linux-kernel - Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF

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Date:	Tue, 17 Jan 2012 13:35:59 -0600
From:	Will Drewry <wad@...omium.org>
To:	Oleg Nesterov <oleg@...hat.com>, Indan Zupancic <indan@....nu>
Cc:	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, luto@....edu, 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: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF

On Tue, Jan 17, 2012 at 10:56 AM, Will Drewry <wad@...omium.org> wrote:
> On Tue, Jan 17, 2012 at 10:45 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>> On 01/16, Will Drewry wrote:
>>>
>>> On Mon, Jan 16, 2012 at 12:37 PM, Oleg Nesterov <oleg@...hat.com> wrote:
>>> >
>>> > Yes, thanks, I forgot about compat tasks again. But this is easy, just
>>> > we need regs_64_to_32().
>>>
>>> Yup - we could make the assumption that is_compat_task is always
>>> 32-bit and the pt_regs is always 64-bit, then copy_and_truncate with
>>> regs_64_to_32.  Seems kinda wonky though :/
>>
>> much simpler/faster than what regset does to create the artificial
>> user_regs_struct32.
>
> True, I could collapse pt_regs to looks like the exported ABI pt_regs.
>  Then only compat processes would get the copy overhead.  That could
> be tidy and not break ABI.  It would mean that I have to assume that
> if unsigned long == 64-bit and is_compat_task(), then the task is
> 32-bit.  Do you think if we ever add a crazy 128-bit "supercomputer"
> arch that we will add a is_compat64_task() so that I could properly
> collapse? :)
>
> I like this idea!

Ouch, so a few issues:
- pt_regs isn't exported for most arches
- is_compat_task arches would need custom fixups

I think Indan takes this round :) I'll being integrating a
syscall_get_arguments approach.  Hopefully it can be quite efficient.

cheers!
will
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