linux-kernel - Re: Compat 32-bit syscall entry from 64-bit task!?

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Date:	Wed, 18 Jan 2012 18:16:23 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Indan Zupancic <indan@....nu>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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, 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,
	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!?

On 01/18/2012 05:45 PM, Indan Zupancic wrote:
> 
> For security reasons it should be impossible for userspace to set those bits
> themselves, otherwise the tracer can be easily fooled on an old kernel. That
> seems to be the case for the higher bits of eflags, so eflags would work. And
> the current code checks cs, also checking eflags would be very easy to add.
> 

I think this goes without saying, and isn't an issue for the options
currently on the table (including regset).

	-phpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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