[dm-devel] [PATCH v3 2/2] crypto: lrw - Do not use auxiliary buffer
Ondrej Mosnacek
omosnace at redhat.com
Wed Sep 12 07:57:57 UTC 2018
On Wed, Sep 12, 2018 at 8:51 AM Eric Biggers <ebiggers at kernel.org> wrote:
> On Tue, Sep 11, 2018 at 09:42:39AM +0200, Ondrej Mosnacek wrote:
> > This patch simplifies the LRW template to recompute the LRW 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 MEASUREMENTS (x86_64)
> > Performed using: https://gitlab.com/omos/linux-crypto-bench
> > Crypto driver used: lrw(ecb-aes-aesni)
> >
> > The results show that the new code has about the same performance as the
> > old code. For 512-byte message it seems to be even slightly faster, but
> > that might be just noise.
> >
> > Before:
> > ALGORITHM KEY (b) DATA (B) TIME ENC (ns) TIME DEC (ns)
> > lrw(aes) 256 64 200 203
> > lrw(aes) 320 64 202 204
> > lrw(aes) 384 64 204 205
> > lrw(aes) 256 512 415 415
> > lrw(aes) 320 512 432 440
> > lrw(aes) 384 512 449 451
> > lrw(aes) 256 4096 1838 1995
> > lrw(aes) 320 4096 2123 1980
> > lrw(aes) 384 4096 2100 2119
> > lrw(aes) 256 16384 7183 6954
> > lrw(aes) 320 16384 7844 7631
> > lrw(aes) 384 16384 8256 8126
> > lrw(aes) 256 32768 14772 14484
> > lrw(aes) 320 32768 15281 15431
> > lrw(aes) 384 32768 16469 16293
> >
> > After:
> > ALGORITHM KEY (b) DATA (B) TIME ENC (ns) TIME DEC (ns)
> > lrw(aes) 256 64 197 196
> > lrw(aes) 320 64 200 197
> > lrw(aes) 384 64 203 199
> > lrw(aes) 256 512 385 380
> > lrw(aes) 320 512 401 395
> > lrw(aes) 384 512 415 415
> > lrw(aes) 256 4096 1869 1846
> > lrw(aes) 320 4096 2080 1981
> > lrw(aes) 384 4096 2160 2109
> > lrw(aes) 256 16384 7077 7127
> > lrw(aes) 320 16384 7807 7766
> > lrw(aes) 384 16384 8108 8357
> > lrw(aes) 256 32768 14111 14454
> > lrw(aes) 320 32768 15268 15082
> > lrw(aes) 384 32768 16581 16250
> >
> > [1] https://lkml.org/lkml/2018/8/23/1315
> >
> > Signed-off-by: Ondrej Mosnacek <omosnace at redhat.com>
> > ---
> > crypto/lrw.c | 280 ++++++++++-----------------------------------------
> > 1 file changed, 51 insertions(+), 229 deletions(-)
> >
> > diff --git a/crypto/lrw.c b/crypto/lrw.c
> > index b4f30b6f16d6..d5d2fba9af59 100644
> > --- a/crypto/lrw.c
> > +++ b/crypto/lrw.c
> > @@ -29,8 +29,6 @@
> > #include <crypto/b128ops.h>
> > #include <crypto/gf128mul.h>
> >
> > -#define LRW_BUFFER_SIZE 128u
> > -
> > #define LRW_BLOCK_SIZE 16
> >
> > struct priv {
> > @@ -56,19 +54,7 @@ struct priv {
> > };
> >
> > struct rctx {
> > - be128 buf[LRW_BUFFER_SIZE / sizeof(be128)];
> > -
> > - be128 t;
> > -
> > - be128 *ext;
> > -
> > - struct scatterlist srcbuf[2];
> > - struct scatterlist dstbuf[2];
> > - struct scatterlist *src;
> > - struct scatterlist *dst;
> > -
> > - unsigned int left;
> > -
> > + be128 t, orig_iv;
> > struct skcipher_request subreq;
> > };
> >
> > @@ -135,86 +121,31 @@ static int next_index(u32 *counter)
> > return res;
> > }
> >
> > -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.
> > + */
>
> next_index(), not gf128mul_x_ble().
Fixed for next revision, thanks.
>
> > +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;
> > + struct skcipher_request *subreq = &rctx->subreq;
> >
> > - subreq = &rctx->subreq;
> > -
> > - while (!err && rctx->left) {
> > - err = pre_crypt(req) ?:
> > - crypto_skcipher_decrypt(subreq) ?:
> > - post_crypt(req);
> > + 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, &rctx->orig_iv);
>
> Can you leave a comment that the 'iv' of 'subreq' is set to 'orig_iv' is set so
> that it's available in xor_tweak_post()? My first thought was that the 'iv'
> should be NULL as this same request is also used for the ECB step.
>
> Or alternatively, you could get the IV directly from 'rctx->orig_iv' in
> xor_tweak(), and only save the incremented IV back to 'walk.iv' on the first
> pass. Then subreq->iv would be left NULL.
Good point, now that we have the explicit first/second pass
distinction this should be quite easy to do and will be also cleaner.
Thanks,
--
Ondrej Mosnacek <omosnace at redhat dot com>
Associate Software Engineer, Security Technologies
Red Hat, Inc.
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