/*
 * echainiv: Encrypted Chain IV Generator
 *
 * This generator generates an IV based on a sequence number by xoring it
 * with a salt and then encrypting it with the same key as used to encrypt
 * the plain text.  This algorithm requires that the block size be equal
 * to the IV size.  It is mainly useful for CBC.
 *
 * This generator can only be used by algorithms where authentication
 * is performed after encryption (i.e., authenc).
 *
 * Copyright (c) 2015 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.
 *
 */

#include <crypto/internal/geniv.h>
#include <crypto/scatterwalk.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/spinlock.h>
#include <linux/string.h>

#define MAX_IV_SIZE 16

static DEFINE_PER_CPU(u32 [MAX_IV_SIZE / sizeof(u32)], echainiv_iv);

/* We don't care if we get preempted and read/write IVs from the next CPU. */
static void echainiv_read_iv(u8 *dst, unsigned size)
{
        u32 *a = (u32 *)dst;
        u32 __percpu *b = echainiv_iv;

        for (; size >= 4; size -= 4) {
                *a++ = this_cpu_read(*b);
                b++;
        }
}

static void echainiv_write_iv(const u8 *src, unsigned size)
{
        const u32 *a = (const u32 *)src;
        u32 __percpu *b = echainiv_iv;

        for (; size >= 4; size -= 4) {
                this_cpu_write(*b, *a);
                a++;
                b++;
        }
}

static void echainiv_encrypt_complete2(struct aead_request *req, int err)
{
        struct aead_request *subreq = aead_request_ctx(req);
        struct crypto_aead *geniv;
        unsigned int ivsize;

        if (err == -EINPROGRESS)
                return;

        if (err)
                goto out;

        geniv = crypto_aead_reqtfm(req);
        ivsize = crypto_aead_ivsize(geniv);

        echainiv_write_iv(subreq->iv, ivsize);

        if (req->iv != subreq->iv)
                memcpy(req->iv, subreq->iv, ivsize);

out:
        if (req->iv != subreq->iv)
                kzfree(subreq->iv);
}

static void echainiv_encrypt_complete(struct crypto_async_request *base,
                                         int err)
{
        struct aead_request *req = base->data;

        echainiv_encrypt_complete2(req, err);
        aead_request_complete(req, err);
}

static int echainiv_encrypt(struct aead_request *req)
{
        struct crypto_aead *geniv = crypto_aead_reqtfm(req);
        struct aead_geniv_ctx *ctx = crypto_aead_ctx(geniv);
        struct aead_request *subreq = aead_request_ctx(req);
        crypto_completion_t compl;
        void *data;
        u8 *info;
        unsigned int ivsize = crypto_aead_ivsize(geniv);
        int err;

        if (req->cryptlen < ivsize)
                return -EINVAL;

        aead_request_set_tfm(subreq, ctx->child);

        compl = echainiv_encrypt_complete;
        data = req;
        info = req->iv;

        if (req->src != req->dst) {
                struct blkcipher_desc desc = {
                        .tfm = ctx->null,
                };

                err = crypto_blkcipher_encrypt(
                        &desc, req->dst, req->src,
                        req->assoclen + req->cryptlen);
                if (err)
                        return err;
        }

        if (unlikely(!IS_ALIGNED((unsigned long)info,
                                 crypto_aead_alignmask(geniv) + 1))) {
                info = kmalloc(ivsize, req->base.flags &
                                       CRYPTO_TFM_REQ_MAY_SLEEP ? GFP_KERNEL:
                                                                  GFP_ATOMIC);
                if (!info)
                        return -ENOMEM;

                memcpy(info, req->iv, ivsize);
        }

        aead_request_set_callback(subreq, req->base.flags, compl, data);
        aead_request_set_crypt(subreq, req->dst, req->dst,
                               req->cryptlen, info);
        aead_request_set_ad(subreq, req->assoclen);

        crypto_xor(info, ctx->salt, ivsize);
        scatterwalk_map_and_copy(info, req->dst, req->assoclen, ivsize, 1);
        echainiv_read_iv(info, ivsize);

        err = crypto_aead_encrypt(subreq);
        echainiv_encrypt_complete2(req, err);
        return err;
}

static int echainiv_decrypt(struct aead_request *req)
{
        struct crypto_aead *geniv = crypto_aead_reqtfm(req);
        struct aead_geniv_ctx *ctx = crypto_aead_ctx(geniv);
        struct aead_request *subreq = aead_request_ctx(req);
        crypto_completion_t compl;
        void *data;
        unsigned int ivsize = crypto_aead_ivsize(geniv);

        if (req->cryptlen < ivsize)
                return -EINVAL;

        aead_request_set_tfm(subreq, ctx->child);

        compl = req->base.complete;
        data = req->base.data;

        aead_request_set_callback(subreq, req->base.flags, compl, data);
        aead_request_set_crypt(subreq, req->src, req->dst,
                               req->cryptlen - ivsize, req->iv);
        aead_request_set_ad(subreq, req->assoclen + ivsize);

        scatterwalk_map_and_copy(req->iv, req->src, req->assoclen, ivsize, 0);

        return crypto_aead_decrypt(subreq);
}

static int echainiv_aead_create(struct crypto_template *tmpl,
                                struct rtattr **tb)
{
        struct aead_instance *inst;
        struct crypto_aead_spawn *spawn;
        struct aead_alg *alg;
        int err;

        inst = aead_geniv_alloc(tmpl, tb, 0, 0);

        if (IS_ERR(inst))
                return PTR_ERR(inst);

        spawn = aead_instance_ctx(inst);
        alg = crypto_spawn_aead_alg(spawn);

        err = -EINVAL;
        if (inst->alg.ivsize & (sizeof(u32) - 1) ||
            inst->alg.ivsize > MAX_IV_SIZE)
                goto free_inst;

        inst->alg.encrypt = echainiv_encrypt;
        inst->alg.decrypt = echainiv_decrypt;

        inst->alg.init = aead_init_geniv;
        inst->alg.exit = aead_exit_geniv;

        inst->alg.base.cra_alignmask |= __alignof__(u32) - 1;
        inst->alg.base.cra_ctxsize = sizeof(struct aead_geniv_ctx);
        inst->alg.base.cra_ctxsize += inst->alg.ivsize;

        inst->free = aead_geniv_free;

        err = aead_register_instance(tmpl, inst);
        if (err)
                goto free_inst;

out:
        return err;

free_inst:
        aead_geniv_free(inst);
        goto out;
}

static void echainiv_free(struct crypto_instance *inst)
{
        aead_geniv_free(aead_instance(inst));
}

static struct crypto_template echainiv_tmpl = {
        .name = "echainiv",
        .create = echainiv_aead_create,
        .free = echainiv_free,
        .module = THIS_MODULE,
};

static int __init echainiv_module_init(void)
{
        return crypto_register_template(&echainiv_tmpl);
}

static void __exit echainiv_module_exit(void)
{
        crypto_unregister_template(&echainiv_tmpl);
}

module_init(echainiv_module_init);
module_exit(echainiv_module_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Encrypted Chain IV Generator");
MODULE_ALIAS_CRYPTO("echainiv");