Re: [PATCH] Gerd Hoffman's move-vsyscall-into-user-address-range patch

Andrew Morton
2006-05-22T17:16:07Z

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.