svn commit: r275742 - in stable: 10/contrib/llvm/lib/Transforms/Vectorize 10/sys/sys 9/contrib/llvm/lib/Transforms/Vectorize 9/sys/sys

[Dimitry Andric]

On 14 Dec 2014, at 15:54, Steven Hartland <steven at multiplay.co.uk> wrote:
> 
> 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
>> 
>> 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.html
>>   https://lists.freebsd.org/pipermail/freebsd-toolchain/2014-September/001211.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
> 
> 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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