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Date:      Sun, 14 Dec 2014 16:11:09 +0100
From:      Dimitry Andric <dim@FreeBSD.org>
To:        Steven Hartland <steven@multiplay.co.uk>
Cc:        svn-src-stable@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, svn-src-stable-10@freebsd.org
Subject:   Re: svn commit: r275742 - in stable: 10/contrib/llvm/lib/Transforms/Vectorize 10/sys/sys 9/contrib/llvm/lib/Transforms/Vectorize 9/sys/sys
Message-ID:  <43A88D44-A799-46AB-8853-560407BABC84@FreeBSD.org>
In-Reply-To: <548DA4A3.8020000@freebsd.org>
References:  <201412131214.sBDCESwJ033037@svn.freebsd.org> <548DA4A3.8020000@freebsd.org>

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On 14 Dec 2014, at 15:54, Steven Hartland <steven@multiplay.co.uk> =
wrote:
>=20
> On 13/12/2014 12:14, Dimitry Andric wrote:
>> Author: dim
>> Date: Sat Dec 13 12:14:26 2014
>> New Revision: 275742
>> URL: https://svnweb.freebsd.org/changeset/base/275742
>>=20
>> Log:
>>   MFC r275633:
>>      Pull in r223171 from upstream llvm trunk (by Michael =
Zolotukhin):
>>        PR21302. Vectorize only bottom-tested loops.
>>        rdar://problem/18886083
>>      This fixes a bug in the llvm vectorizer, which could sometimes =
cause
>>   vectorized loops to perform an additional iteration, leading to =
possible
>>   buffer overruns.  Symptoms of this, which are usually segfaults, =
were
>>   first noticed when building gcc ports, here:
>>      =
https://lists.freebsd.org/pipermail/freebsd-ports/2014-September/095466.ht=
ml
>>   =
https://lists.freebsd.org/pipermail/freebsd-toolchain/2014-September/00121=
1.html
>>      Since this fix is very important for ports, bump =
__FreeBSD_version to
>>   make it easier for port maintainers to test whether the fix has =
been
>>   applied.
>>      Upstream PR:	http://llvm.org/PR21302
>=20
> Sounds nasty, is this something that only effects stable/10 or does it =
also effects 10.1-RELEASE?

Yes, this is quite nasty, and it does affect 10.1-RELEASE, 9.3-RELEASE,
and any other release with clang 3.4.x, which turned on the vectorizer
by default.

Although it is in fact rather hard to create the situation where it can
possibly do an off-by-one, I would really advise to apply this diff to
release systems as well.

I also contacted secteam@ about it, but apparently they have not yet
decided whether to do a security advisory for this bug.

-Dimitry


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