// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * ChaCha20-Poly1305 AEAD, RFC7539
 *
 * Copyright (C) 2015 Martin Willi
 */

#include <crypto/internal/aead.h>
#include <crypto/internal/hash.h>
#include <crypto/internal/skcipher.h>
#include <crypto/scatterwalk.h>
#include <crypto/chacha.h>
#include <crypto/poly1305.h>
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/string.h>

struct chachapoly_instance_ctx {
        struct crypto_skcipher_spawn chacha;
        unsigned int saltlen;
};

struct chachapoly_ctx {
        struct crypto_skcipher *chacha;
        /* key bytes we use for the ChaCha20 IV */
        unsigned int saltlen;
        u8 salt[] __counted_by(saltlen);
};

struct chacha_req {
        u8 iv[CHACHA_IV_SIZE];
        struct scatterlist src[1];
        struct skcipher_request req; /* must be last member */
};

struct chachapoly_req_ctx {
        struct scatterlist src[2];
        struct scatterlist dst[2];
        /* the key we generate for Poly1305 using Chacha20 */
        u8 key[POLY1305_KEY_SIZE];
        /* calculated Poly1305 tag */
        u8 tag[POLY1305_DIGEST_SIZE];
        /* length of data to en/decrypt, without ICV */
        unsigned int cryptlen;
        /* Actual AD, excluding IV */
        unsigned int assoclen;
        /* request flags, with MAY_SLEEP cleared if needed */
        u32 flags;
        union {
                struct chacha_req chacha;
        } u;
};

static inline void async_done_continue(struct aead_request *req, int err,
                                       int (*cont)(struct aead_request *))
{
        if (!err) {
                struct chachapoly_req_ctx *rctx = aead_request_ctx(req);

                rctx->flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
                err = cont(req);
        }

        if (err != -EINPROGRESS && err != -EBUSY)
                aead_request_complete(req, err);
}

static void chacha_iv(u8 *iv, struct aead_request *req, u32 icb)
{
        struct chachapoly_ctx *ctx = crypto_aead_ctx(crypto_aead_reqtfm(req));
        __le32 leicb = cpu_to_le32(icb);

        memcpy(iv, &leicb, sizeof(leicb));
        memcpy(iv + sizeof(leicb), ctx->salt, ctx->saltlen);
        memcpy(iv + sizeof(leicb) + ctx->saltlen, req->iv,
               CHACHA_IV_SIZE - sizeof(leicb) - ctx->saltlen);
}

static int poly_verify_tag(struct aead_request *req)
{
        struct chachapoly_req_ctx *rctx = aead_request_ctx(req);
        u8 tag[sizeof(rctx->tag)];

        scatterwalk_map_and_copy(tag, req->src,
                                 req->assoclen + rctx->cryptlen,
                                 sizeof(tag), 0);
        if (crypto_memneq(tag, rctx->tag, sizeof(tag)))
                return -EBADMSG;
        return 0;
}

static void chacha_decrypt_done(void *data, int err)
{
        async_done_continue(data, err, poly_verify_tag);
}

static int chacha_decrypt(struct aead_request *req)
{
        struct chachapoly_ctx *ctx = crypto_aead_ctx(crypto_aead_reqtfm(req));
        struct chachapoly_req_ctx *rctx = aead_request_ctx(req);
        struct chacha_req *creq = &rctx->u.chacha;
        struct scatterlist *src, *dst;
        int err;

        if (rctx->cryptlen == 0)
                goto skip;

        chacha_iv(creq->iv, req, 1);

        src = scatterwalk_ffwd(rctx->src, req->src, req->assoclen);
        dst = src;
        if (req->src != req->dst)
                dst = scatterwalk_ffwd(rctx->dst, req->dst, req->assoclen);

        skcipher_request_set_callback(&creq->req, rctx->flags,
                                      chacha_decrypt_done, req);
        skcipher_request_set_tfm(&creq->req, ctx->chacha);
        skcipher_request_set_crypt(&creq->req, src, dst,
                                   rctx->cryptlen, creq->iv);
        err = crypto_skcipher_decrypt(&creq->req);
        if (err)
                return err;

