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Date: Thu, 28 Feb 2013 01:31:56 +0100 (CET)
From: Jiri Kosina <jikos@...os.cz>
To: oss-security@...ts.openwall.com
Subject: Re: CVE request - Linux kernel: VFAT slab-based buffer
overflow
On Wed, 27 Feb 2013, Greg KH wrote:
> > > If you know of any other ways that we can do this, please let us know.
> >
> > - W^X
>
> I thought we tried this, and had to revert it due to problems it caused
> with some dyanmic code generators. Or am I totally mistaken here?
Userspace is problematic in this respect, agreed (because of all the JIT
stuff, for example).
I am speaking more in terms of kernel now. I.e. having clear separation of
kernel RO-data and kernel code. Basically what grsecurity/PAX is doing
with their CONFIG_PAX_KERNEXEC, but with hardware support whenever
possible (i.e. minimizing runtime performance penalty).
> > - not letting kernel dereference userspace pointers (and PMAP is not
> > available everywhere, unfortunately)
>
> What do you mean by this?
If you trick kernel into derefereing pointer outside it's mapped space
(i.e. address lower than TASK_SIZE, thus fully controller by potentially
evil userspace), it'll happily do that (modulo incomplete
counter-measures, such as vm.mmap_min_addr sysctl).
Thanks,
--
Jiri Kosina
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