/* LRW: as defined by Cyril Guyot in
 *      http://grouper.ieee.org/groups/1619/email/pdf00017.pdf
 *
 * Copyright (c) 2006 Rik Snel <rsnel@cube.dyndns.org>
 *
 * Based on ecb.c
 * Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 */
/* This implementation is checked against the test vectors in the above
 * document and by a test vector provided by Ken Buchanan at
 * http://www.mail-archive.com/stds-p1619@listserv.ieee.org/msg00173.html
 *
 * The test vectors are included in the testing module tcrypt.[ch] */

#include <crypto/internal/skcipher.h>
#include <crypto/scatterwalk.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/scatterlist.h>
#include <linux/slab.h>

#include <crypto/b128ops.h>
#include <crypto/gf128mul.h>

#define LRW_BLOCK_SIZE 16

struct priv {
        struct crypto_skcipher *child;

        /*
         * optimizes multiplying a random (non incrementing, as at the
         * start of a new sector) value with key2, we could also have
         * used 4k optimization tables or no optimization at all. In the
         * latter case we would have to store key2 here
         */
        struct gf128mul_64k *table;

        /*
         * stores:
         *  key2*{ 0,0,...0,0,0,0,1 }, key2*{ 0,0,...0,0,0,1,1 },
         *  key2*{ 0,0,...0,0,1,1,1 }, key2*{ 0,0,...0,1,1,1,1 }
         *  key2*{ 0,0,...1,1,1,1,1 }, etc
         * needed for optimized multiplication of incrementing values
         * with key2
         */
        be128 mulinc[128];
};

struct rctx {
        be128 t;
        struct skcipher_request subreq;
};

static inline void setbit128_bbe(void *b, int bit)
{
        __set_bit(bit ^ (0x80 -
#ifdef __BIG_ENDIAN
                         BITS_PER_LONG
#else
                         BITS_PER_BYTE
#endif
                        ), b);
}

static int setkey(struct crypto_skcipher *parent, const u8 *key,
                  unsigned int keylen)
{
        struct priv *ctx = crypto_skcipher_ctx(parent);
        struct crypto_skcipher *child = ctx->child;
        int err, bsize = LRW_BLOCK_SIZE;
        const u8 *tweak = key + keylen - bsize;
        be128 tmp = { 0 };
        int i;

        crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
        crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
                                         CRYPTO_TFM_REQ_MASK);
        err = crypto_skcipher_setkey(child, key, keylen - bsize);
        crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) &
                                          CRYPTO_TFM_RES_MASK);
        if (err)
                return err;

        if (ctx->table)
                gf128mul_free_64k(ctx->table);

        /* initialize multiplication table for Key2 */
        ctx->table = gf128mul_init_64k_bbe((be128 *)tweak);
        if (!ctx->table)
                return -ENOMEM;

        /* initialize optimization table */
        for (i = 0; i < 128; i++) {
                setbit128_bbe(&tmp, i);
                ctx->mulinc[i] = tmp;
                gf128mul_64k_bbe(&ctx->mulinc[i], ctx->table);
        }

        return 0;
}

/*
 * Returns the number of trailing '1' bits in the words of the counter, which is
 * represented by 4 32-bit words, arranged from least to most significant.
 * At the same time, increments the counter by one.
 *
 * For example:
 *
 * u32 counter[4] = { 0xFFFFFFFF, 0x1, 0x0, 0x0 };
 * int i = next_index(&counter);
 * // i == 33, counter == { 0x0, 0x2, 0x0, 0x0 }
 */
static int next_index(u32 *counter)
{
        int i, res = 0;

        for (i = 0; i < 4; i++) {
                if (counter[i] + 1 != 0)
                        return res + ffz(counter[i]++);

                counter[i] = 0;
                res += 32;
        }

        /*
         * If we get here, then x == 128 and we are incrementing the counter
         * from all ones to all zeros. This means we must return index 127, i.e.
         * the one corresponding to key2*{ 1,...,1 }.
         */
        return 127;
}