skip:
        return poly_verify_tag(req);
}

static int poly_hash(struct aead_request *req)
{
        struct chachapoly_req_ctx *rctx = aead_request_ctx(req);
        const void *zp = page_address(ZERO_PAGE(0));
        struct scatterlist *sg = req->src;
        struct poly1305_desc_ctx desc;
        struct scatter_walk walk;
        struct {
                union {
                        struct {
                                __le64 assoclen;
                                __le64 cryptlen;
                        };
                        u8 u8[16];
                };
        } tail;
        unsigned int padlen;
        unsigned int total;

        if (sg != req->dst)
                memcpy_sglist(req->dst, sg, req->assoclen);

        if (rctx->cryptlen == req->cryptlen) /* encrypting */
                sg = req->dst;

        poly1305_init(&desc, rctx->key);
        scatterwalk_start(&walk, sg);

        total = rctx->assoclen;
        while (total) {
                unsigned int n = scatterwalk_next(&walk, total);

                poly1305_update(&desc, walk.addr, n);
                scatterwalk_done_src(&walk, n);
                total -= n;
        }

        padlen = -rctx->assoclen % POLY1305_BLOCK_SIZE;
        poly1305_update(&desc, zp, padlen);

        scatterwalk_skip(&walk, req->assoclen - rctx->assoclen);

        total = rctx->cryptlen;
        while (total) {
                unsigned int n = scatterwalk_next(&walk, total);

                poly1305_update(&desc, walk.addr, n);
                scatterwalk_done_src(&walk, n);
                total -= n;
        }

        padlen = -rctx->cryptlen % POLY1305_BLOCK_SIZE;
        poly1305_update(&desc, zp, padlen);

        tail.assoclen = cpu_to_le64(rctx->assoclen);
        tail.cryptlen = cpu_to_le64(rctx->cryptlen);
        poly1305_update(&desc, tail.u8, sizeof(tail));
        memzero_explicit(&tail, sizeof(tail));
        poly1305_final(&desc, rctx->tag);

        if (rctx->cryptlen != req->cryptlen)
                return chacha_decrypt(req);

        memcpy_to_scatterwalk(&walk, rctx->tag, sizeof(rctx->tag));
        return 0;
}

static void poly_genkey_done(void *data, int err)
{
        async_done_continue(data, err, poly_hash);
}

static int poly_genkey(struct aead_request *req)
{
        struct crypto_aead *tfm = crypto_aead_reqtfm(req);
        struct chachapoly_ctx *ctx = crypto_aead_ctx(tfm);
        struct chachapoly_req_ctx *rctx = aead_request_ctx(req);
        struct chacha_req *creq = &rctx->u.chacha;
        int err;

        rctx->assoclen = req->assoclen;

        if (crypto_aead_ivsize(tfm) == 8) {
                if (rctx->assoclen < 8)
                        return -EINVAL;
                rctx->assoclen -= 8;
        }

        memset(rctx->key, 0, sizeof(rctx->key));
        sg_init_one(creq->src, rctx->key, sizeof(rctx->key));

        chacha_iv(creq->iv, req, 0);

        skcipher_request_set_callback(&creq->req, rctx->flags,
                                      poly_genkey_done, req);
        skcipher_request_set_tfm(&creq->req, ctx->chacha);
        skcipher_request_set_crypt(&creq->req, creq->src, creq->src,
                                   POLY1305_KEY_SIZE, creq->iv);

        err = crypto_skcipher_decrypt(&creq->req);
        if (err)
                return err;

        return poly_hash(req);
}

static void chacha_encrypt_done(void *data, int err)
{
        async_done_continue(data, err, poly_genkey);
}

static int chacha_encrypt(struct aead_request *req)
{
        struct chachapoly_ctx *ctx = crypto_aead_ctx(crypto_aead_reqtfm(req));
        struct chachapoly_req_ctx *rctx = aead_request_ctx(req);
        struct chacha_req *creq = &rctx->u.chacha;
        struct scatterlist *src, *dst;
        int err;

        if (req->cryptlen == 0)
                goto skip;

        chacha_iv(creq->iv, req, 1);

