linux/crypto/xts.c
Ondrej Mosnacek 78105c7e76 crypto: xts - Drop use of auxiliary buffer
Since commit acb9b159c7 ("crypto: gf128mul - define gf128mul_x_* in
gf128mul.h"), the gf128mul_x_*() functions are very fast and therefore
caching the computed XTS tweaks has only negligible advantage over
computing them twice.

In fact, since the current caching implementation limits the size of
the calls to the child ecb(...) algorithm to PAGE_SIZE (usually 4096 B),
it is often actually slower than the simple recomputing implementation.

This patch simplifies the XTS template to recompute the XTS tweaks from
scratch in the second pass and thus also removes the need to allocate a
dynamic buffer using kmalloc().

As discussed at [1], the use of kmalloc causes deadlocks with dm-crypt.

PERFORMANCE RESULTS
I measured time to encrypt/decrypt a memory buffer of varying sizes with
xts(ecb-aes-aesni) using a tool I wrote ([2]) and the results suggest
that after this patch the performance is either better or comparable for
both small and large buffers. Note that there is a lot of noise in the
measurements, but the overall difference is easy to see.

Old code:
       ALGORITHM KEY (b)        DATA (B)   TIME ENC (ns)   TIME DEC (ns)
        xts(aes)     256              64             331             328
        xts(aes)     384              64             332             333
        xts(aes)     512              64             338             348
        xts(aes)     256             512             889             920
        xts(aes)     384             512            1019             993
        xts(aes)     512             512            1032             990
        xts(aes)     256            4096            2152            2292
        xts(aes)     384            4096            2453            2597
        xts(aes)     512            4096            3041            2641
        xts(aes)     256           16384            9443            8027
        xts(aes)     384           16384            8536            8925
        xts(aes)     512           16384            9232            9417
        xts(aes)     256           32768           16383           14897
        xts(aes)     384           32768           17527           16102
        xts(aes)     512           32768           18483           17322

New code:
       ALGORITHM KEY (b)        DATA (B)   TIME ENC (ns)   TIME DEC (ns)
        xts(aes)     256              64             328             324
        xts(aes)     384              64             324             319
        xts(aes)     512              64             320             322
        xts(aes)     256             512             476             473
        xts(aes)     384             512             509             492
        xts(aes)     512             512             531             514
        xts(aes)     256            4096            2132            1829
        xts(aes)     384            4096            2357            2055
        xts(aes)     512            4096            2178            2027
        xts(aes)     256           16384            6920            6983
        xts(aes)     384           16384            8597            7505
        xts(aes)     512           16384            7841            8164
        xts(aes)     256           32768           13468           12307
        xts(aes)     384           32768           14808           13402
        xts(aes)     512           32768           15753           14636

[1] https://lkml.org/lkml/2018/8/23/1315
[2] https://gitlab.com/omos/linux-crypto-bench

