linux-kernel - Re: [PATCH 2/4] selftests/sgx: Fix Q1 and Q2 calculation in sigstruct.c

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Date:   Wed, 7 Jul 2021 02:52:17 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
        linux-sgx@...r.kernel.org,
        Reinette Chatre <reinette.chatre@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jethro Beekman <jethro@...tanix.com>,
        Borislav Petkov <bp@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] selftests/sgx: Fix Q1 and Q2 calculation in
 sigstruct.c

On Tue, Jul 06, 2021 at 01:53:20PM -0700, Dave Hansen wrote:
> On 7/5/21 7:36 AM, Jarkko Sakkinen wrote:
> > From: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
> > 
> > Q1 and Q2 are numbers with *maximum* length of 384 bytes. If the calculated
> > length of Q1 and Q2 is less than 384 bytes, things will go wrong.
> > 
> > E.g. if Q2 is 383 bytes, then
> > 
> > 1. The bytes of q2 are copied to sigstruct->q2 in calc_q1q2().
> > 2. The entire sigstruct->q2 is reversed, which results it being
> >    256 * Q2, given that the last byte of sigstruct->q2 is added
> >    to before the bytes given by calc_q1q2().
> > 
> > Either change in key or measurement can trigger the bug. E.g. an unmeasured
> > heap could cause a devastating change in Q1 or Q2.
> > 
> > Reverse exactly the bytes of Q1 and Q2 in calc_q1q2() before returning to
> > the caller.
> > 
> > Fixes: 2adcba79e69d ("selftests/x86: Add a selftest for SGX")
> > Link: https://lore.kernel.org/linux-sgx/20210301051836.30738-1-tianjia.zhang@linux.alibaba.com/
> > Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
> > Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
> 
> This looks fine, but can I suggest a Subject: tweak?
> 
> 	selftests/sgx: Fix calculations for sub-maximum field sizes

WFM

> 
> In any case:
> 
> Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>

Thank you.

/Jarkko