linux-kernel - Re: [PATCH] selftests/sgx: fix EINIT failure dueto SGX_INVALID

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Date:   Fri, 12 Mar 2021 18:53:06 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Cc:     Jia Zhang <zhang.jia@...ux.alibaba.com>,
        Andy Lutomirski <luto@...capital.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Shuah Khan <shuah@...nel.org>, X86 ML <x86@...nel.org>,
        linux-sgx@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] selftests/sgx: fix EINIT failure dueto
 SGX_INVALID_SIGNATURE

On Thu, Mar 11, 2021 at 12:53:49PM +0800, Tianjia Zhang wrote:
> 
> 
> 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@...ux.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.

It does not generate keys on fly. There's a static key.

/Jarkko