linux-kernel - Re: [PATCH] Protection for exploiting null dereference using mmap

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Message-ID: <20070607142802.GB9094@ucw.cz>
Date:	Thu, 7 Jun 2007 14:28:02 +0000
From:	Pavel Machek <pavel@....cz>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Eric Paris <eparis@...hat.com>, Alan Cox <alan@...hat.com>,
	James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
	selinux@...ho.nsa.gov, drepper@...hat.com, roland@...hat.com,
	arjan@...radead.org, mingo@...e.hu, viro@...iv.linux.org.uk,
	chrisw@...hat.com, sds@...ho.nsa.gov, sgrubb@...hat.com
Subject: Re: [PATCH] Protection for exploiting null dereference using mmap

Hi!

> > While I understand, there are a few users who will have problems with
> > this default are we really better to not provide this defense in depth
> > for the majority of users and let those with problems turn it off rather
> > than provide no defense by default?  I could even provide a different
> > default for SELinux and non-SELinux if anyone saw value in that?  But if
> > others think that off default is  best I'll send another patch shortly
> > with the unsigned long fix and the default set to 0.  My hope is then
> > that distros will figure out to turn this on.
> > 
> 
> I hope not.  This breaks any hardware virtualizer.
> 
> So yes, we're better off not having this on, and require it to be
> explicitly enabled by the end user.

You could do something like 4G+4G patches.... but performance penalty
would be ugly.

But no, we cant break userspace 'by default'.
							Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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