Re: [PATCH] crypto: lib/Kconfig - Select and hide arch options

[Eric Biggers <ebiggers@kernel.org>]

On Wed, Feb 26, 2025 at 12:36:33PM +0800, Herbert Xu wrote:
> The ARCH_MAY_HAVE patch missed arm64, mips and s390.  But it may
> also lead to arch options being enabled but ineffective because
> of modular/built-in conflicts.
> 
> As the primary user of all these options wireguard is selecting
> the arch options anyway, make the same selections at the lib/crypto
> option level and hide the arch options from the user.
> 
> Fixes: 1047e21aecdf ("crypto: lib/Kconfig - Fix lib built-in failure when arch is modular")
> Reported-by: kernel test robot <lkp@intel.com>
> Reported-by: Arnd Bergmann <arnd@kernel.org>
> Closes: https://lore.kernel.org/oe-kbuild-all/202502232152.JC84YDLp-lkp@intel.com/
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

As I said earlier, fixing the arch-optimized code to be enabled automatically is
the right way to do it.  There are still some issues with this patch, though:

>  config CRYPTO_LIB_CHACHA
>  	tristate "ChaCha library interface"
> +	select CRYPTO
>  	select CRYPTO_LIB_CHACHA_GENERIC if CRYPTO_ARCH_HAVE_LIB_CHACHA=n
> +	select CRYPTO_CHACHA20_X86_64 if X86 && 64BIT
> +	select CRYPTO_CHACHA20_NEON if ARM || (ARM64 && KERNEL_MODE_NEON)
> +	select CRYPTO_CHACHA_MIPS if CPU_MIPS32_R2
> +	select CRYPTO_CHACHA_S390 if S390
> +	select CRYPTO_CHACHA20_P10 if PPC64 && CPU_LITTLE_ENDIAN && VSX

There's no need to have a select for every architecture, with the dependencies
redundantly listed.  Instead just 'default' each of the arch-optimized options
to CRYPTO_LIB_CHACHA.

> config CRYPTO_CHACHA20_X86_64
>	tristate
>	depends on X86 && 64BIT
>	default CRYPTO_CHACHA20
>	select CRYPTO_ARCH_HAVE_LIB_CHACHA
[...]
>
> config CRYPTO_CHACHA20
> 	tristate "ChaCha"
> 	select CRYPTO_LIB_CHACHA_GENERIC
> 	select CRYPTO_SKCIPHER

This introduces a problem where to enable optimized ChaCha in the crypto API
users will now need to enable CRYPTO_LIB_CHACHA, instead of
CRYPTO_CHACHA20_X86_64 etc. as was needed before.  LIB symbols should never be
user-selectable, so that makes no sense.

The way it should work is that CRYPTO_CHACHA20 should just select
CRYPTO_LIB_CHACHA (and thus also the optimized code).

And similarly for the other algorithms, which should be in their patches.

- Eric