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dm crypt: reuse eboiv skcipher for IV generation

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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>
This commit is contained in:
Ard Biesheuvel 2019-08-07 08:50:22 +03:00 committed by Mike Snitzer
parent 123d87d553
commit 39d13a1ac4
1 changed files with 26 additions and 52 deletions
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78
drivers/md/dm-crypt.c
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@ -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 (crypto_cipher_blocksize(tfm) != cc->iv_size) {
ti->error = "Block size of EBOIV cipher does "
"not match IV size of block cipher";
crypto_free_cipher(tfm);
if (test_bit(CRYPT_MODE_INTEGRITY_AEAD, &cc->cipher_flags)) {
ti->error = "AEAD transforms not supported for EBOIV";
return -EINVAL;
}
eboiv->tfm = tfm;
return 0;
}
static int crypt_iv_eboiv_init(struct crypt_config *cc)
{
struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
int err;
err = crypto_cipher_setkey(eboiv->tfm, cc->key, cc->key_size);
if (err)
return err;
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";
return -EINVAL;
}
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);
}
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;
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);
req = skcipher_request_alloc(any_tfm(cc), GFP_KERNEL | GFP_NOFS);
if (!req)
return -ENOMEM;
return 0;
memset(buf, 0, cc->iv_size);
*(__le64 *)buf = cpu_to_le64(dmreq->iv_sector * cc->sector_size);
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 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
};