Re: [PATCH 1/1] crypto: testmgr - call shash_init in crc32c algo

From: Eric Biggers <ebiggers@kernel.org>
To: Lionel Debieve <lionel.debieve@st.com>
Cc: Benjamin Gaignard <benjamin.gaignard@st.com>,
	Alexandre Torgue <alexandre.torgue@st.com>,
	linux-kernel@vger.kernel.org,
	Fabien Dessenne <fabien.dessenne@st.com>,
	linux-stm32@st-md-mailman.stormreply.com,
	linux-crypto@vger.kernel.org,
	Maxime Coquelin <mcoquelin.stm32@gmail.com>,
	Ludovic Barre <ludovic.barre@st.com>,
	"David S . Miller" <davem@davemloft.net>,
	linux-arm-kernel@lists.infradead.org,
	Herbert Xu <herbert@gondor.apana.org.au>
Subject: Re: [PATCH 1/1] crypto: testmgr - call shash_init in crc32c algo
Date: Mon, 1 Apr 2019 10:30:57 -0700	[thread overview]
Message-ID: <20190401173056.GD131675@gmail.com> (raw)
In-Reply-To: <1554123264-24243-1-git-send-email-lionel.debieve@st.com>

Hi Lionel,

On Mon, Apr 01, 2019 at 02:54:24PM +0200, Lionel Debieve wrote:
> In case of device call required in low level driver,
> the context must be initialized before calling the final
> function.
> 
> Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
> ---
>  crypto/testmgr.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/crypto/testmgr.c b/crypto/testmgr.c
> index 8386038..4a00d7c 100644
> --- a/crypto/testmgr.c
> +++ b/crypto/testmgr.c
> @@ -2181,6 +2181,13 @@ static int alg_test_crc32c(const struct alg_test_desc *desc,
>  		shash->tfm = tfm;
>  		shash->flags = 0;
>  
> +		err = crypto_shash_init(shash);
> +		if (err) {
> +			printk(KERN_ERR "alg: crc32c: init failed for "
> +			       "%s: %d\n", driver, err);
> +			break;
> +		}
> +
>  		*ctx = 420553207;
>  		err = crypto_shash_final(shash, (u8 *)&val);
>  		if (err) {
> -- 
> 2.7.4
> 

This defeats the point of the test, which is that crc32c implementations are
expected to use the same shash_desc context format and be usable by calling
crypto_shash_update() directly after initializing the context manually, without
a prior crypto_shash_init().  See for example ext4_chksum() in fs/ext4/ext4.h:

	static inline u32 ext4_chksum(struct ext4_sb_info *sbi, u32 crc,
				      const void *address, unsigned int length)
	{
		struct {
			struct shash_desc shash;
			char ctx[4];
		} desc;

		BUG_ON(crypto_shash_descsize(sbi->s_chksum_driver)!=sizeof(desc.ctx));

		desc.shash.tfm = sbi->s_chksum_driver;
		desc.shash.flags = 0;
		*(u32 *)desc.ctx = crc;

		BUG_ON(crypto_shash_update(&desc.shash, address, length));

		return *(u32 *)desc.ctx;
	}

I think you need to fix the stm32 crc32 driver to not store anything extra in
the shash_desc context, and only use hardware during ->update().

- Eric

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