linux-kernel - Re: Compat 32-bit syscall entry from 64-bit task!? [was: Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF]

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Date:	Wed, 18 Jan 2012 09:51:57 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Eric Paris <eparis@...hat.com>
Cc:	Indan Zupancic <indan@....nu>, Andi Kleen <andi@...stfloor.org>,
	Jamie Lokier <jamie@...reable.org>,
	Andrew Lutomirski <luto@....edu>,
	Oleg Nesterov <oleg@...hat.com>,
	Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org,
	keescook@...omium.org, john.johansen@...onical.com,
	serge.hallyn@...onical.com, coreyb@...ux.vnet.ibm.com,
	pmoore@...hat.com, djm@...drot.org, segoon@...nwall.com,
	rostedt@...dmis.org, jmorris@...ei.org, scarybeasts@...il.com,
	avi@...hat.com, penberg@...helsinki.fi, viro@...iv.linux.org.uk,
	mingo@...e.hu, akpm@...ux-foundation.org, khilman@...com,
	borislav.petkov@....com, amwang@...hat.com, ak@...ux.intel.com,
	eric.dumazet@...il.com, gregkh@...e.de, dhowells@...hat.com,
	daniel.lezcano@...e.fr, linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com,
	Roland McGrath <mcgrathr@...omium.org>
Subject: Re: Compat 32-bit syscall entry from 64-bit task!? [was: Re:
 [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF]

On Wed, Jan 18, 2012 at 7:04 AM, Eric Paris <eparis@...hat.com> wrote:
>
> 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...

That doesn't help.

Anonymous memory is the *one* kind of mapping that this cannot happen
for - because then you have the same page mapped only at one
particular virtual address (and all modern x86's are entirely coherent
in the pipeline for that case, afaik).

> 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.

So the cases that matter are file-backed and various shared memory setups.

                   Linus
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