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From: Jarkko Sakkinen <jarkko@kernel.org>
To: Jia Zhang <zhang.jia@linux.alibaba.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
	Tianjia Zhang <tianjia.zhang@linux.alibaba.com>,
	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>
Subject: Re: [PATCH] selftests/sgx: fix EINIT failure dueto SGX_INVALID_SIGNATURE
Date: Thu, 11 Mar 2021 05:42:13 +0200	[thread overview]
Message-ID: <YEmRlQ8vL2inziEK@kernel.org> (raw)
In-Reply-To: <20ef1254-007d-04ce-8df5-5122ffd4d8d3@linux.alibaba.com>

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.

> 
> Going back the technical background, I'm not a crypto expert, so I
> choose to check the code, doc and make experiment.
> 
> Accorindg to intel sdm vol3 37.14:
> 
> ```
> SIGSTRUCT includes four 3072-bit integers (MODULUS, SIGNATURE, Q1, Q2).
> Each such integer is represented as a byte strings of length 384, with
> the most significant byte at the position “offset + 383”, and the least
> significant byte at position “offset”.
> 
> ...
> 
> The 3072-bit integers Q1 and Q2 are defined by:
> q1 = floor(Signature^2 / Modulus);
> q2 = floor((Signature^3 - q1 * Signature * Modulus) / Modulus);
> ```
> 
> and the implementation of singing tool from Intel SGX SDK
> (https://github.com/intel/linux-sgx/blob/master/sdk/sign_tool/SignTool/sign_tool.cpp#L381
> ), the most significant byte shuld be at the position “offset +
> q1/q2_actuall_len”, and the padding portion should be filled with zero,
> and don't involve the order reverse, but the selftest code always does.
> This is the root cause of SGX_INVALID_SIGNATURE.
> 
> Just simplily enforce size_q1 and size_q2 to SE_KEY_SIZE, and generate
> randome siging key with `openssl genrsa -3 -out signing_key.pem 3072`,
> the SGX_INVALID_SIGNATURE error will appear up quickly.
> 
> Jia
> 
> > 
> > /Jarkko
> > 
> 

/Jarkko

  reply	other threads:[~2021-03-11  3:43 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-01  5:18 Tianjia Zhang
2021-03-01  9:54 ` Jarkko Sakkinen
2021-03-02  5:06   ` Tianjia Zhang
2021-03-02  5:54     ` Andy Lutomirski
2021-03-02 13:47       ` Jarkko Sakkinen
2021-03-10 12:44         ` Jia Zhang
2021-03-10 21:39           ` Jarkko Sakkinen
2021-03-11  2:47             ` Jia Zhang
2021-03-11  3:42               ` Jarkko Sakkinen [this message]
2021-03-11  4:53                 ` Tianjia Zhang
2021-03-12 16:53                   ` Jarkko Sakkinen
2021-03-11  5:55                 ` Jia Zhang
2021-03-03 12:03       ` Tianjia Zhang
2021-03-02 12:51     ` Jarkko Sakkinen
2021-03-03 12:12       ` Tianjia Zhang

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