Date: Mon, 22 May 2006 10:14:54 -0700
From: Andrew Morton <akpm@osdl.org>
To: Zachary Amsden <zach@vmware.com>
Cc: jakub@redhat.com, rusty@rustcorp.com.au, mingo@elte.hu,
       linux-kernel@vger.kernel.org, torvalds@osdl.org,
       virtualization@lists.osdl.org, kraxel@suse.de
Subject: Re: [PATCH] Gerd Hoffman's move-vsyscall-into-user-address-range
 patch
Message-Id: <20060522101454.52551222.akpm@osdl.org>
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Zachary Amsden <zach@vmware.com> wrote:
>
> Jakub Jelinek wrote:
> >
> > That's known bug in early glibcs short after adding vDSO support.
> > The vDSO support has been added in May 2003 to CVS glibc (i.e. post glibc
> > 2.3.2) and the problems have been fixed when they were discovered, in
> > February 2004:
> > http://sources.redhat.com/ml/libc-hacker/2004-02/msg00053.html
> > http://sources.redhat.com/ml/libc-hacker/2004-02/msg00059.html
> >
> > I strongly believe we want randomized vDSOs, people are already abusing the
> > fix mapped vDSO for attacks, and I think the unfortunate 10 months of broken
> > glibc shouldn't stop that forever.  Anyone using such glibc can still use
> > vdso=0, or do that just once and upgrade to somewhat more recent glibc.
> >   
> 
> While I'm now inclined to agree with randomization, I think the default 
> should be off.  You can quite easily "echo 1 > 
> /proc/sys/kernel/vdso_randomization" in the RC scripts, which allows you 
> to maintain compatibility for everyone and get randomization turned on 
> early enough to thwart attacks against any vulnerable daemons.
> 

It kinda sucks but yes, that's obviously least-breakage approach.  It does
mean that many people won't benefit from (and won't test!) the new feature
though.

Unless there's some sneaky way of auto-detecting a modern userspace,
perhaps (something which mounts /sys?).

All very sad.
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