[RFC PATCH 6/7] crypto: x86/polyval: Add PCLMULQDQ accelerated implementation of POLYVAL

[Eric Biggers]

On Mon, Jan 24, 2022 at 07:44:21PM -0600, Nathan Huckleberry wrote:
> Add hardware accelerated version of POLYVAL for x86-64 CPUs with
> PCLMULQDQ support.
> 
> This implementation is accelerated using PCLMULQDQ instructions to
> perform the finite field computations.  For added efficiency, 8 blocks
> of the plaintext are processed simultaneously by precomputing the first
> 8 powers of the key.
> 
> Schoolbook multiplication is used instead of Karatsuba multiplication
> because it was found to be slightly faster on x86-64 machines.
> Montgomery reduction must be used instead of Barrett reduction due to
> the difference in modulus between POLYVAL's field and other finite
> fields.
> 
> More information on POLYVAL can be found in the HCTR2 paper:
> Length-preserving encryption with HCTR2:
> https://eprint.iacr.org/2021/1441.pdf
> 
> Signed-off-by: Nathan Huckleberry <nhuck at google.com>
> ---
>  arch/x86/crypto/Makefile                     |   3 +
>  arch/x86/crypto/polyval-clmulni-intel_asm.S  | 319 +++++++++++++++++++

This file is causing a build-time warning:

	arch/x86/crypto/polyval-clmulni-intel_asm.o: warning: objtool: .text+0x0: unreachable instruction

- Eric