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2018-09-21 13:24:50 +08:00

368 lines
9.0 KiB
C

/* XTS: as defined in IEEE1619/D16
* http://grouper.ieee.org/groups/1619/email/pdf00086.pdf
* (sector sizes which are not a multiple of 16 bytes are,
* however currently unsupported)
*
* Copyright (c) 2007 Rik Snel <rsnel@cube.dyndns.org>
*
* Based on ecb.c
* Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
*
* 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; either version 2 of the License, or (at your option)
* any later version.
*/
#include <crypto/internal/skcipher.h>
#include <crypto/scatterwalk.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/scatterlist.h>
#include <linux/slab.h>
#include <crypto/xts.h>
#include <crypto/b128ops.h>
#include <crypto/gf128mul.h>
struct priv {
struct crypto_skcipher *child;
struct crypto_cipher *tweak;
};
struct xts_instance_ctx {
struct crypto_skcipher_spawn spawn;
char name[CRYPTO_MAX_ALG_NAME];
};
struct rctx {
le128 t;
struct skcipher_request subreq;
};
static int setkey(struct crypto_skcipher *parent, const u8 *key,
unsigned int keylen)
{
struct priv *ctx = crypto_skcipher_ctx(parent);
struct crypto_skcipher *child;
struct crypto_cipher *tweak;
int err;
err = xts_verify_key(parent, key, keylen);
if (err)
return err;
keylen /= 2;
/* we need two cipher instances: one to compute the initial 'tweak'
* by encrypting the IV (usually the 'plain' iv) and the other
* one to encrypt and decrypt the data */
/* tweak cipher, uses Key2 i.e. the second half of *key */
tweak = ctx->tweak;
crypto_cipher_clear_flags(tweak, CRYPTO_TFM_REQ_MASK);
crypto_cipher_set_flags(tweak, crypto_skcipher_get_flags(parent) &
CRYPTO_TFM_REQ_MASK);
err = crypto_cipher_setkey(tweak, key + keylen, keylen);
crypto_skcipher_set_flags(parent, crypto_cipher_get_flags(tweak) &
CRYPTO_TFM_RES_MASK);
if (err)
return err;
/* data cipher, uses Key1 i.e. the first half of *key */
child = ctx->child;
crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
CRYPTO_TFM_REQ_MASK);
err = crypto_skcipher_setkey(child, key, keylen);
crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) &
CRYPTO_TFM_RES_MASK);
return err;
}
/*
* We compute the tweak masks twice (both before and after the ECB encryption or
* decryption) to avoid having to allocate a temporary buffer and/or make
* mutliple calls to the 'ecb(..)' instance, which usually would be slower than
* just doing the gf128mul_x_ble() calls again.
*/
static int xor_tweak(struct skcipher_request *req, bool second_pass)
{
struct rctx *rctx = skcipher_request_ctx(req);
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
const int bs = XTS_BLOCK_SIZE;
struct skcipher_walk w;
le128 t = rctx->t;
int err;
if (second_pass) {
req = &rctx->subreq;
/* set to our TFM to enforce correct alignment: */
skcipher_request_set_tfm(req, tfm);
}
err = skcipher_walk_virt(&w, req, false);
while (w.nbytes) {
unsigned int avail = w.nbytes;
le128 *wsrc;
le128 *wdst;
wsrc = w.src.virt.addr;
wdst = w.dst.virt.addr;
do {
le128_xor(wdst++, &t, wsrc++);
gf128mul_x_ble(&t, &t);
} while ((avail -= bs) >= bs);
err = skcipher_walk_done(&w, avail);
}
return err;
}
static int xor_tweak_pre(struct skcipher_request *req)
{
return xor_tweak(req, false);
}
static int xor_tweak_post(struct skcipher_request *req)
{
return xor_tweak(req, true);
}
static void crypt_done(struct crypto_async_request *areq, int err)
{
struct skcipher_request *req = areq->data;
if (!err)
err = xor_tweak_post(req);
skcipher_request_complete(req, err);
}
static void init_crypt(struct skcipher_request *req)
{
struct priv *ctx = crypto_skcipher_ctx(crypto_skcipher_reqtfm(req));
struct rctx *rctx = skcipher_request_ctx(req);
struct skcipher_request *subreq = &rctx->subreq;
skcipher_request_set_tfm(subreq, ctx->child);
skcipher_request_set_callback(subreq, req->base.flags, crypt_done, req);
skcipher_request_set_crypt(subreq, req->dst, req->dst,
req->cryptlen, NULL);
/* calculate first value of T */
crypto_cipher_encrypt_one(ctx->tweak, (u8 *)&rctx->t, req->iv);
}
static int encrypt(struct skcipher_request *req)
{
struct rctx *rctx = skcipher_request_ctx(req);
struct skcipher_request *subreq = &rctx->subreq;
init_crypt(req);
return xor_tweak_pre(req) ?:
crypto_skcipher_encrypt(subreq) ?:
xor_tweak_post(req);
}
static int decrypt(struct skcipher_request *req)
