linux-kernel - Re: [PATCH 0/9] Remove per-architecture ChaCha skcipher glue code

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Message-ID: <Z_Nimiv1Wkfo3gBd@gondor.apana.org.au>
Date: Mon, 7 Apr 2025 13:28:58 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Eric Biggers <ebiggers@...nel.org>
Cc: linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
	linux-s390@...r.kernel.org, x86@...nel.org, ardb@...nel.org,
	Jason@...c4.com, torvalds@...ux-foundation.org
Subject: Re: [PATCH 0/9] Remove per-architecture ChaCha skcipher glue code

Eric Biggers <ebiggers@...nel.org> wrote:
> Currently each architecture exposes ChaCha not only through the library
> API, but also through the crypto_skcipher API.  That requires each
> architecture to implement essentially the same skcipher glue code.
> 
> Following the example of what's been done for crc32 and crc32c,
> eliminate this redundancy by making crypto/chacha.c register both the
> generic and architecture-optimized skcipher algorithms, implemented on
> top of the appropriate library functions.  This removes almost 800 lines
> of code and disentangles the library code from the skcipher API.
> 
> From what I remember, the following are the reasons why it wasn't just
> done this way originally.  But none of these really hold water:
> 
> - The skcipher code was there first, so it may have seemed more natural
>  to add onto it rather than replace it.
> 
> - Architectures could register multiple skcipher algorithms using
>  different CPU features and have them all be tested in a single boot.
>  This was convenient in theory, but it never really worked properly.
>  It didn't apply to the library code, the x86 ChaCha code wasn't
>  actually doing this (it used static keys instead), and this cannot
>  catch bugs like accidentally using an AVX instruction in SSE code.
>  Instead, a correct solution, which also doesn't require any special
>  kernel support, is to just boot the kernel in QEMU using different
>  -cpu arguments as needed to test all the code.
> 
> - There was a concern about changing cra_driver_names potentially
>  breaking users.  But in practice users rely on cra_name, not
>  cra_driver_name.  We already change, add, and remove cra_driver_names
>  occasionally for various reasons.  And even if someone was relying on
>  a specific cra_driver_name, there are some more lightweight
>  compatibility tricks that could be used.
> 
> - There was a desire for users to be able to override the kernel's
>  choice of ChaCha implementation by blacklisting the arch-optimized
>  ChaCha module.  But that already became mostly impossible when the
>  library functions were added to the same module.  And in practice
>  users don't do this anyway.  Even if, hypothetically, someone really
>  needed to do this and for some reason the kernel couldn't be fixed to
>  make the right choice in their case automatically, there are other
>  ways this could be implemented such as a module parameter.
> 
> Eric Biggers (9):
>  crypto: riscv/chacha - implement library instead of skcipher
>  crypto: chacha - centralize the skcipher wrappers for arch code
>  crypto: arm/chacha - remove the redundant skcipher algorithms
>  crypto: arm64/chacha - remove the skcipher algorithms
>  crypto: mips/chacha - remove the skcipher algorithms
>  crypto: powerpc/chacha - remove the skcipher algorithms
>  crypto: s390/chacha - remove the skcipher algorithms
>  crypto: x86/chacha - remove the skcipher algorithms
>  crypto: chacha - remove <crypto/internal/chacha.h>
> 
> arch/arm/crypto/Kconfig                 |   7 -
> arch/arm/crypto/chacha-glue.c           | 243 +---------------------
> arch/arm/crypto/chacha-neon-core.S      |   2 +-
> arch/arm64/crypto/Kconfig               |   7 -
> arch/arm64/crypto/chacha-neon-core.S    |   2 +-
> arch/arm64/crypto/chacha-neon-glue.c    | 146 +------------
> arch/mips/crypto/Kconfig                |   6 -
> arch/mips/crypto/chacha-glue.c          | 131 +-----------
> arch/powerpc/crypto/Kconfig             |   8 -
> arch/powerpc/crypto/chacha-p10-glue.c   | 147 +-------------
> arch/riscv/crypto/Kconfig               |  11 +-
> arch/riscv/crypto/chacha-riscv64-glue.c | 112 ++++------
> arch/riscv/crypto/chacha-riscv64-zvkb.S |  71 +++----
> arch/s390/crypto/Kconfig                |   7 -
> arch/s390/crypto/chacha-glue.c          |  99 ++-------
> arch/x86/crypto/Kconfig                 |   9 -
> arch/x86/crypto/chacha_glue.c           | 144 +------------
> crypto/Makefile                         |   3 +-
> crypto/chacha.c                         | 260 ++++++++++++++++++++++++
> crypto/chacha_generic.c                 | 139 -------------
> include/crypto/chacha.h                 |   9 +
> include/crypto/internal/chacha.h        |  43 ----
> 22 files changed, 413 insertions(+), 1193 deletions(-)
> create mode 100644 crypto/chacha.c
> delete mode 100644 crypto/chacha_generic.c
> delete mode 100644 include/crypto/internal/chacha.h
> 
> base-commit: 56f944529ec2292cbe63377a76df3759d702dd39

All applied.  Thanks.
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt