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Subject: Re: [PATCH] selftests/sgx: fix EINIT failure dueto
 SGX_INVALID_SIGNATURE
To:     Jarkko Sakkinen <jarkko@kernel.org>,
        Jia Zhang <zhang.jia@linux.alibaba.com>
Cc:     Andy Lutomirski <luto@amacapital.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Sean Christopherson <seanjc@google.com>,
        Shuah Khan <shuah@kernel.org>, X86 ML <x86@kernel.org>,
        linux-sgx@vger.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
References: <20210301051836.30738-1-tianjia.zhang@linux.alibaba.com>
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 <20ef1254-007d-04ce-8df5-5122ffd4d8d3@linux.alibaba.com>
 <YEmRlQ8vL2inziEK@kernel.org>
From:   Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Message-ID: <710b65d6-e492-ae24-f2af-6973e1df1b85@linux.alibaba.com>
Date:   Thu, 11 Mar 2021 12:53:49 +0800
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On 3/11/21 11:42 AM, Jarkko Sakkinen wrote:
> On Thu, Mar 11, 2021 at 10:47:50AM +0800, Jia Zhang wrote:
>>
>>
>> On 2021/3/11 上午5:39, Jarkko Sakkinen wrote:
>>> On Wed, Mar 10, 2021 at 08:44:44PM +0800, Jia Zhang wrote:
>>>>
>>>>
>>>> On 2021/3/2 下午9:47, Jarkko Sakkinen wrote:
>>>>> On Mon, Mar 01, 2021 at 09:54:37PM -0800, Andy Lutomirski wrote:
>>>>>> On Mon, Mar 1, 2021 at 9:06 PM Tianjia Zhang
>>>>>> <tianjia.zhang@linux.alibaba.com> wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On 3/1/21 5:54 PM, Jarkko Sakkinen wrote:
>>>>>>>> On Mon, Mar 01, 2021 at 01:18:36PM +0800, Tianjia Zhang wrote:
>>>>>>>>> q2 is not always 384-byte length. Sometimes it only has 383-byte.
>>>>>>>>
>>>>>>>> What does determine this?
>>>>>>>>
>>>>>>>>> In this case, the valid portion of q2 is reordered reversely for
>>>>>>>>> little endian order, and the remaining portion is filled with zero.
>>>>>>>>
>>>>>>>> I'm presuming that you want to say "In this case, q2 needs to be reversed because...".
>>>>>>>>
>>>>>>>> I'm lacking these details:
>>>>>>>>
>>>>>>>> 1. Why the length of Q2 can vary?
>>>>>>>> 2. Why reversing the bytes is the correct measure to counter-measure
>>>>>>>>      this variation?
>>>>>>>>
>>>>>>>> /Jarkko
>>>>>>>>
>>>>>>>
>>>>>>> When use openssl to generate a key instead of using the built-in
>>>>>>> sign_key.pem, there is a probability that will encounter this problem.
>>>>>>>
>>>>>>> Here is a problematic key I encountered. The calculated q1 and q2 of
>>>>>>> this key are both 383 bytes, If the length is not processed, the
>>>>>>> hardware signature will fail.
>>>>>>
>>>>>> Presumably the issue is that some keys have parameters that have
>>>>>> enough leading 0 bits to be effectively shorter.  The openssl API
>>>>>> (and, sadly, a bunch  of the ASN.1 stuff) treats these parameters as
>>>>>> variable-size integers.
>>>>>
>>>>> But the test uses a static key. It used to generate a key on fly but
>>>>
>>>> IMO even though the test code, it comes from the linux kernel, meaning
>>>> that its quality has a certain guarantee and it is a good reference, so
>>>> the test code still needs to ensure its correctness.
>>>
>>> Hmm... what is working incorrectly then?
>>
>> In current implementation, it is working well, after all the static key
>> can derive the full 384-byte length of q1 and q2. As mentioned above, if
>> someone refers to the design of signing tool from selftest code, it is
>> quite possible that the actual implementation will use dynamical or
>> external signing key deriving shorter q1 and/or q2 in length.
> 
> A self-test needs is not meant to be generic to be directly used in 3rd
> party code. With the current key there is not issue => there is no issue.
> 

For keys generated on fly, self-test does not work properly, this 
experience is really worse.

Best regards,
Tianjia