linux-kernel - Re: [PATCH 00/18] prevent bounds-check bypass via speculative execution

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Date:   Sat, 13 Jan 2018 19:33:41 +0800
From:   QingFeng Hao <haoqf@...ux.vnet.ibm.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-kernel@...r.kernel.org,
        Elena Reshetova <elena.reshetova@...el.com>
Subject: Re: [PATCH 00/18] prevent bounds-check bypass via speculative
 execution



在 2018/1/6 9:09, Dan Williams 写道:
> Quoting Mark's original RFC:
>
> "Recently, Google Project Zero discovered several classes of attack
> against speculative execution. One of these, known as variant-1, allows
> explicit bounds checks to be bypassed under speculation, providing an
> arbitrary read gadget. Further details can be found on the GPZ blog [1]
> and the Documentation patch in this series."
>
> This series incorporates Mark Rutland's latest api and adds the x86
> specific implementation of nospec_barrier. The
> nospec_{array_ptr,ptr,barrier} helpers are then combined with a kernel
> wide analysis performed by Elena Reshetova to address static analysis
> reports where speculative execution on a userspace controlled value
@Elena, can I know how did you do this analysis? I mean manually or with 
tool.
Thanks!
> could bypass a bounds check. The patches address a precondition for the
> attack discussed in the Spectre paper [2].
>
> A consideration worth noting for reviewing these patches is to weigh the
> dramatic cost of being wrong about whether a given report is exploitable
> vs the overhead nospec_{array_ptr,ptr} may introduce. In other words,
> lets make the bar for applying these patches be "can you prove that the
> bounds check bypass is *not* exploitable". Consider that the Spectre
> paper reports one example of a speculation window being ~180 cycles.
[snip]
>
>

-- 
Regards
QingFeng Hao