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Subject: Re: [PATCH v2 05/13] crypto: simd - Update `walksize` in simd
 skcipher
From:   Jerry Shih <jerry.shih@sifive.com>
In-Reply-To: <20231128035814.GH1463@sol.localdomain>
Date:   Tue, 28 Nov 2023 13:38:29 +0800
Cc:     Paul Walmsley <paul.walmsley@sifive.com>, palmer@dabbelt.com,
        Albert Ou <aou@eecs.berkeley.edu>, herbert@gondor.apana.org.au,
        davem@davemloft.net, conor.dooley@microchip.com, ardb@kernel.org,
        heiko@sntech.de, phoebe.chen@sifive.com, hongrong.hsu@sifive.com,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-crypto@vger.kernel.org
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References: <20231127070703.1697-1-jerry.shih@sifive.com>
 <20231127070703.1697-6-jerry.shih@sifive.com>
 <20231128035814.GH1463@sol.localdomain>
To:     Eric Biggers <ebiggers@kernel.org>
Precedence: bulk

On Nov 28, 2023, at 11:58, Eric Biggers <ebiggers@kernel.org> wrote:
> On Mon, Nov 27, 2023 at 03:06:55PM +0800, Jerry Shih wrote:
>> The `walksize` assignment is missed in simd skcipher.
>>=20
>> Signed-off-by: Jerry Shih <jerry.shih@sifive.com>
>> ---
>> crypto/cryptd.c | 1 +
>> crypto/simd.c   | 1 +
>> 2 files changed, 2 insertions(+)
>>=20
>> diff --git a/crypto/cryptd.c b/crypto/cryptd.c
>> index bbcc368b6a55..253d13504ccb 100644
>> --- a/crypto/cryptd.c
>> +++ b/crypto/cryptd.c
>> @@ -405,6 +405,7 @@ static int cryptd_create_skcipher(struct =
crypto_template *tmpl,
>> 		(alg->base.cra_flags & CRYPTO_ALG_INTERNAL);
>> 	inst->alg.ivsize =3D crypto_skcipher_alg_ivsize(alg);
>> 	inst->alg.chunksize =3D crypto_skcipher_alg_chunksize(alg);
>> +	inst->alg.walksize =3D crypto_skcipher_alg_walksize(alg);
>> 	inst->alg.min_keysize =3D crypto_skcipher_alg_min_keysize(alg);
>> 	inst->alg.max_keysize =3D crypto_skcipher_alg_max_keysize(alg);
>>=20
>> diff --git a/crypto/simd.c b/crypto/simd.c
>> index edaa479a1ec5..ea0caabf90f1 100644
>> --- a/crypto/simd.c
>> +++ b/crypto/simd.c
>> @@ -181,6 +181,7 @@ struct simd_skcipher_alg =
*simd_skcipher_create_compat(const char *algname,
>>=20
>> 	alg->ivsize =3D ialg->ivsize;
>> 	alg->chunksize =3D ialg->chunksize;
>> +	alg->walksize =3D ialg->walksize;
>> 	alg->min_keysize =3D ialg->min_keysize;
>> 	alg->max_keysize =3D ialg->max_keysize;
>=20
> What are the consequences of this bug?  I wonder if it actually =
matters?  The
> "inner" algorithm is the one that actually gets used for the "walk", =
right?
>=20
> - Eric

Without this, we might still use chunksize or cra_blocksize as the =
walksize
even though we setup with the larger walksize.

Here is the code for the walksize default value:
	static int skcipher_prepare_alg(struct skcipher_alg *alg)
	{
		...
		if (!alg->chunksize)
			alg->chunksize =3D base->cra_blocksize;
		if (!alg->walksize)
			alg->walksize =3D alg->chunksize;

And we already have the bigger walksize for x86 aes-xts.
		.base =3D {
			.cra_name		=3D "__xts(aes)",
			...
		},
		.walksize	=3D 2 * AES_BLOCK_SIZE,

The x86 aes-xts only uses one `walk` to handle the tail elements. It =
assumes
that the walksize contains 2 aes blocks. If walksize is not set =
correctly, maybe
some tail elements is not processed in simd-cipher mode for x86 aes-xts.

-Jerry=