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