Re: [GIT PULL] x86/kaslr for v3.14

From: Ingo Molnar
Date: Tue Jan 21 2014 - 09:39:50 EST

* H. Peter Anvin <hpa@xxxxxxxxx> wrote:

> On 01/21/2014 01:00 AM, Peter Zijlstra wrote:
> >>
> >> So this is presumably something that needs to be fixed in perf?
> >
> > Where do we learn about the offset from userspace?
> >
> Now this is tricky... if this offset is too easy to get it
> completely defeats kASLR. On the other hand, I presume that if we
> are exporting /proc/kcore we're not secure anyway. Kees, I assume
> that in "secure" mode perf annotations simply wouldn't work anyway?

So /proc/kcore is:

aldebaran:~> ls -l /proc/kcore
-r-------- 1 root root 140737486266368 Jan 21 15:35 /proc/kcore

i.e. root only.

The thing is, one of my first remarks on this whole KASLR series was
that tooling needs to work. I suggested that the kernel should only
expose non-randomized addresses and that all facilities need to
continue to 'just work' with those. That argument was ignored AFAICS
and the problem still isn't solved.

I'd argue that solving it in the kernel instead of making all tooling
variants aware of KASLR one by one is a far more intelligent and
efficient solution ...


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