[dm-devel] [PATCH v5] crypto: xts - Drop use of auxiliary buffer
Ondrej Mosnacek
omosnace at redhat.com
Tue Sep 11 07:40:08 UTC 2018
Since commit acb9b159c784 ("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 at redhat.com>
---
crypto/xts.c | 269 +++++++++------------------------------------------
1 file changed, 46 insertions(+), 223 deletions(-)
Changes in v5:
- fix dumb mistakes
v4: https://www.spinics.net/lists/linux-crypto/msg34889.html
Changes in v4:
- small cleanup suggested by Eric Biggers
v3: https://www.spinics.net/lists/linux-crypto/msg34823.html
Changes in v3:
- add comment explaining the new approach as suggested by Eric
- ensure correct alignment in second xor_tweak() pass
- align performance results table header to the right
v2: https://www.spinics.net/lists/linux-crypto/msg34799.html
Changes in v2:
- rebase to latest cryptodev tree
v1: https://www.spinics.net/lists/linux-crypto/msg34776.html
diff --git a/crypto/xts.c b/crypto/xts.c
index ccf55fbb8bc2..847f54f76789 100644
--- a/crypto/xts.c
+++ b/crypto/xts.c
@@ -26,8 +26,6 @@
#include <crypto/b128ops.h>
#include <crypto/gf128mul.h>
-#define XTS_BUFFER_SIZE 128u
-
struct priv {
struct crypto_skcipher *child;
struct crypto_cipher *tweak;
@@ -39,19 +37,7 @@ struct xts_instance_ctx {
};
struct rctx {
- le128 buf[XTS_BUFFER_SIZE / sizeof(le128)];
-
le128 t;
-
- le128 *ext;
-
- struct scatterlist srcbuf[2];
- struct scatterlist dstbuf[2];
- struct scatterlist *src;
- struct scatterlist *dst;
-
- unsigned int left;
-
struct skcipher_request subreq;
};
@@ -96,81 +82,27 @@ static int setkey(struct crypto_skcipher *parent, const u8 *key,
return err;
}
-static int post_crypt(struct skcipher_request *req)
+/*
+ * 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);
- le128 *buf = rctx->ext ?: rctx->buf;
- struct skcipher_request *subreq;
+ struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
const int bs = XTS_BLOCK_SIZE;
struct skcipher_walk w;
- struct scatterlist *sg;
- unsigned offset;
+ le128 t = rctx->t;
int err;
- subreq = &rctx->subreq;
- err = skcipher_walk_virt(&w, subreq, false);
-
- while (w.nbytes) {
- unsigned int avail = w.nbytes;
- le128 *wdst;
-
- wdst = w.dst.virt.addr;
-
- do {
- le128_xor(wdst, buf++, wdst);
- wdst++;
- } while ((avail -= bs) >= bs);
-
- err = skcipher_walk_done(&w, avail);
+ if (second_pass) {
+ req = &rctx->subreq;
+ /* set to our TFM to enforce correct alignment: */
+ skcipher_request_set_tfm(req, tfm);
}
-
- rctx->left -= subreq->cryptlen;
-
- if (err || !rctx->left)
- goto out;
-
- rctx->dst = rctx->dstbuf;
-
- scatterwalk_done(&w.out, 0, 1);
- sg = w.out.sg;
- offset = w.out.offset;
-
- if (rctx->dst != sg) {
- rctx->dst[0] = *sg;
- sg_unmark_end(rctx->dst);
- scatterwalk_crypto_chain(rctx->dst, sg_next(sg), 2);
- }
- rctx->dst[0].length -= offset - sg->offset;
- rctx->dst[0].offset = offset;
-
-out:
- return err;
-}
-
-static int pre_crypt(struct skcipher_request *req)
-{
- struct rctx *rctx = skcipher_request_ctx(req);
- le128 *buf = rctx->ext ?: rctx->buf;
- struct skcipher_request *subreq;
- const int bs = XTS_BLOCK_SIZE;
- struct skcipher_walk w;
- struct scatterlist *sg;
- unsigned cryptlen;
- unsigned offset;
- bool more;
- int err;
-
- subreq = &rctx->subreq;
- cryptlen = subreq->cryptlen;
-
- more = rctx->left > cryptlen;
- if (!more)
- cryptlen = rctx->left;
-
- skcipher_request_set_crypt(subreq, rctx->src, rctx->dst,
- cryptlen, NULL);
-
- err = skcipher_walk_virt(&w, subreq, false);
+ err = skcipher_walk_virt(&w, req, false);
while (w.nbytes) {
unsigned int avail = w.nbytes;
@@ -181,180 +113,71 @@ static int pre_crypt(struct skcipher_request *req)
wdst = w.dst.virt.addr;
do {
- *buf++ = rctx->t;
- le128_xor(wdst++, &rctx->t, wsrc++);
- gf128mul_x_ble(&rctx->t, &rctx->t);
+ le128_xor(wdst++, &t, wsrc++);
+ gf128mul_x_ble(&t, &t);
} while ((avail -= bs) >= bs);
err = skcipher_walk_done(&w, avail);
}
- skcipher_request_set_crypt(subreq, rctx->dst, rctx->dst,
- cryptlen, NULL);
-
- if (err || !more)
- goto out;
-
- rctx->src = rctx->srcbuf;
-
- scatterwalk_done(&w.in, 0, 1);
- sg = w.in.sg;
