linux-kernel - Re: [PATCH v2 04/20] crypto: aegis128-neon - Move to more abstract 'ksimd' guard API

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Message-ID: <202510020918.7E358227@keescook>
Date: Thu, 2 Oct 2025 09:20:10 -0700
From: Kees Cook <kees@...nel.org>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, herbert@...dor.apana.org.au,
	linux@...linux.org.uk, Ard Biesheuvel <ardb@...nel.org>,
	Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Mark Brown <broonie@...nel.org>, Eric Biggers <ebiggers@...nel.org>
Subject: Re: [PATCH v2 04/20] crypto: aegis128-neon - Move to more abstract
 'ksimd' guard API

On Wed, Oct 01, 2025 at 11:02:06PM +0200, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
> 
> Move away from calling kernel_neon_begin() and kernel_neon_end()
> directly, and instead, use the newly introduced scoped_ksimd() API. This
> permits arm64 to modify the kernel mode NEON API without affecting code
> that is shared between ARM and arm64.
> 
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> ---
>  crypto/aegis128-neon.c | 33 +++++++-------------
>  1 file changed, 12 insertions(+), 21 deletions(-)
> 
> diff --git a/crypto/aegis128-neon.c b/crypto/aegis128-neon.c
> index 9ee50549e823..b41807e63bd3 100644
> --- a/crypto/aegis128-neon.c
> +++ b/crypto/aegis128-neon.c
> @@ -4,7 +4,7 @@
>   */
>  
>  #include <asm/cpufeature.h>
> -#include <asm/neon.h>
> +#include <asm/simd.h>
>  
>  #include "aegis.h"
>  #include "aegis-neon.h"
> @@ -24,32 +24,28 @@ void crypto_aegis128_init_simd(struct aegis_state *state,
>  			       const union aegis_block *key,
>  			       const u8 *iv)
>  {
> -	kernel_neon_begin();
> -	crypto_aegis128_init_neon(state, key, iv);
> -	kernel_neon_end();
> +	scoped_ksimd()
> +		crypto_aegis128_init_neon(state, key, iv);
>  }

For these cases (to avoid the indentation change), do you want to use
just "guard" instead of "scope_guard", or do you want to explicitly
require explicit scope context even when the scope ends at the function
return?

-- 
Kees Cook