linux-kernel - Re: [PATCH v2 seccomp 2/6] asm/syscall.h: Add syscall

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Message-ID: <CAG48ez2R1fF2kAUc7vOOFgaE482jA94Lx+0oWiy6M5JeM2HtvA@mail.gmail.com>
Date:   Fri, 25 Sep 2020 02:15:50 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     YiFei Zhu <yifeifz2@...inois.edu>,
        YiFei Zhu <zhuyifei1999@...il.com>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        bpf <bpf@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dimitrios Skarlatos <dskarlat@...cmu.edu>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Hubertus Franke <frankeh@...ibm.com>,
        Jack Chen <jianyan2@...inois.edu>,
        Josep Torrellas <torrella@...inois.edu>,
        Tianyin Xu <tyxu@...inois.edu>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Tycho Andersen <tycho@...ho.pizza>,
        Valentin Rothberg <vrothber@...hat.com>,
        Will Drewry <wad@...omium.org>
Subject: Re: [PATCH v2 seccomp 2/6] asm/syscall.h: Add syscall_arches[] array

On Fri, Sep 25, 2020 at 2:01 AM Kees Cook <keescook@...omium.org> wrote:
> 2) seccomp needs to handle "multiplexed" tables like x86_x32 (distros
>    haven't removed CONFIG_X86_X32 widely yet, so it is a reality that
>    it must be dealt with), which means seccomp's idea of the arch
>    "number" can't be the same as the AUDIT_ARCH.

Sure, distros ship it; but basically nobody uses it, it doesn't have
to be fast. As long as we don't *break* it, everything's fine. And if
we ignore the existence of X32 in the fastpath, that'll just mean that
syscalls with the X32 marker bit always hit the seccomp slowpath
(because it'll look like the syscall number is out-of-bounds ) - no
problem.