linux-kernel - Re: [PATCH 1/1] crypto: testmgr - call shash

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Date:   Mon, 1 Apr 2019 10:30:57 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Lionel Debieve <lionel.debieve@...com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        linux-crypto@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Benjamin Gaignard <benjamin.gaignard@...com>,
        Fabien Dessenne <fabien.dessenne@...com>,
        Ludovic Barre <ludovic.barre@...com>,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH 1/1] crypto: testmgr - call shash_init in crc32c algo

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@...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