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From: Eric Paris <eparis@redhat.com>
Subject: Re: Compat 32-bit syscall entry from 64-bit task!? [was: Re:
 [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF]
Date: Wed, 18 Jan 2012 10:04:43 -0500
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Cc: Indan Zupancic <indan@nul.nu>, Andi Kleen <andi@firstfloor.org>,
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To: Linus Torvalds <torvalds@linux-foundation.org>
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On Tue, 2012-01-17 at 22:25 -0800, Linus Torvalds wrote:

> Of course, limiting things so that you cannot map the same page
> executably *and* writably is one solution - and a good idea regardless
> - so secure environments can still exist. But even then you could have
> races in a multi-threaded environment (they'd just be *much* harder to
> trigger for an attacker).

Gratuitous SELinux for the win e-mail!  (Feel free to delete now)  We
typically, for all confined domains, do not allow mapping anonymous
memory both W and X.  Actually you can't even map it W and then map it
X...

Now if there is file which you have both W and X SELinux permissions
(which is rare, but not impossible) you could map it in two places.  So
we can (and do) build SELinux sandboxes which address this.