/*
 * Copyright (c) 2014 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Alex Hornung <alex@alexhornung.com>
 *
 * 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.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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
 * COPYRIGHT HOLDERS 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 <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/spinlock.h>
#include <sys/spinlock2.h>
#include <sys/csprng.h>

#define CHACHA_EMBED
#define CHACHA_NONCE0_CTR128
#define KEYSTREAM_ONLY
#include <crypto/chacha20/chacha.c>
#include <crypto/sha2/sha2.h>

/*
 * Minimum amount of bytes in pool before we consider it
 * good enough.
 * It's 64 + the hash digest size because we always
 * reinitialize the pools with a hash of the previous chunk
 * of entropy.
 */
#define MIN_POOL_SIZE   (64 + SHA256_DIGEST_LENGTH)

/* Minimum reseed interval */
#define MIN_RESEED_INTERVAL     hz/10

#if 0
static void csprng_reseed_callout(void *arg);
#endif
static int csprng_reseed(struct csprng_state *state);

static struct timeval csprng_reseed_interval = { 0, 100000 };

static
int
csprng_pool_init(struct csprng_pool *pool, uint8_t *buf, size_t len)
{
        pool->bytes = 0;
        SHA256_Init(&pool->hash_ctx);

        if (len > 0)
                SHA256_Update(&pool->hash_ctx, buf, len);

        return 0;
}

int
csprng_init(struct csprng_state *state)
{
        int i, r;

        bzero(state->key, sizeof(state->key));
        bzero(&state->cipher_ctx, sizeof(state->cipher_ctx));
        bzero(state->src_pool_idx, sizeof(state->src_pool_idx));
        bzero(&state->last_reseed, sizeof(state->last_reseed));

        state->reseed_cnt = 0;
        state->failed_reseeds = 0;
        state->callout_based_reseed = 0;

        for (i = 0; i < 32; i++) {
                r = csprng_pool_init(&state->pool[i], NULL, 0);
                if (r != 0)
                        break;
        }

        return r;
}

#if 0
int
csprng_init_reseed(struct csprng_state *state)
{
        state->callout_based_reseed = 1;

        callout_init_mp(&state->reseed_callout);
        callout_reset(&state->reseed_callout, MIN_RESEED_INTERVAL,
                      csprng_reseed_callout, state);

        return 0;
}
#endif

/*
 * XXX:
 * Sources don't really a uniquely-allocated src id...
 * another way we could do that is by simply using
 * (uint8_t)__LINE__ as the source id... cheap & cheerful.
 */

/*
 * Called with state->spin held.
 */
int
csprng_get_random(struct csprng_state *state, uint8_t *out, int bytes,
                  int flags)
{
        int cnt;
        int total_bytes = 0;

again:
        if (!state->callout_based_reseed &&
             ratecheck(&state->last_reseed, &csprng_reseed_interval)) {
                csprng_reseed(state);
        }

        /*
         * If no reseed has occurred yet, we can't possibly give out
         * any random data.
         * If this isn't an unlimited (i.e., /dev/urandom) read, sleep
         * until entropy is added to the pools (or a callout-based
         * reseed, if enabled, occurs).
         */
        if ((flags & CSPRNG_UNLIMITED) == 0 && state->reseed_cnt == 0) {
                ssleep(state, &state->spin, 0, "csprngrsd", 0);
                goto again;
        }

        while (bytes > 0) {
                /* Limit amount of output without rekeying to 2^20 */
                cnt = (bytes > (1 << 20)) ? (1 << 20) : bytes;

                chacha_encrypt_bytes(&state->cipher_ctx, NULL, out, cnt);

                /* Update key and rekey cipher */
                chacha_encrypt_bytes(&state->cipher_ctx, NULL, state->key,
                                     sizeof(state->key));
                chacha_keysetup(&state->cipher_ctx, state->key,
                                8 * sizeof(state->key));

                out += cnt;
                bytes -= cnt;
                total_bytes += cnt;
        }

        return total_bytes;
}

/*
 * Called with state->spin held.
 */
static
int
csprng_reseed(struct csprng_state *state)
{
        int i;
        struct csprng_pool *pool;
        SHA256_CTX hash_ctx;
        uint8_t digest[SHA256_DIGEST_LENGTH];
        uint8_t counter[16];

        /*
         * If there's not enough entropy in the first
         * pool, don't reseed.
         */
        if (state->pool[0].bytes < MIN_POOL_SIZE) {
                ++state->failed_reseeds;
                return 1;
        }

        SHA256_Init(&hash_ctx);

        /*
         * Update hash that will result in new key with the
         * old key.
         */
        SHA256_Update(&hash_ctx, state->key, sizeof(state->key));

        state->reseed_cnt++;

        for (i = 0; i < 32; i++) {
                if ((state->reseed_cnt % (1 << i)) != 0)
                        break;

                pool = &state->pool[i];

                /*
                 * Finalize hash of the entropy in this pool.
                 */
                SHA256_Final(digest, &pool->hash_ctx);

                /*
                 * Reinitialize pool with a hash of the old pool digest.
                 * This is a slight deviation from Fortuna as per reference,
                 * but is in line with other Fortuna implementations.
                 */
                csprng_pool_init(pool, digest, sizeof(digest));

                /*
                 * Update hash that will result in new key with this
                 * pool's hashed entropy.
                 */
                SHA256_Update(&hash_ctx, digest, sizeof(digest));
        }

        SHA256_Final(state->key, &hash_ctx);

        /* Update key and rekey cipher */
        chacha_keysetup(&state->cipher_ctx, state->key, 8*sizeof(state->key));

        /* No IV but a 128-bit counter, should never overflow */
        bzero(counter, sizeof(counter));
        chacha_ivsetup(&state->cipher_ctx, NULL, counter);

        return 0;
}

#if 0
static
void
csprng_reseed_callout(void *arg)
{
        struct csprng_state *state = (struct csprng_state *)arg;
        int reseed_interval = MIN_RESEED_INTERVAL;

        spin_lock(&state->spin);
        csprng_reseed(arg);
        spin_unlock(&state->spin);
        wakeup(state);

        callout_reset(&state->reseed_callout, reseed_interval,
                      csprng_reseed_callout, state);
}
#endif

/*
 * Called with state->spin held
 */
int
csprng_add_entropy(struct csprng_state *state, int src_id,
                   const uint8_t *entropy, size_t bytes, int flags)
{
        struct csprng_pool *pool;
        int pool_id;

        /*
         * Pick the next pool for this source on a round-robin
         * basis.
         */
        src_id &= 0xff;
        pool_id = state->src_pool_idx[src_id]++ & 0x1f;
        pool = &state->pool[pool_id];

        SHA256_Update(&pool->hash_ctx, (const uint8_t *)&src_id,
                      sizeof(src_id));
        SHA256_Update(&pool->hash_ctx, (const uint8_t *)&bytes,
                      sizeof(bytes));
        SHA256_Update(&pool->hash_ctx, entropy, bytes);

        pool->bytes += bytes;

        return 0;
}