For the final round, avoid the expanded and padded lookup tables
exported by the generic AES driver. Instead, for encryption, we can
perform byte loads from the same table we used for the inner rounds,
which will still be hot in the caches. For decryption, use the inverse
AES Sbox directly, which is 4x smaller than the inverse lookup table
exported by the generic driver.
This should significantly reduce the Dcache footprint of our code,
which makes the code more robust against timing attacks. It does not
introduce any additional module dependencies, given that we already
rely on the core AES module for the shared key expansion routines.
It also frees up register x18, which is not available as a scratch
register on all platforms, which and so avoiding it improves
shareability of this code.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Shuffle some instructions around in the __hround macro to shave off
0.1 cycles per byte on Cortex-A57.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Using simple adrp/add pairs to refer to the AES lookup tables exposed by
the generic AES driver (which could be loaded far away from this driver
when KASLR is in effect) was unreliable at module load time before commit
41c066f2c4 ("arm64: assembler: make adr_l work in modules under KASLR"),
which is why the AES code used literals instead.
So now we can get rid of the literals, and switch to the adr_l macro.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This adds a scalar implementation of AES, based on the precomputed tables
that are exposed by the generic AES code. Since rotates are cheap on arm64,
this implementation only uses the 4 core tables (of 1 KB each), and avoids
the prerotated ones, reducing the D-cache footprint by 75%.
On Cortex-A57, this code manages 13.0 cycles per byte, which is ~34% faster
than the generic C code. (Note that this is still >13x slower than the code
that uses the optional ARMv8 Crypto Extensions, which manages <1 cycles per
byte.)
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Ard Biesheuvel