linux-kernel - Re: [PATCH 2/2] crypto: ccree: enable support for hardware keys

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Date:   Mon, 23 Apr 2018 10:24:43 +0300
From:   Gilad Ben-Yossef <gilad@...yossef.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Ofir Drang <ofir.drang@....com>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] crypto: ccree: enable support for hardware keys

On Thu, Apr 19, 2018 at 6:35 AM, Herbert Xu <herbert@...dor.apana.org.au> wrote:
> On Mon, Apr 09, 2018 at 11:42:31AM +0300, Gilad Ben-Yossef wrote:
>>
>> Please look again. The stub version of cc_is_hw_key() doing that is being
>> replaced in this patch.
>
> The point is that the existing mechanism was unused before and this
> is new code.  So you can't really point to the stubbed-out function
> as a precedent.

hm... I was trying to point to the s390 implementation as a precedent,
not my own stub code.
Sorry if I miscommunicated my intent.

>
>> The s390 key and the cryptocell keys are not the same:
>>
>> Their is, I believe, is an AES key encrypted by some internal key/algorithm.
>>
>> The cryptocell "key" is a token, which is internally comprised of one
>> or two indexes, referencing slots in the internal memory in the
>> hardware, and a key size, that describe the size of the key.
>>
>> I thought it would be confusing to use "paes" to describe both, since
>> they are not interchangeable.
>> You would not be able to feed an paes key that works with the s390
>> version to cryptocell and vice verse and get it work.
>
> Thanks for the info.
>
>> Having said, if you prefer to have "paes" simply designate
>> "implementation specific token for an AES key" I'm perfectly fine with
>> that.
>
> Well by definition none of these hardware keys will be compatible
> with each other so I don't really see the point of using individual
> algorithm names such as paes or haes.  This would make sense only if
> they were somehow compatible with each other.
>
> So instead of using algorithm names, you really want refer to the
> specific driver name, which means that they can all use the same
> algorithm name.

Sounds good to me.

>
>> > As to your patch specifically, there is one issue where you're
>> > directly dereferencing the key as a struct.  This is a no-no because
>> > the key may have come from user-space.  You must treat it as a
>> > binary blob.  The s390 code seems to do this correctly.
>>
>> As noted above, the haes "key" is really a token encoding 3 different
>> pieces of information:
>
> My point is that you should not just cast it but instead do a
> copy to properly aligned kernel memory.


That is a good point I completely missed. Thanks!

A v2 will follow shortly.

Thanks,
Gilad



-- 
Gilad Ben-Yossef
Chief Coffee Drinker

"If you take a class in large-scale robotics, can you end up in a
situation where the homework eats your dog?"
 -- Jean-Baptiste Queru