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

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Message-ID: <CALCETrXB0zp8gwpWuxXs0bgB8sQhe6JLE46BOYw3OrBx7hQYVw@mail.gmail.com>
Date:	Mon, 2 Jun 2014 14:17:49 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Kees Cook <keescook@...omium.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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 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. :)

>
>> wouldn't be better off it it were completely atomic in the sense that
>> it would either work or fail without doing anything.
>
> Getting perfect atomic operation looks extremely hard given task
> locking. If this could get fixed in the future, it would have no
> impact on the interface. At present, the corner case of the racing
> thread is small enough that just catching the race failure is
> sufficient. If task locking is improved in the future, it could just
> simply never lose a race. Userspace still needs to handle errors no
> matter what is the non-race failure condition (mode 1 or forked
> filter) still exists.
>

I think it's doable -- I just replied to the other thread.

> -Kees
>
> --
> Kees Cook
> Chrome OS Security



-- 
Andy Lutomirski
AMA Capital Management, LLC
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