        src = scatterwalk_ffwd(rctx->src, req->src, req->assoclen);
        dst = src;
        if (req->src != req->dst)
                dst = scatterwalk_ffwd(rctx->dst, req->dst, req->assoclen);

        skcipher_request_set_callback(&creq->req, rctx->flags,
                                      chacha_encrypt_done, req);
        skcipher_request_set_tfm(&creq->req, ctx->chacha);
        skcipher_request_set_crypt(&creq->req, src, dst,
                                   req->cryptlen, creq->iv);
        err = crypto_skcipher_encrypt(&creq->req);
        if (err)
                return err;

skip:
        return poly_genkey(req);
}

static int chachapoly_encrypt(struct aead_request *req)
{
        struct chachapoly_req_ctx *rctx = aead_request_ctx(req);

        rctx->cryptlen = req->cryptlen;
        rctx->flags = aead_request_flags(req);

        /* encrypt call chain:
         * - chacha_encrypt/done()
         * - poly_genkey/done()
         * - poly_hash()
         */
        return chacha_encrypt(req);
}

static int chachapoly_decrypt(struct aead_request *req)
{
        struct chachapoly_req_ctx *rctx = aead_request_ctx(req);

        rctx->cryptlen = req->cryptlen - POLY1305_DIGEST_SIZE;
        rctx->flags = aead_request_flags(req);

        /* decrypt call chain:
         * - poly_genkey/done()
         * - poly_hash()
         * - chacha_decrypt/done()
         * - poly_verify_tag()
         */
        return poly_genkey(req);
}

static int chachapoly_setkey(struct crypto_aead *aead, const u8 *key,
                             unsigned int keylen)
{
        struct chachapoly_ctx *ctx = crypto_aead_ctx(aead);

        if (keylen != ctx->saltlen + CHACHA_KEY_SIZE)
                return -EINVAL;

        keylen -= ctx->saltlen;
        memcpy(ctx->salt, key + keylen, ctx->saltlen);

        crypto_skcipher_clear_flags(ctx->chacha, CRYPTO_TFM_REQ_MASK);
        crypto_skcipher_set_flags(ctx->chacha, crypto_aead_get_flags(aead) &
                                               CRYPTO_TFM_REQ_MASK);
        return crypto_skcipher_setkey(ctx->chacha, key, keylen);
}

static int chachapoly_setauthsize(struct crypto_aead *tfm,
                                  unsigned int authsize)
{
        if (authsize != POLY1305_DIGEST_SIZE)
                return -EINVAL;

        return 0;
}

static int chachapoly_init(struct crypto_aead *tfm)
{
        struct aead_instance *inst = aead_alg_instance(tfm);
        struct chachapoly_instance_ctx *ictx = aead_instance_ctx(inst);
        struct chachapoly_ctx *ctx = crypto_aead_ctx(tfm);
        struct crypto_skcipher *chacha;
        unsigned long align;

        chacha = crypto_spawn_skcipher(&ictx->chacha);
        if (IS_ERR(chacha))
                return PTR_ERR(chacha);

        ctx->chacha = chacha;
        ctx->saltlen = ictx->saltlen;

        align = crypto_aead_alignmask(tfm);
        align &= ~(crypto_tfm_ctx_alignment() - 1);
        crypto_aead_set_reqsize(
                tfm,
                align + offsetof(struct chachapoly_req_ctx, u) +
                offsetof(struct chacha_req, req) +
                sizeof(struct skcipher_request) +
                crypto_skcipher_reqsize(chacha));

        return 0;
}

static void chachapoly_exit(struct crypto_aead *tfm)
{
        struct chachapoly_ctx *ctx = crypto_aead_ctx(tfm);

        crypto_free_skcipher(ctx->chacha);
}

static void chachapoly_free(struct aead_instance *inst)
{
        struct chachapoly_instance_ctx *ctx = aead_instance_ctx(inst);

        crypto_drop_skcipher(&ctx->chacha);
        kfree(inst);
}

static int chachapoly_create(struct crypto_template *tmpl, struct rtattr **tb,
                             const char *name, unsigned int ivsize)
{
        u32 mask;
        struct aead_instance *inst;
        struct chachapoly_instance_ctx *ctx;
        struct skcipher_alg_common *chacha;
        int err;

