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

Jarkko Sakkinen
2021-07-06T23:52:23Z

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@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

WFM

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

Thank you.

/Jarkko