, seed_iterations, i;
        int retry;

        /* Per [1], "§ 5.2.6 Generating Seeds from RDRAND,"
         * machines lacking RDSEED will guarantee RDRAND is reseeded every 8kB
         * of generated output.
         *
         * [1]: https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide#inpage-nav-6-8
         */
        if (acquire_independent_seed_samples)
                seed_iterations = 8 * 1024 / sizeof(*buf);
        else
                seed_iterations = 1;

        for (i = 0; i < seed_iterations; i++) {
                retry = RETRY_COUNT;
                __asm __volatile(
                    "1:\n\t"
                    "rdrand     %1\n\t" /* read randomness into rndval */
                    "jc         2f\n\t" /* CF is set on success, exit retry loop */
                    "dec        %0\n\t" /* otherwise, retry-- */
                    "jne        1b\n\t" /* and loop if retries are not exhausted */
                    "2:"
                    : "+r" (retry), "=r" (rndval) : : "cc");
                if (retry == 0)
                        return (false);
        }
        *buf = rndval;
        return (true);
}

/* It is required that buf length is a multiple of sizeof(u_long). */
static u_int
random_ivy_read(void *buf, u_int c)
{
        u_long *b, rndval;
        u_int count;

        KASSERT(c % sizeof(*b) == 0, ("partial read %d", c));
        b = buf;
        for (count = c; count > 0; count -= sizeof(*b)) {
                if (!x86_rdrand_store(&rndval))
                        break;
                *b++ = rndval;
        }
        return (c - count);
}

static int
rdrand_modevent(module_t mod, int type, void *unused)
{
        struct sysctl_ctx_list ctx;
        struct sysctl_oid *o;
        bool has_rdrand, has_rdseed;
        int error = 0;

        has_rdrand = (cpu_feature2 & CPUID2_RDRAND);
        has_rdseed = (cpu_stdext_feature & CPUID_STDEXT_RDSEED);

        switch (type) {
        case MOD_LOAD:
                if (has_rdrand && !has_rdseed) {
                        sysctl_ctx_init(&ctx);
                        o = SYSCTL_ADD_NODE(&ctx, SYSCTL_STATIC_CHILDREN(_kern_random),
                            OID_AUTO, "rdrand", CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
                            "rdrand (ivy) entropy source");
                        SYSCTL_ADD_BOOL(&ctx, SYSCTL_CHILDREN(o), OID_AUTO,
                            "rdrand_independent_seed", CTLFLAG_RDTUN,
                            &acquire_independent_seed_samples, 0,
        "If non-zero, use more expensive and slow, but safer, seeded samples "
        "where RDSEED is not present.");
                        random_source_register(&random_ivy);
                        printf("random: fast provider: \"%s\"\n", random_ivy.rs_ident);
                }
                break;

        case MOD_UNLOAD:
                if (has_rdrand && !has_rdseed)
                        random_source_deregister(&random_ivy);
                break;

        case MOD_SHUTDOWN:
                break;

        default:
                error = EOPNOTSUPP;
                break;

        }

        return (error);
}

static moduledata_t rdrand_mod = {
        "rdrand",
        rdrand_modevent,
        0
};

DECLARE_MODULE(rdrand, rdrand_mod, SI_SUB_RANDOM, SI_ORDER_FOURTH);
MODULE_VERSION(rdrand, 1);
MODULE_DEPEND(rdrand, random_harvestq, 1, 1, 1);