dm crypt: reuse eboiv skcipher for IV generation

Instead of instantiating a separate cipher to perform the encryption
needed to produce the IV, reuse the skcipher used for the block data
and invoke it one additional time for each block to encrypt a zero
vector and use the output as the IV.

For CBC mode, this is equivalent to using the bare block cipher, but
without the risk of ending up with a non-time invariant implementation
of AES when the skcipher itself is time variant (e.g., arm64 without
Crypto Extensions has a NEON based time invariant implementation of
cbc(aes) but no time invariant implementation of the core cipher other
than aes-ti, which is not enabled by default).

This approach is a compromise between dm-crypt API flexibility and
reducing dependence on parts of the crypto API that should not usually
be exposed to other subsystems, such as the bare cipher API.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Milan Broz <gmazyland@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index d5216bc..48cd76c 100644 (file)
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -120,10 +120,6 @@ struct iv_tcw_private {
        u8 *whitening;
 };
 
-struct iv_eboiv_private {
-       struct crypto_cipher *tfm;
-};
-
 /*
  * Crypt: maps a linear range of a block device
  * and encrypts / decrypts at the same time.
@@ -163,7 +159,6 @@ struct crypt_config {
                struct iv_benbi_private benbi;
                struct iv_lmk_private lmk;
                struct iv_tcw_private tcw;
-               struct iv_eboiv_private eboiv;
        } iv_gen_private;
        u64 iv_offset;
        unsigned int iv_size;
@@ -847,65 +842,47 @@ static int crypt_iv_random_gen(struct crypt_config *cc, u8 *iv,
        return 0;
 }
 
-static void crypt_iv_eboiv_dtr(struct crypt_config *cc)
-{
-       struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
-
-       crypto_free_cipher(eboiv->tfm);
-       eboiv->tfm = NULL;
-}
-
 static int crypt_iv_eboiv_ctr(struct crypt_config *cc, struct dm_target *ti,
                            const char *opts)
 {
-       struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
-       struct crypto_cipher *tfm;
-
-       tfm = crypto_alloc_cipher(cc->cipher, 0, 0);
-       if (IS_ERR(tfm)) {
-               ti->error = "Error allocating crypto tfm for EBOIV";
-               return PTR_ERR(tfm);
+       if (test_bit(CRYPT_MODE_INTEGRITY_AEAD, &cc->cipher_flags)) {
+               ti->error = "AEAD transforms not supported for EBOIV";
+               return -EINVAL;
        }
 
-       if (crypto_cipher_blocksize(tfm) != cc->iv_size) {
+       if (crypto_skcipher_blocksize(any_tfm(cc)) != cc->iv_size) {
                ti->error = "Block size of EBOIV cipher does "
                            "not match IV size of block cipher";
-               crypto_free_cipher(tfm);
                return -EINVAL;
        }
 
-       eboiv->tfm = tfm;
        return 0;
 }
 
-static int crypt_iv_eboiv_init(struct crypt_config *cc)
+static int crypt_iv_eboiv_gen(struct crypt_config *cc, u8 *iv,
+                           struct dm_crypt_request *dmreq)
 {
-       struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
+       u8 buf[MAX_CIPHER_BLOCKSIZE] __aligned(__alignof__(__le64));
+       struct skcipher_request *req;
+       struct scatterlist src, dst;
+       struct crypto_wait wait;
        int err;
 
-       err = crypto_cipher_setkey(eboiv->tfm, cc->key, cc->key_size);
-       if (err)
-               return err;
-
-       return 0;
-}
-
-static int crypt_iv_eboiv_wipe(struct crypt_config *cc)
-{
-       /* Called after cc->key is set to random key in crypt_wipe() */
-       return crypt_iv_eboiv_init(cc);
-}
+       req = skcipher_request_alloc(any_tfm(cc), GFP_KERNEL | GFP_NOFS);
+       if (!req)
+               return -ENOMEM;
 
-static int crypt_iv_eboiv_gen(struct crypt_config *cc, u8 *iv,
-                           struct dm_crypt_request *dmreq)
-{
-       struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
+       memset(buf, 0, cc->iv_size);
+       *(__le64 *)buf = cpu_to_le64(dmreq->iv_sector * cc->sector_size);
 
-       memset(iv, 0, cc->iv_size);
-       *(__le64 *)iv = cpu_to_le64(dmreq->iv_sector * cc->sector_size);
-       crypto_cipher_encrypt_one(eboiv->tfm, iv, iv);
+       sg_init_one(&src, page_address(ZERO_PAGE(0)), cc->iv_size);
+       sg_init_one(&dst, iv, cc->iv_size);
+       skcipher_request_set_crypt(req, &src, &dst, cc->iv_size, buf);
+       skcipher_request_set_callback(req, 0, crypto_req_done, &wait);
+       err = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
+       skcipher_request_free(req);
 
-       return 0;
+       return err;
 }
 
 static const struct crypt_iv_operations crypt_iv_plain_ops = {
@@ -962,9 +939,6 @@ static struct crypt_iv_operations crypt_iv_random_ops = {
 
 static struct crypt_iv_operations crypt_iv_eboiv_ops = {
        .ctr       = crypt_iv_eboiv_ctr,
-       .dtr       = crypt_iv_eboiv_dtr,
-       .init      = crypt_iv_eboiv_init,
-       .wipe      = crypt_iv_eboiv_wipe,
        .generator = crypt_iv_eboiv_gen
 };