/*
 * We compute the tweak masks twice (both before and after the ECB encryption or
 * decryption) to avoid having to allocate a temporary buffer and/or make
 * mutliple calls to the 'ecb(..)' instance, which usually would be slower than
 * just doing the next_index() calls again.
 */
static int xor_tweak(struct skcipher_request *req, bool second_pass)
{
        const int bs = LRW_BLOCK_SIZE;
        struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
        struct priv *ctx = crypto_skcipher_ctx(tfm);
        struct rctx *rctx = skcipher_request_ctx(req);
        be128 t = rctx->t;
        struct skcipher_walk w;
        __be32 *iv;
        u32 counter[4];
        int err;

        if (second_pass) {
                req = &rctx->subreq;
                /* set to our TFM to enforce correct alignment: */
                skcipher_request_set_tfm(req, tfm);
        }

        err = skcipher_walk_virt(&w, req, false);
        iv = (__be32 *)w.iv;

        counter[0] = be32_to_cpu(iv[3]);
        counter[1] = be32_to_cpu(iv[2]);
        counter[2] = be32_to_cpu(iv[1]);
        counter[3] = be32_to_cpu(iv[0]);

        while (w.nbytes) {
                unsigned int avail = w.nbytes;
                be128 *wsrc;
                be128 *wdst;

                wsrc = w.src.virt.addr;
                wdst = w.dst.virt.addr;

                do {
                        be128_xor(wdst++, &t, wsrc++);

                        /* T <- I*Key2, using the optimization
                         * discussed in the specification */
                        be128_xor(&t, &t, &ctx->mulinc[next_index(counter)]);
                } while ((avail -= bs) >= bs);

                if (second_pass && w.nbytes == w.total) {
                        iv[0] = cpu_to_be32(counter[3]);
                        iv[1] = cpu_to_be32(counter[2]);
                        iv[2] = cpu_to_be32(counter[1]);
                        iv[3] = cpu_to_be32(counter[0]);
                }

                err = skcipher_walk_done(&w, avail);
        }

        return err;
}

static int xor_tweak_pre(struct skcipher_request *req)
{
        return xor_tweak(req, false);
}

static int xor_tweak_post(struct skcipher_request *req)
{
        return xor_tweak(req, true);
}

static void crypt_done(struct crypto_async_request *areq, int err)
{
        struct skcipher_request *req = areq->data;

        if (!err) {
                struct rctx *rctx = skcipher_request_ctx(req);

                rctx->subreq.base.flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
                err = xor_tweak_post(req);
        }

        skcipher_request_complete(req, err);
}

static void init_crypt(struct skcipher_request *req)
{
        struct priv *ctx = crypto_skcipher_ctx(crypto_skcipher_reqtfm(req));
        struct rctx *rctx = skcipher_request_ctx(req);
        struct skcipher_request *subreq = &rctx->subreq;

        skcipher_request_set_tfm(subreq, ctx->child);
        skcipher_request_set_callback(subreq, req->base.flags, crypt_done, req);
        /* pass req->iv as IV (will be used by xor_tweak, ECB will ignore it) */
        skcipher_request_set_crypt(subreq, req->dst, req->dst,
                                   req->cryptlen, req->iv);

        /* calculate first value of T */
        memcpy(&rctx->t, req->iv, sizeof(rctx->t));

        /* T <- I*Key2 */
        gf128mul_64k_bbe(&rctx->t, ctx->table);
}

static int encrypt(struct skcipher_request *req)
{
        struct rctx *rctx = skcipher_request_ctx(req);
        struct skcipher_request *subreq = &rctx->subreq;

        init_crypt(req);
        return xor_tweak_pre(req) ?:
                crypto_skcipher_encrypt(subreq) ?:
                xor_tweak_post(req);
}

static int decrypt(struct skcipher_request *req)
{
        struct rctx *rctx = skcipher_request_ctx(req);
        struct skcipher_request *subreq = &rctx->subreq;

        init_crypt(req);
        return xor_tweak_pre(req) ?:
                crypto_skcipher_decrypt(subreq) ?:
                xor_tweak_post(req);
}

static int init_tfm(struct crypto_skcipher *tfm)
{
        struct skcipher_instance *inst = skcipher_alg_instance(tfm);
        struct crypto_skcipher_spawn *spawn = skcipher_instance_ctx(inst);
        struct priv *ctx = crypto_skcipher_ctx(tfm);
        struct crypto_skcipher *cipher;

        cipher = crypto_spawn_skcipher(spawn);
        if (IS_ERR(cipher))
                return PTR_ERR(cipher);

        ctx->child = cipher;

        crypto_skcipher_set_reqsize(tfm, crypto_skcipher_reqsize(cipher) +
                                         sizeof(struct rctx));

        return 0;
}

static void exit_tfm(struct crypto_skcipher *tfm)
{
        struct priv *ctx = crypto_skcipher_ctx(tfm);

        if (ctx->table)
                gf128mul_free_64k(ctx->table);
        crypto_free_skcipher(ctx->child);
}

