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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Message-ID: <20120118015013.GR11715@one.firstfloor.org>
Date:	Wed, 18 Jan 2012 02:50:13 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Indan Zupancic <indan@....nu>
Cc:	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,
	torvalds@...ux-foundation.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>,
	Andi Kleen <andi@...stfloor.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]

> Our ptrace jailer is checking cs to figure out if a task is a compat task
> or not, if the kernel can change that behind our back it means our jailer

Every user program change it behind your back.

Your ptrace jailer isn't.

> I think this behaviour is so unexpected that it can only cause security
> problems in the long run. Is anyone counting on this? Where is this
> behaviour documented?

Look up far jumps in any x86 manual.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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