// SPDX-License-Identifier: GPL-2.0-only
/*
 * POLYVAL: hash function for HCTR2.
 *
 * Copyright (c) 2007 Nokia Siemens Networks - Mikko Herranen <mh1@iki.fi>
 * Copyright (c) 2009 Intel Corp.
 *   Author: Huang Ying <ying.huang@intel.com>
 * Copyright 2021 Google LLC
 */

/*
 * Code based on crypto/ghash-generic.c
 *
 * POLYVAL is a keyed hash function similar to GHASH. POLYVAL uses a different
 * modulus for finite field multiplication which makes hardware accelerated
 * implementations on little-endian machines faster. POLYVAL is used in the
 * kernel to implement HCTR2, but was originally specified for AES-GCM-SIV
 * (RFC 8452).
 *
 * For more information see:
 * Length-preserving encryption with HCTR2:
 *   https://eprint.iacr.org/2021/1441.pdf
 * AES-GCM-SIV: Nonce Misuse-Resistant Authenticated Encryption:
 *   https://datatracker.ietf.org/doc/html/rfc8452
 *
 * Like GHASH, POLYVAL is not a cryptographic hash function and should
 * not be used outside of crypto modes explicitly designed to use POLYVAL.
 *
 * This implementation uses a convenient trick involving the GHASH and POLYVAL
 * fields. This trick allows multiplication in the POLYVAL field to be
 * implemented by using multiplication in the GHASH field as a subroutine. An
 * element of the POLYVAL field can be converted to an element of the GHASH
 * field by computing x*REVERSE(a), where REVERSE reverses the byte-ordering of
 * a. Similarly, an element of the GHASH field can be converted back to the
 * POLYVAL field by computing REVERSE(x^{-1}*a). For more information, see:
 * https://datatracker.ietf.org/doc/html/rfc8452#appendix-A
 *
 * By using this trick, we do not need to implement the POLYVAL field for the
 * generic implementation.
 *
 * Warning: this generic implementation is not intended to be used in practice
 * and is not constant time. For practical use, a hardware accelerated
 * implementation of POLYVAL should be used instead.
 *
 */

#include <asm/unaligned.h>
#include <crypto/algapi.h>
#include <crypto/gf128mul.h>
#include <crypto/polyval.h>
#include <crypto/internal/hash.h>
#include <linux/crypto.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>

struct polyval_tfm_ctx {
        struct gf128mul_4k *gf128;
};

struct polyval_desc_ctx {
        union {
                u8 buffer[POLYVAL_BLOCK_SIZE];
                be128 buffer128;
        };
        u32 bytes;
};

static void copy_and_reverse(u8 dst[POLYVAL_BLOCK_SIZE],
                             const u8 src[POLYVAL_BLOCK_SIZE])
{
        u64 a = get_unaligned((const u64 *)&src[0]);
        u64 b = get_unaligned((const u64 *)&src[8]);

        put_unaligned(swab64(a), (u64 *)&dst[8]);
        put_unaligned(swab64(b), (u64 *)&dst[0]);
}

/*
 * Performs multiplication in the POLYVAL field using the GHASH field as a
 * subroutine.  This function is used as a fallback for hardware accelerated
 * implementations when simd registers are unavailable.
 *
 * Note: This function is not used for polyval-generic, instead we use the 4k
 * lookup table implementation for finite field multiplication.
 */
void polyval_mul_non4k(u8 *op1, const u8 *op2)
{
        be128 a, b;

        // Assume one argument is in Montgomery form and one is not.
        copy_and_reverse((u8 *)&a, op1);
        copy_and_reverse((u8 *)&b, op2);
        gf128mul_x_lle(&a, &a);
        gf128mul_lle(&a, &b);
        copy_and_reverse(op1, (u8 *)&a);
}
EXPORT_SYMBOL_GPL(polyval_mul_non4k);

/*
 * Perform a POLYVAL update using non4k multiplication.  This function is used
 * as a fallback for hardware accelerated implementations when simd registers
 * are unavailable.
 *
 * Note: This function is not used for polyval-generic, instead we use the 4k
 * lookup table implementation of finite field multiplication.
 */
void polyval_update_non4k(const u8 *key, const u8 *in,
                          size_t nblocks, u8 *accumulator)
{
        while (nblocks--) {
                crypto_xor(accumulator, in, POLYVAL_BLOCK_SIZE);
                polyval_mul_non4k(accumulator, key);
                in += POLYVAL_BLOCK_SIZE;
        }
}
EXPORT_SYMBOL_GPL(polyval_update_non4k);

static int polyval_setkey(struct crypto_shash *tfm,
                          const u8 *key, unsigned int keylen)
{
        struct polyval_tfm_ctx *ctx = crypto_shash_ctx(tfm);
        be128 k;

        if (keylen != POLYVAL_BLOCK_SIZE)
                return -EINVAL;

        gf128mul_free_4k(ctx->gf128);