- offset = w.in.offset;
-
- if (rctx->src != sg) {
- rctx->src[0] = *sg;
- sg_unmark_end(rctx->src);
- scatterwalk_crypto_chain(rctx->src, sg_next(sg), 2);
- }
- rctx->src[0].length -= offset - sg->offset;
- rctx->src[0].offset = offset;
-
-out:
return err;
}
-static int init_crypt(struct skcipher_request *req, crypto_completion_t done)
+static int xor_tweak_pre(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;
- gfp_t gfp;
-
- subreq = &rctx->subreq;
- skcipher_request_set_tfm(subreq, ctx->child);
- skcipher_request_set_callback(subreq, req->base.flags, done, req);
-
- gfp = req->base.flags & CRYPTO_TFM_REQ_MAY_SLEEP ? GFP_KERNEL :
- GFP_ATOMIC;
- rctx->ext = NULL;
-
- subreq->cryptlen = XTS_BUFFER_SIZE;
- if (req->cryptlen > XTS_BUFFER_SIZE) {
- unsigned int n = min(req->cryptlen, (unsigned int)PAGE_SIZE);
-
- rctx->ext = kmalloc(n, gfp);
- if (rctx->ext)
- subreq->cryptlen = n;
- }
-
- rctx->src = req->src;
- rctx->dst = req->dst;
- rctx->left = req->cryptlen;
-
- /* calculate first value of T */
- crypto_cipher_encrypt_one(ctx->tweak, (u8 *)&rctx->t, req->iv);
-
- return 0;
+ return xor_tweak(req, false);
}
-static void exit_crypt(struct skcipher_request *req)
+static int xor_tweak_post(struct skcipher_request *req)
{
- struct rctx *rctx = skcipher_request_ctx(req);
-
- rctx->left = 0;
-
- if (rctx->ext)
- kzfree(rctx->ext);
+ return xor_tweak(req, true);
}
-static int do_encrypt(struct skcipher_request *req, int err)
-{
- struct rctx *rctx = skcipher_request_ctx(req);
- struct skcipher_request *subreq;
-
- subreq = &rctx->subreq;
-
- while (!err && rctx->left) {
- err = pre_crypt(req) ?:
- crypto_skcipher_encrypt(subreq) ?:
- post_crypt(req);
-
- if (err == -EINPROGRESS || err == -EBUSY)
- return err;
- }
-
- exit_crypt(req);
- return err;
-}
-
-static void encrypt_done(struct crypto_async_request *areq, int err)
+static void crypt_done(struct crypto_async_request *areq, int err)
{
struct skcipher_request *req = areq->data;
- struct skcipher_request *subreq;
- struct rctx *rctx;
-
- rctx = skcipher_request_ctx(req);
-
- if (err == -EINPROGRESS) {
- if (rctx->left != req->cryptlen)
- return;
- goto out;
- }
-
- subreq = &rctx->subreq;
- subreq->base.flags &= CRYPTO_TFM_REQ_MAY_BACKLOG;
- err = do_encrypt(req, err ?: post_crypt(req));
- if (rctx->left)
- return;
+ if (!err)
+ err = xor_tweak_post(req);
-out:
skcipher_request_complete(req, err);
}
-static int encrypt(struct skcipher_request *req)
-{
- return do_encrypt(req, init_crypt(req, encrypt_done));
-}
-
-static int do_decrypt(struct skcipher_request *req, int 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;
-
- subreq = &rctx->subreq;
+ struct skcipher_request *subreq = &rctx->subreq;
- while (!err && rctx->left) {
- err = pre_crypt(req) ?:
- crypto_skcipher_decrypt(subreq) ?:
- post_crypt(req);
-
- if (err == -EINPROGRESS || err == -EBUSY)
- return err;
- }
+ 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);
- exit_crypt(req);
- return err;
+ /* calculate first value of T */
+ crypto_cipher_encrypt_one(ctx->tweak, (u8 *)&rctx->t, req->iv);
}
-static void decrypt_done(struct crypto_async_request *areq, int err)
+static int encrypt(struct skcipher_request *req)
{
- struct skcipher_request *req = areq->data;
- struct skcipher_request *subreq;
- struct rctx *rctx;
-
- rctx = skcipher_request_ctx(req);
-
- if (err == -EINPROGRESS) {
- if (rctx->left != req->cryptlen)
- return;
- goto out;
- }
-
- subreq = &rctx->subreq;
- subreq->base.flags &= CRYPTO_TFM_REQ_MAY_BACKLOG;
-
- err = do_decrypt(req, err ?: post_crypt(req));
- if (rctx->left)
- return;
+ struct rctx *rctx = skcipher_request_ctx(req);
+ struct skcipher_request *subreq = &rctx->subreq;
-out:
- skcipher_request_complete(req, err);
+ init_crypt(req);
+ return xor_tweak_pre(req) ?:
+ crypto_skcipher_encrypt(subreq) ?:
+ xor_tweak_post(req);
}
static int decrypt(struct skcipher_request *req)
{
- return do_decrypt(req, init_crypt(req, decrypt_done));
+ 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)
--
2.17.1
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