/**
 * GHASH routines supporting VMX instructions on the Power 8
 *
 * Copyright (C) 2015 International Business Machines Inc.
 *
 * 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; version 2 only.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * Author: Marcelo Henrique Cerri <mhcerri@br.ibm.com>
 */

#include <linux/types.h>
#include <linux/err.h>
#include <linux/crypto.h>
#include <linux/delay.h>
#include <linux/hardirq.h>
#include <asm/switch_to.h>
#include <crypto/aes.h>
#include <crypto/scatterwalk.h>
#include <crypto/internal/hash.h>
#include <crypto/b128ops.h>

#define IN_INTERRUPT in_interrupt()

#define GHASH_BLOCK_SIZE (16)
#define GHASH_DIGEST_SIZE (16)
#define GHASH_KEY_LEN (16)

void gcm_init_p8(u128 htable[16], const u64 Xi[2]);
void gcm_gmult_p8(u64 Xi[2], const u128 htable[16]);
void gcm_ghash_p8(u64 Xi[2], const u128 htable[16],
        const u8 *in,size_t len);

struct p8_ghash_ctx {
    u128 htable[16];
    struct crypto_shash *fallback;
};

struct p8_ghash_desc_ctx {
    u64 shash[2];
    u8 buffer[GHASH_DIGEST_SIZE];
    int bytes;
    struct shash_desc fallback_desc;
};

static int p8_ghash_init_tfm(struct crypto_tfm *tfm)
{
    const char *alg;
    struct crypto_shash *fallback;
    struct crypto_shash *shash_tfm = __crypto_shash_cast(tfm);
    struct p8_ghash_ctx *ctx = crypto_tfm_ctx(tfm);

    if (!(alg = crypto_tfm_alg_name(tfm))) {
        printk(KERN_ERR "Failed to get algorithm name.\n");
        return -ENOENT;
    }

    fallback = crypto_alloc_shash(alg, 0 ,CRYPTO_ALG_NEED_FALLBACK);
    if (IS_ERR(fallback)) {
        printk(KERN_ERR "Failed to allocate transformation for '%s': %ld\n",
                alg, PTR_ERR(fallback));
        return PTR_ERR(fallback);
    }
    printk(KERN_INFO "Using '%s' as fallback implementation.\n",
            crypto_tfm_alg_driver_name(crypto_shash_tfm(fallback)));

    crypto_shash_set_flags(fallback,
            crypto_shash_get_flags((struct crypto_shash *) tfm));
    ctx->fallback = fallback;

    shash_tfm->descsize = sizeof(struct p8_ghash_desc_ctx)
        + crypto_shash_descsize(fallback);

    return 0;
}

static void p8_ghash_exit_tfm(struct crypto_tfm *tfm)
{
    struct p8_ghash_ctx *ctx = crypto_tfm_ctx(tfm);

    if (ctx->fallback) {
        crypto_free_shash(ctx->fallback);
        ctx->fallback = NULL;
    }
}

static int p8_ghash_init(struct shash_desc *desc)
{
    struct p8_ghash_ctx *ctx = crypto_tfm_ctx(crypto_shash_tfm(desc->tfm));
    struct p8_ghash_desc_ctx *dctx = shash_desc_ctx(desc);

    dctx->bytes = 0;
    memset(dctx->shash, 0, GHASH_DIGEST_SIZE);
    dctx->fallback_desc.tfm = ctx->fallback;
    dctx->fallback_desc.flags = desc->flags;
    return crypto_shash_init(&dctx->fallback_desc);
}

static int p8_ghash_setkey(struct crypto_shash *tfm, const u8 *key,
    unsigned int keylen)
{
    struct p8_ghash_ctx *ctx = crypto_tfm_ctx(crypto_shash_tfm(tfm));

    if (keylen != GHASH_KEY_LEN)
        return -EINVAL;

