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Date: Thu, 28 Feb 2013 09:31:40 +0100 (CET)
From: Jiri Kosina <>
Subject: Re: CVE request - Linux kernel: VFAT slab-based buffer

On Thu, 28 Feb 2013, Yves-Alexis Perez wrote:

> > > - not letting kernel dereference userspace pointers (and PMAP is
> > not 
> > >   available everywhere, unfortunately)
> > 
> > What do you mean by this?
> This looks like PaX KERNEXEC/UDEREF (which uses segmentation on i386 and
> code instrumentation through gcc plugins on x86_64). 

Yes, exactly. You can now apparently also add ARM to the list of 
architectures where it's been made available [1] by the grsecurity folks.


> On Ivy Bridge processors you have SMEP which will also prevent ring0 to
> execute code from unprivileged pages and on Haswell there will be SMAP
> which tries to prevent ring0 to access ring3 pages read/write when not
> needed (outside of copy_{to,from}_user for example but there are
> others).
> But, as Jiri said, this is not available everywhere so people with more
> ancient hardware can't benefit from those extensions.

Yup, sorry for my typo above, I of course meant SMAP, not PMAP.


Jiri Kosina

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