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

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Message-ID: <CABqD9hZg4sKiVMS-g5ed7-HKOaiUb06y05TL=QkfBkm9kVmquA@mail.gmail.com>
Date:	Thu, 12 Jan 2012 11:51:54 -0600
From:	Will Drewry <wad@...omium.org>
To:	Oleg Nesterov <oleg@...hat.com>
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,
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	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 Thu, Jan 12, 2012 at 11:23 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> 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.

I don't either :/  My original idea was to operate on task_pt_regs(current),
but I noticed that PTRACE_GETREGS/SETREGS only uses the
user_regs_struct. So I went that route.

I'd love for pt_regs to be fair game to cut down on the copying!
will
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