dm-crypt: switch to using the crc32 library

Now that the crc32() library function takes advantage of
architecture-specific optimizations, it is unnecessary to go through the
crypto API. Just use crc32(). This is much simpler, and it improves
performance due to eliminating the crypto API overhead. (However, this
only affects the TCW IV mode of dm-crypt, which is a compatibility mode
that is rarely used compared to other dm-crypt modes.)

Signed-off-by: Eric Biggers <[e-mail]>
Signed-off-by: Mikulas Patocka <[e-mail]>

drivers/md/Kconfig

···
 	depends on BLK_DEV_DM
 	depends on (ENCRYPTED_KEYS || ENCRYPTED_KEYS=n)
 	depends on (TRUSTED_KEYS || TRUSTED_KEYS=n)
+	select CRC32
 	select CRYPTO
 	select CRYPTO_CBC
 	select CRYPTO_ESSIV

drivers/md/dm-crypt.c

···
 #include <linux/bio.h>
 #include <linux/blkdev.h>
 #include <linux/blk-integrity.h>
+#include <linux/crc32.h>
 #include <linux/mempool.h>
 #include <linux/slab.h>
 #include <linux/crypto.h>
···
 
 #define TCW_WHITENING_SIZE 16
 struct iv_tcw_private {
-	struct crypto_shash *crc32_tfm;
 	u8 *iv_seed;
 	u8 *whitening;
 };
···
 	tcw->iv_seed = NULL;
 	kfree_sensitive(tcw->whitening);
 	tcw->whitening = NULL;
-
-	if (tcw->crc32_tfm && !IS_ERR(tcw->crc32_tfm))
-		crypto_free_shash(tcw->crc32_tfm);
-	tcw->crc32_tfm = NULL;
 }
 
 static int crypt_iv_tcw_ctr(struct crypt_config *cc, struct dm_target *ti,
···
 	if (cc->key_size <= (cc->iv_size + TCW_WHITENING_SIZE)) {
 		ti->error = "Wrong key size for TCW";
 		return -EINVAL;
-	}
-
-	tcw->crc32_tfm = crypto_alloc_shash("crc32", 0,
-					    CRYPTO_ALG_ALLOCATES_MEMORY);
-	if (IS_ERR(tcw->crc32_tfm)) {
-		ti->error = "Error initializing CRC32 in TCW";
-		return PTR_ERR(tcw->crc32_tfm);
 	}
 
 	tcw->iv_seed = kzalloc(cc->iv_size, GFP_KERNEL);
···
 	return 0;
 }
 
-static int crypt_iv_tcw_whitening(struct crypt_config *cc,
-				  struct dm_crypt_request *dmreq,
-				  u8 *data)
+static void crypt_iv_tcw_whitening(struct crypt_config *cc,
+				   struct dm_crypt_request *dmreq, u8 *data)
 {
 	struct iv_tcw_private *tcw = &cc->iv_gen_private.tcw;
 	__le64 sector = cpu_to_le64(dmreq->iv_sector);
 	u8 buf[TCW_WHITENING_SIZE];
-	SHASH_DESC_ON_STACK(desc, tcw->crc32_tfm);
-	int i, r;
+	int i;
 
 	/* xor whitening with sector number */
 	crypto_xor_cpy(buf, tcw->whitening, (u8 *)&sector, 8);
 	crypto_xor_cpy(&buf[8], tcw->whitening + 8, (u8 *)&sector, 8);
 
 	/* calculate crc32 for every 32bit part and xor it */
-	desc->tfm = tcw->crc32_tfm;
-	for (i = 0; i < 4; i++) {
-		r = crypto_shash_digest(desc, &buf[i * 4], 4, &buf[i * 4]);
-		if (r)
-			goto out;
-	}
+	for (i = 0; i < 4; i++)
+		put_unaligned_le32(crc32(0, &buf[i * 4], 4), &buf[i * 4]);
 	crypto_xor(&buf[0], &buf[12], 4);
 	crypto_xor(&buf[4], &buf[8], 4);
 
 	/* apply whitening (8 bytes) to whole sector */
 	for (i = 0; i < ((1 << SECTOR_SHIFT) / 8); i++)
 		crypto_xor(data + i * 8, buf, 8);
-out:
 	memzero_explicit(buf, sizeof(buf));
-	return r;
 }
 
 static int crypt_iv_tcw_gen(struct crypt_config *cc, u8 *iv,
···
 	struct iv_tcw_private *tcw = &cc->iv_gen_private.tcw;
 	__le64 sector = cpu_to_le64(dmreq->iv_sector);
 	u8 *src;
-	int r = 0;
 
 	/* Remove whitening from ciphertext */
 	if (bio_data_dir(dmreq->ctx->bio_in) != WRITE) {
 		sg = crypt_get_sg_data(cc, dmreq->sg_in);
 		src = kmap_local_page(sg_page(sg));
-		r = crypt_iv_tcw_whitening(cc, dmreq, src + sg->offset);
+		crypt_iv_tcw_whitening(cc, dmreq, src + sg->offset);
 		kunmap_local(src);
 	}
 
···
 		crypto_xor_cpy(&iv[8], tcw->iv_seed + 8, (u8 *)&sector,
 			       cc->iv_size - 8);
 
-	return r;
+	return 0;
 }
 
 static int crypt_iv_tcw_post(struct crypt_config *cc, u8 *iv,
···
 {
 	struct scatterlist *sg;
 	u8 *dst;
-	int r;
 
 	if (bio_data_dir(dmreq->ctx->bio_in) != WRITE)
 		return 0;
···
 	/* Apply whitening on ciphertext */
 	sg = crypt_get_sg_data(cc, dmreq->sg_out);
 	dst = kmap_local_page(sg_page(sg));
-	r = crypt_iv_tcw_whitening(cc, dmreq, dst + sg->offset);
+	crypt_iv_tcw_whitening(cc, dmreq, dst + sg->offset);
 	kunmap_local(dst);
 
-	return r;
+	return 0;
 }
 
 static int crypt_iv_random_gen(struct crypt_config *cc, u8 *iv,