Subject: Re: [PATCH 00/18] prevent bounds-check bypass via speculative
 execution
To: Dan Williams <dan.j.williams@intel.com>,
        linux-kernel@vger.kernel.org
Cc: Mark Rutland <mark.rutland@arm.com>, peterz@infradead.org,
        Alan Cox <alan.cox@intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Will Deacon <will.deacon@arm.com>,
        Solomon Peachy <pizza@shaftnet.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Christian Lamparter <chunkeey@googlemail.com>,
        Elena Reshetova <elena.reshetova@intel.com>,
        linux-arch@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
        "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>,
        linux-scsi@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
        x86@kernel.org, Ingo Molnar <mingo@redhat.com>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Zhang Rui <rui.zhang@intel.com>, linux-media@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>, Jan Kara <jack@suse.com>,
        Eduardo Valentin <edubezval@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>, qla2xxx-upstream@qlogic.com,
        tglx@linutronix.de, Mauro Carvalho Chehab <mchehab@kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Kalle Valo <kvalo@codeaurora.org>, alan@linux.intel.com,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        gregkh@linuxfoundation.org, linux-wireless@vger.kernel.org,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        netdev@vger.kernel.org, torvalds@linux-foundation.org,
        "David S. Miller" <davem@davemloft.net>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        dan.carpenter@oracle.com
References: <151520099201.32271.4677179499894422956.stgit@dwillia2-desk3.amr.corp.intel.com>
From: Florian Fainelli <f.fainelli@gmail.com>
Message-ID: <ca6f24c0-d6cf-e309-aa68-92f1378ee75a@gmail.com>
Date: Sat, 6 Jan 2018 10:56:25 -0800
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Le 01/05/18 à 17:09, Dan Williams a écrit :
> 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
> 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.
> 
> Note that there is also a proposal from Linus, array_access [3], that
> attempts to quash speculative execution past a bounds check without
> introducing an lfence instruction. That may be a future optimization
> possibility that is compatible with this api, but it would appear to
> need guarantees from the compiler that it is not clear the kernel can
> rely on at this point. It is also not clear that it would be a
> significant performance win vs lfence.
> 
> These patches also will also be available via the 'nospec' git branch
> here:
> 
>     git://git.kernel.org/pub/scm/linux/kernel/git/djbw/linux nospec

Although I suppose -stable and distribution maintainers will keep a
close eye on these patches, is there a particular reason why they don't
include the relevant CVE number in their commit messages?

It sounds like Coverity was used to produce these patches? If so, is
there a plan to have smatch (hey Dan) or other open source static
analysis tool be possibly enhanced to do a similar type of work?

Thanks!
-- 
Florian