/*      $NetBSD: prng.c,v 1.5 2021/05/04 21:13:38 khorben Exp $ */

/*
* Copyright (c) 2017-2020 The NetBSD Foundation, Inc. All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Maxime Villard.
*
* 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.
* 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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``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 FOUNDATION OR CONTRIBUTORS
* 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 "prekern.h"
#include <sys/sha1.h>
#include <sys/sha2.h>

#define _KERNEL
#include <machine/bootinfo.h>
#undef _KERNEL

#define CPUID_SEF_RDSEED        __BIT(18)
#define CPUID2_RDRAND   0x40000000
static bool has_rdrand = false;
static bool has_rdseed = false;

#define RND_SAVEWORDS   128
typedef struct {
       uint32_t entropy;
       uint8_t data[RND_SAVEWORDS * sizeof(uint32_t)];
       uint8_t digest[SHA1_DIGEST_LENGTH];
} rndsave_t;

#define RNGSTATE_SIZE   (SHA512_DIGEST_LENGTH / 2)
#define RNGDATA_SIZE    (SHA512_DIGEST_LENGTH / 2)
struct {
       uint8_t state[RNGSTATE_SIZE];
       uint8_t data[RNGDATA_SIZE];
       size_t nused;
} rng;

static struct btinfo_common *
prng_lookup_bootinfo(int type)
{
       extern struct bootinfo bootinfo;
       struct btinfo_common *bic;
       bool found;
       int i;

       bic = (struct btinfo_common *)(bootinfo.bi_data);
       found = false;
       for (i = 0; i < bootinfo.bi_nentries && !found; i++) {
               if (bic->type == type)
                       found = true;
               else
                       bic = (struct btinfo_common *)
                           ((uint8_t *)bic + bic->len);
       }
       return found ? bic : NULL;
}

static void
prng_get_entropy_file(SHA512_CTX *ctx)
{
       struct bi_modulelist_entry *bi, *bimax;
       struct btinfo_modulelist *biml;
       uint8_t digest[SHA1_DIGEST_LENGTH];
       rndsave_t *rndsave;
       SHA1_CTX sig;
       size_t count = 0;

       biml =
           (struct btinfo_modulelist *)prng_lookup_bootinfo(BTINFO_MODULELIST);
       if (biml == NULL) {
               return;
       }

       bi = (struct bi_modulelist_entry *)((uint8_t *)biml + sizeof(*biml));
       bimax = bi + biml->num;
       for (; bi < bimax; bi++) {
               if (bi->type != BI_MODULE_RND) {
                       continue;
               }
               if (bi->len != sizeof(rndsave_t)) {
                       print_state(STATE_WARNING,
                                       "size mismatch in entropy file");
                       continue;
               }
               rndsave = (rndsave_t *)(vaddr_t)bi->base;

               /* check the signature */
               SHA1Init(&sig);
               SHA1Update(&sig, (uint8_t *)&rndsave->entropy,
                   sizeof(rndsave->entropy));
               SHA1Update(&sig, rndsave->data, sizeof(rndsave->data));
               SHA1Final(digest, &sig);
               if (memcmp(digest, rndsave->digest, sizeof(digest))) {
                       print_state(STATE_WARNING,
                                       "bad SHA1 checksum in entropy file");
                       continue;
               }

               SHA512_Update(ctx, rndsave->data, sizeof(rndsave->data));
               count++;
       }
       if (count == 0)
               print_state(STATE_WARNING, "No entropy file could be loaded");
}

/*
* Add 32 bytes of rdseed/rdrand and 8 bytes of rdtsc to the context.
*/
static void
prng_get_entropy_data(SHA512_CTX *ctx)
{
       uint64_t buf[8], val;
       size_t i;

       if (has_rdseed) {
               for (i = 0; i < 8; i++) {
                       if (rdseed(&buf[i]) == -1) {
                               break;
                       }
               }
               SHA512_Update(ctx, (uint8_t *)buf, i * sizeof(uint64_t));
       } else if (has_rdrand) {
               for (i = 0; i < 8; i++) {
                       if (rdrand(&buf[i]) == -1) {
                               break;
                       }
               }
               SHA512_Update(ctx, (uint8_t *)buf, i * sizeof(uint64_t));
       }

       val = rdtsc();
       SHA512_Update(ctx, (uint8_t *)&val, sizeof(val));
}

void
prng_init(void)
{
       extern int cpuid_level;
       uint8_t digest[SHA512_DIGEST_LENGTH];
       SHA512_CTX ctx;
       u_int descs[4];

       memset(&rng, 0, sizeof(rng));

       /* detect cpu features */
       if (cpuid_level >= 0x07) {
               cpuid(0x07, 0x00, descs);
               has_rdseed = (descs[1] & CPUID_SEF_RDSEED) != 0;
       }
       if (cpuid_level >= 0x01) {
               cpuid(0x01, 0x00, descs);
               has_rdrand = (descs[2] & CPUID2_RDRAND) != 0;
       }
       if (!has_rdseed && !has_rdrand)
               print_state(STATE_WARNING, "No CPU entropy feature detected");

       SHA512_Init(&ctx);
       prng_get_entropy_file(&ctx);
       prng_get_entropy_data(&ctx);
       SHA512_Final(digest, &ctx);

       memcpy(rng.state, digest, RNGSTATE_SIZE);
       memcpy(rng.data, digest + RNGSTATE_SIZE, RNGDATA_SIZE);
}

static void
prng_round(void)
{
       uint8_t digest[SHA512_DIGEST_LENGTH];
       SHA512_CTX ctx;

       SHA512_Init(&ctx);
       SHA512_Update(&ctx, rng.state, RNGSTATE_SIZE);
       prng_get_entropy_data(&ctx);
       SHA512_Final(digest, &ctx);

       memcpy(rng.state, digest, RNGSTATE_SIZE);
       memcpy(rng.data, digest + RNGSTATE_SIZE, RNGDATA_SIZE);

       rng.nused = 0;
}

void
prng_get_rand(void *buf, size_t sz)
{
       uint8_t *ptr = (uint8_t *)buf;
       size_t consumed;

       ASSERT(sz <= RNGDATA_SIZE);
       if (rng.nused + sz > RNGDATA_SIZE) {
               /* Fill what can be */
               consumed = RNGDATA_SIZE - rng.nused;
               memcpy(ptr, &rng.data[rng.nused], consumed);

               /* Go through another round */
               prng_round();

               /* Fill the rest */
               memcpy(ptr + consumed, &rng.data[rng.nused],
                   sz - consumed);

               rng.nused += (sz - consumed);
       } else {
               memcpy(ptr, &rng.data[rng.nused], sz);
               rng.nused += sz;
       }
}

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