linux-kernel - Re: [PATCH 3/6] seccomp: Implement constant action bitmaps

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Date:   Thu, 24 Sep 2020 01:15:24 -0700
From:   Kees Cook <keescook@...omium.org>
To:     YiFei Zhu <zhuyifei1999@...il.com>
Cc:     Jann Horn <jannh@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Will Drewry <wad@...omium.org>, bpf <bpf@...r.kernel.org>,
        YiFei Zhu <yifeifz2@...inois.edu>,
        Linux API <linux-api@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Hubertus Franke <frankeh@...ibm.com>,
        Andy Lutomirski <luto@...capital.net>,
        Valentin Rothberg <vrothber@...hat.com>,
        Dimitrios Skarlatos <dskarlat@...cmu.edu>,
        Jack Chen <jianyan2@...inois.edu>,
        Josep Torrellas <torrella@...inois.edu>,
        Tianyin Xu <tyxu@...inois.edu>,
        kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/6] seccomp: Implement constant action bitmaps

On Thu, Sep 24, 2020 at 03:07:23AM -0500, YiFei Zhu wrote:
> On Thu, Sep 24, 2020 at 2:37 AM Kees Cook <keescook@...omium.org> wrote:
> > >
> > > This belongs over into patch 1.
> >
> > Thanks! I was rushing to get this posted so YiFei Zhu wouldn't spend
> > time fighting with arch and Kconfig stuff. :) I'll clean this (and the
> > other random cruft) up.
> 
> Wait, what? I'm sorry. We have already begun fixing the mentioned
> issues (mostly the split bitmaps for different arches). Although yes
> it's nice to have another implementation to refer to so we get the
> best of both worlds (and yes I'm already copying some of the code I
> think are better here over there), don't you think it's not nice to
> say "Hey I've worked on this in June, it needed rework but I didn't
> send the newer version. Now you sent yours so I'll rush mine so your
> work is redundant."?

I was trying to be helpful: you hadn't seen the RFC, and it was missing
the emulator piece, which I wanted to be small, so I put got it out the
door today. I didn't want you to think you needed to port the larger
emulator over, for example.

> That said, I do think this should be configurable. Users would be free
> to experiment with the bitmap on or off, just like users may turn
> seccomp off entirely. A choice also allows users to select different
> implementations, a few whom I work with have ideas on how to
> accelerate / cache argument dependent syscalls, for example.

I'm open to ideas, but I want to have a non-optional performance
improvement as the first step. :) "seccomp is magically faster" was my
driving goal.

-- 
Kees Cook