    pagefault_disable();
    enable_kernel_altivec();
    enable_kernel_fp();
    gcm_init_p8(ctx->htable, (const u64 *) key);
    pagefault_enable();
    return crypto_shash_setkey(ctx->fallback, key, keylen);
}

static int p8_ghash_update(struct shash_desc *desc,
        const u8 *src, unsigned int srclen)
{
    unsigned int len;
    struct p8_ghash_ctx *ctx = crypto_tfm_ctx(crypto_shash_tfm(desc->tfm));
    struct p8_ghash_desc_ctx *dctx = shash_desc_ctx(desc);

    if (IN_INTERRUPT) {
        return crypto_shash_update(&dctx->fallback_desc, src, srclen);
    } else {
        if (dctx->bytes) {
            if (dctx->bytes + srclen < GHASH_DIGEST_SIZE) {
                memcpy(dctx->buffer + dctx->bytes, src, srclen);
                dctx->bytes += srclen;
                return 0;
            }
            memcpy(dctx->buffer + dctx->bytes, src,
                    GHASH_DIGEST_SIZE - dctx->bytes);
            pagefault_disable();
            enable_kernel_altivec();
            enable_kernel_fp();
            gcm_ghash_p8(dctx->shash, ctx->htable, dctx->buffer,
                    GHASH_DIGEST_SIZE);
            pagefault_enable();
            src += GHASH_DIGEST_SIZE - dctx->bytes;
            srclen -= GHASH_DIGEST_SIZE - dctx->bytes;
            dctx->bytes = 0;
        }
        len = srclen & ~(GHASH_DIGEST_SIZE - 1);
        if (len) {
            pagefault_disable();
            enable_kernel_altivec();
            enable_kernel_fp();
            gcm_ghash_p8(dctx->shash, ctx->htable, src, len);
            pagefault_enable();
            src += len;
            srclen -= len;
        }
        if (srclen) {
            memcpy(dctx->buffer, src, srclen);
            dctx->bytes = srclen;
        }
        return 0;
    }
}

static int p8_ghash_final(struct shash_desc *desc, u8 *out)
{
    int i;
    struct p8_ghash_ctx *ctx = crypto_tfm_ctx(crypto_shash_tfm(desc->tfm));
    struct p8_ghash_desc_ctx *dctx = shash_desc_ctx(desc);

    if (IN_INTERRUPT) {
        return crypto_shash_final(&dctx->fallback_desc, out);
    } else {
        if (dctx->bytes) {
            for (i = dctx->bytes; i < GHASH_DIGEST_SIZE; i++)
                dctx->buffer[i] = 0;
            pagefault_disable();
            enable_kernel_altivec();
            enable_kernel_fp();
            gcm_ghash_p8(dctx->shash, ctx->htable, dctx->buffer,
                    GHASH_DIGEST_SIZE);
            pagefault_enable();
            dctx->bytes = 0;
        }
        memcpy(out, dctx->shash, GHASH_DIGEST_SIZE);
        return 0;
    }
}

struct shash_alg p8_ghash_alg = {
    .digestsize = GHASH_DIGEST_SIZE,
    .init       = p8_ghash_init,
    .update     = p8_ghash_update,
    .final      = p8_ghash_final,
    .setkey     = p8_ghash_setkey,
    .descsize   = sizeof(struct p8_ghash_desc_ctx),
    .base       = {
        .cra_name = "ghash",
        .cra_driver_name = "p8_ghash",
        .cra_priority = 1000,
        .cra_flags = CRYPTO_ALG_TYPE_SHASH | CRYPTO_ALG_NEED_FALLBACK,
        .cra_blocksize = GHASH_BLOCK_SIZE,
        .cra_ctxsize = sizeof(struct p8_ghash_ctx),
        .cra_module = THIS_MODULE,
        .cra_init = p8_ghash_init_tfm,
        .cra_exit = p8_ghash_exit_tfm,
    },
};