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

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Message-ID: <20120112172315.GA26295@redhat.com>
Date:	Thu, 12 Jan 2012 18:23:15 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Will Drewry <wad@...omium.org>
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
Subject: Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using
	BPF

On 01/12, Will Drewry wrote:
>
> On Thu, Jan 12, 2012 at 10:22 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> >> +      */
> >> +     regs = seccomp_get_regs(regs_tmp, &regs_size);
> >
> > Stupid question. I am sure you know what are you doing ;) and I know
> > nothing about !x86 arches.
> >
> > But could you explain why it is designed to use user_regs_struct ?
> > Why we can't simply use task_pt_regs() and avoid the (costly) regsets?
>
> So on x86 32, it would work since user_regs_struct == task_pt_regs
> (iirc), but on x86-64
> and others, that's not true.

Yes sure, I meant that userpace should use pt_regs too.

> If it would be appropriate to expose pt_regs to userspace, then I'd
> happily do so :)

Ah, so that was the reason. But it is already exported? At least I see
the "#ifndef __KERNEL__" definition in arch/x86/include/asm/ptrace.h.

Once again, I am not arguing, just trying to understand. And I do not
know if this definition is part of abi.

Oleg.

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