crc32c.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Cryptographic API.
 *
 * CRC32C chksum
 *
 *@Article{castagnoli-crc,
 * author =       { Guy Castagnoli and Stefan Braeuer and Martin Herrman},
 * title =        {{Optimization of Cyclic Redundancy-Check Codes with 24
 *                 and 32 Parity Bits}},
 * journal =      IEEE Transactions on Communication,
 * year =         {1993},
 * volume =       {41},
 * number =       {6},
 * pages =        {},
 * month =        {June},
 *}
 * Used by the iSCSI driver, possibly others, and derived from
 * the iscsi-crc.c module of the linux-iscsi driver at
 * http://linux-iscsi.sourceforge.net.
 *
 * Following the example of lib/crc32, this function is intended to be
 * flexible and useful for all users.  Modules that currently have their
 * own crc32c, but hopefully may be able to use this one are:
 *  net/sctp (please add all your doco to here if you change to
 *            use this one!)
 *  <endoflist>
 *
 * Copyright (c) 2004 Cisco Systems, Inc.
 * Copyright (c) 2008 Herbert Xu <[email protected]>
 */

#include <linux/unaligned.h>
#include <crypto/internal/hash.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/crc32.h>

#define CHKSUM_BLOCK_SIZE	1
#define CHKSUM_DIGEST_SIZE	4

struct chksum_ctx {
	u32 key;
};

struct chksum_desc_ctx {
	u32 crc;
};

/*
 * Steps through buffer one byte at a time, calculates reflected
 * crc using table.
 */

static int chksum_init(struct shash_desc *desc)
{
	struct chksum_ctx *mctx = crypto_shash_ctx(desc->tfm);
	struct chksum_desc_ctx *ctx = shash_desc_ctx(desc);

	ctx->crc = mctx->key;

	return 0;
}

/*
 * Setting the seed allows arbitrary accumulators and flexible XOR policy
 * If your algorithm starts with ~0, then XOR with ~0 before you set
 * the seed.
 */
static int chksum_setkey(struct crypto_shash *tfm, const u8 *key,
			 unsigned int keylen)
{
	struct chksum_ctx *mctx = crypto_shash_ctx(tfm);

	if (keylen != sizeof(mctx->key))
		return -EINVAL;
	mctx->key = get_unaligned_le32(key);
	return 0;
}

static int chksum_update(struct shash_desc *desc, const u8 *data,
			 unsigned int length)
{
	struct chksum_desc_ctx *ctx = shash_desc_ctx(desc);

	ctx->crc = crc32c(ctx->crc, data, length);
	return 0;
}

static int chksum_final(struct shash_desc *desc, u8 *out)
{
	struct chksum_desc_ctx *ctx = shash_desc_ctx(desc);

	put_unaligned_le32(~ctx->crc, out);
	return 0;
}

static int __chksum_finup(u32 *crcp, const u8 *data, unsigned int len, u8 *out)
{
	put_unaligned_le32(~crc32c(*crcp, data, len), out);
	return 0;
}

static int chksum_finup(struct shash_desc *desc, const u8 *data,
			unsigned int len, u8 *out)
{
	struct chksum_desc_ctx *ctx = shash_desc_ctx(desc);

	return __chksum_finup(&ctx->crc, data, len, out);
}

static int chksum_digest(struct shash_desc *desc, const u8 *data,
			 unsigned int length, u8 *out)
{
	struct chksum_ctx *mctx = crypto_shash_ctx(desc->tfm);

	return __chksum_finup(&mctx->key, data, length, out);
}

static int crc32c_cra_init(struct crypto_tfm *tfm)
{
	struct chksum_ctx *mctx = crypto_tfm_ctx(tfm);

	mctx->key = ~0;
	return 0;
}

static struct shash_alg alg = {
	.digestsize		= CHKSUM_DIGEST_SIZE,
	.setkey			= chksum_setkey,
	.init			= chksum_init,
	.update			= chksum_update,
	.final			= chksum_final,
	.finup			= chksum_finup,
	.digest			= chksum_digest,
	.descsize		= sizeof(struct chksum_desc_ctx),

	.base.cra_name		= "crc32c",
	.base.cra_driver_name	= "crc32c-lib",
	.base.cra_priority	= 100,
	.base.cra_flags		= CRYPTO_ALG_OPTIONAL_KEY,
	.base.cra_blocksize	= CHKSUM_BLOCK_SIZE,
	.base.cra_ctxsize	= sizeof(struct chksum_ctx),
	.base.cra_module	= THIS_MODULE,
	.base.cra_init		= crc32c_cra_init,
};

static int __init crc32c_mod_init(void)
{
	return crypto_register_shash(&alg);
}

static void __exit crc32c_mod_fini(void)
{
	crypto_unregister_shash(&alg);
}

module_init(crc32c_mod_init);
module_exit(crc32c_mod_fini);

MODULE_AUTHOR("Clay Haapala <[email protected]>");
MODULE_DESCRIPTION("CRC32c (Castagnoli) calculations wrapper for lib/crc32c");
MODULE_LICENSE("GPL");
MODULE_ALIAS_CRYPTO("crc32c");