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

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Date:	Thu, 09 Feb 2012 06:47:54 -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, 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>,
	"H.J. Lu" <hjl.tools@...il.com>
Subject: Re: Compat 32-bit syscall entry from 64-bit task!?

On 02/08/2012 10:03 PM, Indan Zupancic wrote:
>
> You can check the syscall instruction itself, either before it's executed
> or afterwards by checking the IP. Though that's trickier, because the
> kernel points the IP to just after int80 for a sysenter call, so you have
> to check if there's a sysenter nearby too.
>

No, that's a total nightmare.  FAIL.

> But the kernel is actually changing the registers, so why hide that?
>
> I mean, once user space is aware that the kernel may do swizzling, is there
> any actual problem left? Because this sounds like user space was trying to
> be clever, but got it wrong. E.g. it knew the kernel was entered not via
> int80, but then got confused because of the swizzling.

I would be great if we didn't have an existing compatibility problem. 
As it is we can't get rid of it easily.

	-hpa

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