        if (ivsize > CHACHAPOLY_IV_SIZE)
                return -EINVAL;

        err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_AEAD, &mask);
        if (err)
                return err;

        inst = kzalloc(sizeof(*inst) + sizeof(*ctx), GFP_KERNEL);
        if (!inst)
                return -ENOMEM;
        ctx = aead_instance_ctx(inst);
        ctx->saltlen = CHACHAPOLY_IV_SIZE - ivsize;

        err = crypto_grab_skcipher(&ctx->chacha, aead_crypto_instance(inst),
                                   crypto_attr_alg_name(tb[1]), 0, mask);
        if (err)
                goto err_free_inst;
        chacha = crypto_spawn_skcipher_alg_common(&ctx->chacha);

        err = -EINVAL;
        if (strcmp(crypto_attr_alg_name(tb[2]), "poly1305") &&
            strcmp(crypto_attr_alg_name(tb[2]), "poly1305-generic"))
                goto err_free_inst;
        /* Need 16-byte IV size, including Initial Block Counter value */
        if (chacha->ivsize != CHACHA_IV_SIZE)
                goto err_free_inst;
        /* Not a stream cipher? */
        if (chacha->base.cra_blocksize != 1)
                goto err_free_inst;

        err = -ENAMETOOLONG;
        if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
                     "%s(%s,poly1305)", name,
                     chacha->base.cra_name) >= CRYPTO_MAX_ALG_NAME)
                goto err_free_inst;
        if (snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME,
                     "%s(%s,poly1305-generic)", name,
                     chacha->base.cra_driver_name) >= CRYPTO_MAX_ALG_NAME)
                goto err_free_inst;

        inst->alg.base.cra_priority = chacha->base.cra_priority;
        inst->alg.base.cra_blocksize = 1;
        inst->alg.base.cra_alignmask = chacha->base.cra_alignmask;
        inst->alg.base.cra_ctxsize = sizeof(struct chachapoly_ctx) +
                                     ctx->saltlen;
        inst->alg.ivsize = ivsize;
        inst->alg.chunksize = chacha->chunksize;
        inst->alg.maxauthsize = POLY1305_DIGEST_SIZE;
        inst->alg.init = chachapoly_init;
        inst->alg.exit = chachapoly_exit;
        inst->alg.encrypt = chachapoly_encrypt;
        inst->alg.decrypt = chachapoly_decrypt;
        inst->alg.setkey = chachapoly_setkey;
        inst->alg.setauthsize = chachapoly_setauthsize;

        inst->free = chachapoly_free;

        err = aead_register_instance(tmpl, inst);
        if (err) {
err_free_inst:
                chachapoly_free(inst);
        }
        return err;
}

static int rfc7539_create(struct crypto_template *tmpl, struct rtattr **tb)
{
        return chachapoly_create(tmpl, tb, "rfc7539", 12);
}

static int rfc7539esp_create(struct crypto_template *tmpl, struct rtattr **tb)
{
        return chachapoly_create(tmpl, tb, "rfc7539esp", 8);
}

static struct crypto_template rfc7539_tmpls[] = {
        {
                .name = "rfc7539",
                .create = rfc7539_create,
                .module = THIS_MODULE,
        }, {
                .name = "rfc7539esp",
                .create = rfc7539esp_create,
                .module = THIS_MODULE,
        },
};

static int __init chacha20poly1305_module_init(void)
{
        return crypto_register_templates(rfc7539_tmpls,
                                         ARRAY_SIZE(rfc7539_tmpls));
}

static void __exit chacha20poly1305_module_exit(void)
{
        crypto_unregister_templates(rfc7539_tmpls,
                                    ARRAY_SIZE(rfc7539_tmpls));
}

module_init(chacha20poly1305_module_init);
module_exit(chacha20poly1305_module_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Martin Willi <martin@strongswan.org>");
MODULE_DESCRIPTION("ChaCha20-Poly1305 AEAD");
MODULE_ALIAS_CRYPTO("rfc7539");
MODULE_ALIAS_CRYPTO("rfc7539esp");