linux-kernel - Re: [PATCH 02/36] lib/crypto: aes: Introduce improved AES library

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Message-ID: <20260106063612.GA2630@sol>
Date: Mon, 5 Jan 2026 22:36:12 -0800
From: Eric Biggers <ebiggers@...nel.org>
To: Qingfang Deng <dqfext@...il.com>
Cc: linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ard Biesheuvel <ardb@...nel.org>,
	"Jason A. Donenfeld" <Jason@...c4.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
	linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
	sparclinux@...r.kernel.org, x86@...nel.org,
	Holger Dengler <dengler@...ux.ibm.com>,
	Harald Freudenberger <freude@...ux.ibm.com>
Subject: Re: [PATCH 02/36] lib/crypto: aes: Introduce improved AES library

On Mon, Jan 05, 2026 at 03:47:12PM +0800, Qingfang Deng wrote:
> On 4 Jan 2026 21:12:35 -0800, Eric Biggers wrote:
> >  extern const u8 crypto_aes_sbox[];
> >  extern const u8 crypto_aes_inv_sbox[];
> > +extern const u32 __cacheline_aligned aes_enc_tab[256];
> > +extern const u32 __cacheline_aligned aes_dec_tab[256];
>  
> __cacheline_aligned puts the array in ".data..cacheline_aligned"
> section. As a const array, it should be in ".rodata" section, so
> ____cacheline_aligned (note the extra underscores) should be used
> instead.
> You can also apply the same to crypto_aes_sbox and crypto_aes_inv_sbox
> while at it.
> 
> Regards,
> Qingfang

Good catch!  So the result is that MMU protection isn't applied to the
const data as intended.

I guess I'll change these to the four-underscore ____cacheline_aligned.

Though, I'm tempted to instead just do __aligned(SMP_CACHE_BYTES), to
stay well away from this footgun.

- Eric