linux-kernel - Re: [PATCH v5 0/6] seccomp: add PR_SECCOMP_EXT and SECCOMP_EXT_ACT

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Date:	Mon, 2 Jun 2014 16:05:29 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Andy Lutomirski <luto@...capital.net>, linux-api@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	James Morris <james.l.morris@...cle.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Will Drewry <wad@...omium.org>, Julien Tinnes <jln@...gle.com>,
	Alexei Starovoitov <ast@...mgrid.com>
Subject: Re: [PATCH v5 0/6] seccomp: add PR_SECCOMP_EXT and SECCOMP_EXT_ACT_TSYNC

On Mon, Jun 2, 2014 at 2:17 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Mon, Jun 2, 2014 at 1:06 PM, Kees Cook <keescook@...omium.org> wrote:
>> On Mon, Jun 2, 2014 at 12:59 PM, Andy Lutomirski <luto@...capital.net> wrote:
>>> On Mon, Jun 2, 2014 at 12:47 PM, Kees Cook <keescook@...omium.org> wrote:
>>>> Hi Andrew,
>>>>
>>>> Would you be willing to carry this series? Andy Lutomirski appears
>>>> happy with it now. (Thanks again for all the feedback Andy!) If so, it
>>>> has a relatively small merge conflict with the bpf changes living in
>>>> net-next. Would you prefer I rebase against net-next, let sfr handle
>>>> it, get carried in net-next, or some other option?
>>>
>>> Well, I'm still not entirely convinced that we want to have this much
>>> multiplexing in a prctl, and I'm still a bit unconvinced that the code
>>
>> I don't want to get caught without interface argument flexibility
>> again, so that's why the prctl interface is being set up that way.
>
> I was thinking that a syscall might be a lot prettier.  It may pay to
> cc linux-api, too.
>
> I'll offer you a deal: if you try to come up with a nice, clean
> syscall, I'll try to write a fast(er) path for x86_64 to reduce
> overhead.  I bet I can save 90-100ns per syscall. :)

Now added to the Cc.

Which path do you mean to improve? Neither the prctl nor a syscall for
this would need to be fast at all.

I don't want to go in circles on this. I've been there before on my
VFS link hardening series, and my module restriction series. I would
like consensus from more than just one person. :)

I'd like to hear from other folks on this (akpm?). My instinct is to
continue using prctl since that is already where mediation for seccomp
happens. I don't see why prctl vs a new syscall makes a difference
here, frankly.

-Kees

-- 
Kees Cook
Chrome OS Security
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