{
struct rctx *rctx = skcipher_request_ctx(req);
struct skcipher_request *subreq = &rctx->subreq;
init_crypt(req);
return xor_tweak_pre(req) ?:
crypto_skcipher_decrypt(subreq) ?:
xor_tweak_post(req);
}
static int init_tfm(struct crypto_skcipher *tfm)
{
struct skcipher_instance *inst = skcipher_alg_instance(tfm);
struct xts_instance_ctx *ictx = skcipher_instance_ctx(inst);
struct priv *ctx = crypto_skcipher_ctx(tfm);
struct crypto_skcipher *child;
struct crypto_cipher *tweak;
child = crypto_spawn_skcipher(&ictx->spawn);
if (IS_ERR(child))
return PTR_ERR(child);
ctx->child = child;
tweak = crypto_alloc_cipher(ictx->name, 0, 0);
if (IS_ERR(tweak)) {
crypto_free_skcipher(ctx->child);
return PTR_ERR(tweak);
}
ctx->tweak = tweak;
crypto_skcipher_set_reqsize(tfm, crypto_skcipher_reqsize(child) +
sizeof(struct rctx));
return 0;
}
static void exit_tfm(struct crypto_skcipher *tfm)
{
struct priv *ctx = crypto_skcipher_ctx(tfm);
crypto_free_skcipher(ctx->child);
crypto_free_cipher(ctx->tweak);
}
static void free(struct skcipher_instance *inst)
{
crypto_drop_skcipher(skcipher_instance_ctx(inst));
kfree(inst);
}
static int create(struct crypto_template *tmpl, struct rtattr **tb)
{
struct skcipher_instance *inst;
struct crypto_attr_type *algt;
struct xts_instance_ctx *ctx;
struct skcipher_alg *alg;
const char *cipher_name;
u32 mask;
int err;
algt = crypto_get_attr_type(tb);
if (IS_ERR(algt))
return PTR_ERR(algt);
if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
return -EINVAL;
cipher_name = crypto_attr_alg_name(tb[1]);
if (IS_ERR(cipher_name))
return PTR_ERR(cipher_name);
inst = kzalloc(sizeof(*inst) + sizeof(*ctx), GFP_KERNEL);
if (!inst)
return -ENOMEM;
ctx = skcipher_instance_ctx(inst);
crypto_set_skcipher_spawn(&ctx->spawn, skcipher_crypto_instance(inst));
mask = crypto_requires_off(algt->type, algt->mask,
CRYPTO_ALG_NEED_FALLBACK |
CRYPTO_ALG_ASYNC);
err = crypto_grab_skcipher(&ctx->spawn, cipher_name, 0, mask);
if (err == -ENOENT) {
err = -ENAMETOOLONG;
if (snprintf(ctx->name, CRYPTO_MAX_ALG_NAME, "ecb(%s)",
cipher_name) >= CRYPTO_MAX_ALG_NAME)
goto err_free_inst;
err = crypto_grab_skcipher(&ctx->spawn, ctx->name, 0, mask);
}
if (err)
goto err_free_inst;
alg = crypto_skcipher_spawn_alg(&ctx->spawn);
err = -EINVAL;
if (alg->base.cra_blocksize != XTS_BLOCK_SIZE)
goto err_drop_spawn;
if (crypto_skcipher_alg_ivsize(alg))
goto err_drop_spawn;
err = crypto_inst_setname(skcipher_crypto_instance(inst), "xts",
&alg->base);
if (err)
goto err_drop_spawn;
err = -EINVAL;
cipher_name = alg->base.cra_name;
/* Alas we screwed up the naming so we have to mangle the
* cipher name.
*/
if (!strncmp(cipher_name, "ecb(", 4)) {
unsigned len;
len = strlcpy(ctx->name, cipher_name + 4, sizeof(ctx->name));
if (len < 2 || len >= sizeof(ctx->name))
goto err_drop_spawn;
if (ctx->name[len - 1] != ')')
goto err_drop_spawn;
ctx->name[len - 1] = 0;
if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
"xts(%s)", ctx->name) >= CRYPTO_MAX_ALG_NAME) {
err = -ENAMETOOLONG;
goto err_drop_spawn;
}
} else
goto err_drop_spawn;
inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
inst->alg.base.cra_priority = alg->base.cra_priority;
inst->alg.base.cra_blocksize = XTS_BLOCK_SIZE;
inst->alg.base.cra_alignmask = alg->base.cra_alignmask |
(__alignof__(u64) - 1);
inst->alg.ivsize = XTS_BLOCK_SIZE;
inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg) * 2;
inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg) * 2;
inst->alg.base.cra_ctxsize = sizeof(struct priv);
inst->alg.init = init_tfm;
inst->alg.exit = exit_tfm;
inst->alg.setkey = setkey;
inst->alg.encrypt = encrypt;
inst->alg.decrypt = decrypt;
inst->free = free;
err = skcipher_register_instance(tmpl, inst);
if (err)
goto err_drop_spawn;
out:
return err;
err_drop_spawn:
crypto_drop_skcipher(&ctx->spawn);
err_free_inst:
kfree(inst);
goto out;
}
static struct crypto_template crypto_tmpl = {
.name = "xts",
.create = create,
.module = THIS_MODULE,
};
static int __init crypto_module_init(void)
{
return crypto_register_template(&crypto_tmpl);
}
static void __exit crypto_module_exit(void)
{
crypto_unregister_template(&crypto_tmpl);
}
module_init(crypto_module_init);
module_exit(crypto_module_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("XTS block cipher mode");
MODULE_ALIAS_CRYPTO("xts");