static void free(struct skcipher_instance *inst)
{
        crypto_drop_skcipher(skcipher_instance_ctx(inst));
        kfree(inst);
}

static int create(struct crypto_template *tmpl, struct rtattr **tb)
{
        struct crypto_skcipher_spawn *spawn;
        struct skcipher_instance *inst;
        struct crypto_attr_type *algt;
        struct skcipher_alg *alg;
        const char *cipher_name;
        char ecb_name[CRYPTO_MAX_ALG_NAME];
        int err;

        algt = crypto_get_attr_type(tb);
        if (IS_ERR(algt))
                return PTR_ERR(algt);

        if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
                return -EINVAL;

        cipher_name = crypto_attr_alg_name(tb[1]);
        if (IS_ERR(cipher_name))
                return PTR_ERR(cipher_name);

        inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
        if (!inst)
                return -ENOMEM;

        spawn = skcipher_instance_ctx(inst);

        crypto_set_skcipher_spawn(spawn, skcipher_crypto_instance(inst));
        err = crypto_grab_skcipher(spawn, cipher_name, 0,
                                   crypto_requires_sync(algt->type,
                                                        algt->mask));
        if (err == -ENOENT) {
                err = -ENAMETOOLONG;
                if (snprintf(ecb_name, CRYPTO_MAX_ALG_NAME, "ecb(%s)",
                             cipher_name) >= CRYPTO_MAX_ALG_NAME)
                        goto err_free_inst;

                err = crypto_grab_skcipher(spawn, ecb_name, 0,
                                           crypto_requires_sync(algt->type,
                                                                algt->mask));
        }

        if (err)
                goto err_free_inst;

        alg = crypto_skcipher_spawn_alg(spawn);

        err = -EINVAL;
        if (alg->base.cra_blocksize != LRW_BLOCK_SIZE)
                goto err_drop_spawn;

        if (crypto_skcipher_alg_ivsize(alg))
                goto err_drop_spawn;

        err = crypto_inst_setname(skcipher_crypto_instance(inst), "lrw",
                                  &alg->base);
        if (err)
                goto err_drop_spawn;

        err = -EINVAL;
        cipher_name = alg->base.cra_name;

        /* Alas we screwed up the naming so we have to mangle the
         * cipher name.
         */
        if (!strncmp(cipher_name, "ecb(", 4)) {
                unsigned len;

                len = strlcpy(ecb_name, cipher_name + 4, sizeof(ecb_name));
                if (len < 2 || len >= sizeof(ecb_name))
                        goto err_drop_spawn;

                if (ecb_name[len - 1] != ')')
                        goto err_drop_spawn;

                ecb_name[len - 1] = 0;

                if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
                             "lrw(%s)", ecb_name) >= CRYPTO_MAX_ALG_NAME) {
                        err = -ENAMETOOLONG;
                        goto err_drop_spawn;
                }
        } else
                goto err_drop_spawn;

        inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
        inst->alg.base.cra_priority = alg->base.cra_priority;
        inst->alg.base.cra_blocksize = LRW_BLOCK_SIZE;
        inst->alg.base.cra_alignmask = alg->base.cra_alignmask |
                                       (__alignof__(__be32) - 1);

        inst->alg.ivsize = LRW_BLOCK_SIZE;
        inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg) +
                                LRW_BLOCK_SIZE;
        inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg) +
                                LRW_BLOCK_SIZE;

        inst->alg.base.cra_ctxsize = sizeof(struct priv);

        inst->alg.init = init_tfm;
        inst->alg.exit = exit_tfm;

        inst->alg.setkey = setkey;
        inst->alg.encrypt = encrypt;
        inst->alg.decrypt = decrypt;

        inst->free = free;

        err = skcipher_register_instance(tmpl, inst);
        if (err)
                goto err_drop_spawn;

out:
        return err;

err_drop_spawn:
        crypto_drop_skcipher(spawn);
err_free_inst:
        kfree(inst);
        goto out;
}

static struct crypto_template crypto_tmpl = {
        .name = "lrw",
        .create = create,
        .module = THIS_MODULE,
};

static int __init crypto_module_init(void)
{
        return crypto_register_template(&crypto_tmpl);
}

static void __exit crypto_module_exit(void)
{
        crypto_unregister_template(&crypto_tmpl);
}

module_init(crypto_module_init);
module_exit(crypto_module_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("LRW block cipher mode");
MODULE_ALIAS_CRYPTO("lrw");