        BUILD_BUG_ON(sizeof(k) != POLYVAL_BLOCK_SIZE);
        copy_and_reverse((u8 *)&k, key);
        gf128mul_x_lle(&k, &k);

        ctx->gf128 = gf128mul_init_4k_lle(&k);
        memzero_explicit(&k, POLYVAL_BLOCK_SIZE);

        if (!ctx->gf128)
                return -ENOMEM;

        return 0;
}

static int polyval_init(struct shash_desc *desc)
{
        struct polyval_desc_ctx *dctx = shash_desc_ctx(desc);

        memset(dctx, 0, sizeof(*dctx));

        return 0;
}

static int polyval_update(struct shash_desc *desc,
                         const u8 *src, unsigned int srclen)
{
        struct polyval_desc_ctx *dctx = shash_desc_ctx(desc);
        const struct polyval_tfm_ctx *ctx = crypto_shash_ctx(desc->tfm);
        u8 *pos;
        u8 tmp[POLYVAL_BLOCK_SIZE];
        int n;

        if (dctx->bytes) {
                n = min(srclen, dctx->bytes);
                pos = dctx->buffer + dctx->bytes - 1;

                dctx->bytes -= n;
                srclen -= n;

                while (n--)
                        *pos-- ^= *src++;

                if (!dctx->bytes)
                        gf128mul_4k_lle(&dctx->buffer128, ctx->gf128);
        }

        while (srclen >= POLYVAL_BLOCK_SIZE) {
                copy_and_reverse(tmp, src);
                crypto_xor(dctx->buffer, tmp, POLYVAL_BLOCK_SIZE);
                gf128mul_4k_lle(&dctx->buffer128, ctx->gf128);
                src += POLYVAL_BLOCK_SIZE;
                srclen -= POLYVAL_BLOCK_SIZE;
        }

        if (srclen) {
                dctx->bytes = POLYVAL_BLOCK_SIZE - srclen;
                pos = dctx->buffer + POLYVAL_BLOCK_SIZE - 1;
                while (srclen--)
                        *pos-- ^= *src++;
        }

        return 0;
}

static int polyval_final(struct shash_desc *desc, u8 *dst)
{
        struct polyval_desc_ctx *dctx = shash_desc_ctx(desc);
        const struct polyval_tfm_ctx *ctx = crypto_shash_ctx(desc->tfm);

        if (dctx->bytes)
                gf128mul_4k_lle(&dctx->buffer128, ctx->gf128);
        copy_and_reverse(dst, dctx->buffer);
        return 0;
}

static void polyval_exit_tfm(struct crypto_tfm *tfm)
{
        struct polyval_tfm_ctx *ctx = crypto_tfm_ctx(tfm);

        gf128mul_free_4k(ctx->gf128);
}

static struct shash_alg polyval_alg = {
        .digestsize     = POLYVAL_DIGEST_SIZE,
        .init           = polyval_init,
        .update         = polyval_update,
        .final          = polyval_final,
        .setkey         = polyval_setkey,
        .descsize       = sizeof(struct polyval_desc_ctx),
        .base           = {
                .cra_name               = "polyval",
                .cra_driver_name        = "polyval-generic",
                .cra_priority           = 100,
                .cra_blocksize          = POLYVAL_BLOCK_SIZE,
                .cra_ctxsize            = sizeof(struct polyval_tfm_ctx),
                .cra_module             = THIS_MODULE,
                .cra_exit               = polyval_exit_tfm,
        },
};

static int __init polyval_mod_init(void)
{
        return crypto_register_shash(&polyval_alg);
}

static void __exit polyval_mod_exit(void)
{
        crypto_unregister_shash(&polyval_alg);
}

subsys_initcall(polyval_mod_init);
module_exit(polyval_mod_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("POLYVAL hash function");
MODULE_ALIAS_CRYPTO("polyval");
MODULE_ALIAS_CRYPTO("polyval-generic");