Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 24 Sep 2020 00:12:19 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Jann Horn <jannh@google.com>
Cc:     YiFei Zhu <yifeifz2@illinois.edu>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Tycho Andersen <tycho@tycho.pizza>,
        Andy Lutomirski <luto@amacapital.net>,
        Will Drewry <wad@chromium.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Giuseppe Scrivano <gscrivan@redhat.com>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
        Dimitrios Skarlatos <dskarlat@cs.cmu.edu>,
        Valentin Rothberg <vrothber@redhat.com>,
        Hubertus Franke <frankeh@us.ibm.com>,
        Jack Chen <jianyan2@illinois.edu>,
        Josep Torrellas <torrella@illinois.edu>,
        Tianyin Xu <tyxu@illinois.edu>, bpf <bpf@vger.kernel.org>,
        Linux Containers <containers@lists.linux-foundation.org>,
        Linux API <linux-api@vger.kernel.org>,
        kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/6] x86: Enable seccomp architecture tracking
Message-ID: <202009240011.A56710DC@keescook>
References: <20200923232923.3142503-1-keescook@chromium.org>
 <20200923232923.3142503-3-keescook@chromium.org>
 <CAG48ez1BXWdWA5zPzOD21bQ4RsHQ6bSDWR8soTkkNphJ=zdHWw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAG48ez1BXWdWA5zPzOD21bQ4RsHQ6bSDWR8soTkkNphJ=zdHWw@mail.gmail.com>
Precedence: bulk

On Thu, Sep 24, 2020 at 02:45:45AM +0200, Jann Horn wrote:
> On Thu, Sep 24, 2020 at 1:29 AM Kees Cook <keescook@chromium.org> wrote:
> > Provide seccomp internals with the details to calculate which syscall
> > table the running kernel is expecting to deal with. This allows for
> > efficient architecture pinning and paves the way for constant-action
> > bitmaps.
> [...]
> > diff --git a/arch/x86/include/asm/seccomp.h b/arch/x86/include/asm/seccomp.h
> [...]
> > +#ifdef CONFIG_X86_64
> [...]
> > +#else /* !CONFIG_X86_64 */
> > +# define SECCOMP_ARCH                                  AUDIT_ARCH_I386
> > +#endif
> 
> If we are on a 32-bit kernel, performing architecture number checks in
> the kernel is completely pointless, because we know that there is only
> a single architecture identifier under which syscalls can happen.
> 
> While this patch is useful for enabling the bitmap logic in the
> following patches, I think it adds unnecessary overhead in the context
> of the previous patch.

That's what the RFC was trying to do (avoid the logic if there is only a
single arch known to the kernel). I will rework this a bit harder. :)

-- 
Kees Cook