Assign crypto aliases to different AES implementation modules

Assign crypto aliases to different AES implementation modules

The kernel modules aes-neon-blk and aes-neon-bs perform poorly, at least on
Cortex-A72 without crypto extensions. In fact, aes-arm64 outperforms them
on benchmarks, despite it being a simpler implementation (only accelerating
the single-block AES cipher).

For modes of operation where multiple cipher blocks can be processed in
parallel, aes-neon-bs outperforms aes-neon-blk by around 60-70% and aes-arm64
is another 10-20% faster still. But the difference is even more marked with
modes of operation with dependencies between neighbouring blocks, such as
CBC encryption, which defeat parallelism: in these cases, aes-arm64 is
typically around 250% faster than either aes-neon-blk or aes-neon-bs.

The key trade-off with aes-arm64 is that the look-up tables are situated in
RAM. This leaves them potentially open to cache timing attacks. The two other
modules, by contrast, load the look-up tables into NEON registers and so are
able to perform in constant time.

This patch aims to load aes-arm64 more often.

If none of the currently-loaded crypto modules implement a given algorithm,
a new one is typically selected for loading using a platform-neutral alias
describing the required algorithm. To enable users to still
load aes-neon-blk or aes-neon-bs if they really want them, while still
ensuring that aes-arm64 is usually selected, remove the aliases from
aes-neonbs-glue.c and aes-glue.c and apply them to aes-cipher-glue.c, but
still build the two NEON modules.

Since aes-glue.c can also be used to build aes-ce-blk, leave them enabled
if USE_V8_CRYPTO_EXTENSIONS is defined, to ensure they are selected if we
in future use a CPU which has the crypto extensions enabled.

Note that the algorithm priority specifiers are unchanged, so if
aes-neon-bs is loaded at the same time as aes-arm64, the former will be
used in preference. However, aes-neon-blk and aes-arm64 have tied priority,
so whichever module was loaded first will be used (assuming aes-neon-bs is
not loaded).

Signed-off-by: Ben Avison <bavison@riscosopen.org>