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:	Thu, 19 Jan 2012 16:04:29 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Martin Mares <mj@....cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <ak@...ux.intel.com>, Indan Zupancic <indan@....nu>,
	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, eparis@...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,
	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]

Andi Kleen wrote:
> > Not everybody. There are programs which try hard to distinguish between
> > int80 and syscall. One such example is a sandbox for programming contests
> > I wrote several years ago. It analyses the instruction before EIP and as
> > it does not allow threads nor executing writeable memory, it should be
> > correct.
> 
> There are other ways to break it, like using the syscall itself to change
> input arguments or using ptrace from another process and other ways.
> 
> Generally there are so many races with ptrace that if you want to do
> things like that it's better to use a LSM. That's what they are for.

I could see the LSM approach working *if* there was an LSM module to
make it available to unpriviledged userspace.  I.e. a replacement for
ptrace() for this purpose.

It would be nice to be able to trace and check syscall strings properly.

-- Jamie
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