crypto: arm64/sm4-gcm - Fix possible crash in GCM cryption

An often overlooked aspect of the skcipher walker API is that an
error is not just indicated by a non-zero return value, but by the
fact that walk->nbytes is zero.

Thus it is an error to call skcipher_walk_done after getting back
walk->nbytes == 0 from the previous interaction with the walker.

This is because when walk->nbytes is zero the walker is left in
an undefined state and any further calls to it may try to free
uninitialised stack memory.

The sm4 arm64 ccm code gets this wrong and ends up calling
skcipher_walk_done even when walk->nbytes is zero.

This patch rewrites the loop in a form that resembles other callers.

Reported-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Fixes: ae1b83c7d572 ("crypto: arm64/sm4 - add CE implementation for GCM mode")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto: arm64 - Fix unused variable compilation warnings of cpu_feature

The cpu feature defined by MODULE_DEVICE_TABLE is only referenced when
compiling as a module, and the warning of unused variable will be
encountered when compiling with intree. The warning can be removed by
adding the __maybe_unused flag.

Fixes: 03c9a333fef1 ("crypto: arm64/ghash - add NEON accelerated fallback for 64-bit PMULL")
Fixes: ae1b83c7d572 ("crypto: arm64/sm4 - add CE implementation for GCM mode")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto: arm64/sm4 - add CE implementation for GCM mode

This patch is a CE-optimized assembly implementation for GCM mode.

Benchmark on T-Head Yitian-710 2.75 GHz, the data comes from the 224 and 224
modes of tcrypt, and compared the performance before and after this patch (the
driver used before this patch is gcm_base(ctr-sm4-ce,ghash-generic)).
The abscissas are blocks of different lengths. The data is tabulated and the
unit is Mb/s:

Before (gcm_base(ctr-sm4-ce,ghash-generic)):

gcm(sm4) | 16 64 256 512 1024 1420 4096 8192
-------------+---------------------------------------------------------------------
GCM enc | 25.24 64.65 104.66 116.69 123.81 125.12 129.67 130.62
GCM dec | 25.40 64.80 104.74 116.70 123.81 125.21 129.68 130.59
GCM mb enc | 24.95 64.06 104.20 116.38 123.55 124.97 129.63 130.61
GCM mb dec | 24.92 64.00 104.13 116.34 123.55 124.98 129.56 130.48

After:

gcm-sm4-ce | 16 64 256 512 1024 1420 4096 8192
-------------+---------------------------------------------------------------------
GCM enc | 108.62 397.18 971.60 1283.92 1522.77 1513.39 1777.00 1806.96
GCM dec | 116.36 398.14 1004.27 1319.11 1624.21 1635.43 1932.54 1974.20
GCM mb enc | 107.13 391.79 962.05 1274.94 1514.76 1508.57 1769.07 1801.58
GCM mb dec | 113.40 389.36 988.51 1307.68 1619.10 1631.55 1931.70 1970.86

Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>