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:	Tue, 17 Jan 2012 18:46:11 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	Jamie Lokier <jamie@...reable.org>,
	Andi Kleen <andi@...stfloor.org>,
	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]

On Tue, Jan 17, 2012 at 6:31 PM, Andi Kleen <ak@...ux.intel.com> wrote:
>
> That would be incompatible.

No it wouldn't.

We'd only do it for the case that everybody gets wrong: int80 from a
64-bit context.

All the other cases are trivial to see (look at CS to determine 32-bit
vs 64-bit system call) and are the common case.

So the one new "incompatible" bit case would be the case that existing
users would inevitably get wrong, so it can hardly be "incompatible".

                  Linus
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