Hi Herbert, Mikulas,
I noticed the discussion about using kmalloc() inside crypto code and it
made me wonder if the code in xts.c can actually be simplified to not
require kmalloc() at all, while not badly affecting performace. I played
around with it a little and it turns out we can drop the whole caching
of tweak blocks, reducing code size by ~200 lines and not only preserve,
but even improve the performance in some cases. See the full patch
below.
Obviously, this doesn't solve the general issue of using kmalloc() in
crypto API routines, but it does resolve the original reported problem
and also makes the XTS code easier to maintain.
Regards,
Ondrej
----->8-----
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
Cc: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
---
crypto/xts.c | 258 ++++++---------------------------------------------
1 file changed, 30 insertions(+), 228 deletions(-)
diff --git a/crypto/xts.c b/crypto/xts.c
index 12284183bd20..6c49e76df8ca 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;
};
@@ -96,265 +82,81 @@ static int setkey(struct crypto_skcipher *parent, const u8 *key,
return err;
}
-static int post_crypt(struct skcipher_request *req)
+static int xor_tweak(struct rctx *rctx, 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 offset;
+ le128 t = rctx->t;
int err;
- subreq = &rctx->subreq;
- err = skcipher_walk_virt(&w, subreq, false);
+ 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, buf++, wdst);
- wdst++;
+ le128_xor(wdst++, &t, wsrc++);
+ gf128mul_x_ble(&t, &t);
} while ((avail -= bs) >= bs);
err = skcipher_walk_done(&w, avail);
}
- 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), 0, 2);
- }
- rctx->dst[0].length -= offset - sg->offset;
- rctx->dst[0].offset = offset;
-
-out:
return err;
}
-static int pre_crypt(struct skcipher_request *req)
+static void crypt_done(struct crypto_async_request *areq, int err)
{
+ struct skcipher_request *req = areq->data;
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);
-
- while (w.nbytes) {
- unsigned int avail = w.nbytes;
- le128 *wsrc;
- le128 *wdst;
-
- wsrc = w.src.virt.addr;
- wdst = w.dst.virt.addr;
-
- do {
- *buf++ = rctx->t;
- le128_xor(wdst++, &rctx->t, wsrc++);
- gf128mul_x_ble(&rctx->t, &rctx->t);
- } while ((avail -= bs) >= bs);
-
- err = skcipher_walk_done(&w, avail);
- }
-
- skcipher_request_set_crypt(subreq, rctx->dst, rctx->dst,
- cryptlen, NULL);
+ struct skcipher_request *subreq = &rctx->subreq;
- if (err || !more)
- goto out;
+ if (!err)
+ err = xor_tweak(rctx, subreq);
- 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), 0, 2);
- }
- rctx->src[0].length -= offset - sg->offset;
- rctx->src[0].offset = offset;
-
-out:
- return err;
+ skcipher_request_complete(req, err);
}
-static int init_crypt(struct skcipher_request *req, crypto_completion_t done)
+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;
- gfp_t gfp;
+ struct skcipher_request *subreq = &rctx->subreq;
- 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;
+ 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);
-
- return 0;
-}
-
-static void exit_crypt(struct skcipher_request *req)
-{
- struct rctx *rctx = skcipher_request_ctx(req);
-
- rctx->left = 0;
-
- if (rctx->ext)
- kzfree(rctx->ext);
-}
-
-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)
-{
- 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;
-
-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)
{
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;
- }
-
- exit_crypt(req);
- return err;
-}
-
-static void decrypt_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_decrypt(req, err ?: post_crypt(req));
- if (rctx->left)
- return;
-
-out:
- skcipher_request_complete(req, err);
+ init_crypt(req);
+ return xor_tweak(rctx, req) ?:
+ crypto_skcipher_encrypt(subreq) ?:
+ xor_tweak(rctx, subreq);
}
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(rctx, req) ?:
+ crypto_skcipher_decrypt(subreq) ?:
+ xor_tweak(rctx, subreq);
}
static int init_tfm(struct crypto_skcipher *tfm)
--
2.17.1
--
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