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Subject: Re: [PATCH 2/4] selftests/sgx: Fix Q1 and Q2 calculation in
 sigstruct.c
To:     Jarkko Sakkinen <jarkko@kernel.org>, Shuah Khan <shuah@kernel.org>
Cc:     linux-kselftest@vger.kernel.org, linux-sgx@vger.kernel.org,
        Reinette Chatre <reinette.chatre@intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Tianjia Zhang <tianjia.zhang@linux.alibaba.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Jethro Beekman <jethro@fortanix.com>,
        Borislav Petkov <bp@suse.de>, linux-kernel@vger.kernel.org
References: <20210705143652.116125-1-jarkko@kernel.org>
 <20210705143652.116125-3-jarkko@kernel.org>
From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <4303b822-5861-ba2c-f620-0e752e499329@intel.com>
Date:   Tue, 6 Jul 2021 13:53:20 -0700
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On 7/5/21 7:36 AM, Jarkko Sakkinen wrote:
> From: Tianjia Zhang <tianjia.zhang@linux.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@linux.alibaba.com>
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

This looks fine, but can I suggest a Subject: tweak?

	selftests/sgx: Fix calculations for sub-maximum field sizes

In any case:

Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>