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

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Message-ID: <CABqSeAS=b6NQ=mqrD=hV60md3isYSDyAnE9QE_AT4=oYYFkAfQ@mail.gmail.com>
Date:   Wed, 23 Sep 2020 19:36:47 -0500
From:   YiFei Zhu <zhuyifei1999@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Jann Horn <jannh@...gle.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Tycho Andersen <tycho@...ho.pizza>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Dimitrios Skarlatos <dskarlat@...cmu.edu>,
        Valentin Rothberg <vrothber@...hat.com>,
        Hubertus Franke <frankeh@...ibm.com>,
        bpf <bpf@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        linux-api@...r.kernel.org,
        kernel list <linux-kernel@...r.kernel.org>,
        Jack Chen <jianyan2@...inois.edu>,
        Josep Torrellas <torrella@...inois.edu>,
        Tianyin Xu <tyxu@...inois.edu>,
        YiFei Zhu <yifeifz2@...inois.edu>
Subject: Re: [PATCH 3/6] seccomp: Implement constant action bitmaps

On Wed, Sep 23, 2020 at 6:29 PM Kees Cook <keescook@...omium.org> wrote:
> In order to optimize these cases from O(n) to O(1), seccomp can
> use bitmaps to immediately determine the desired action. A critical
> observation in the prior paragraph bears repeating: the common case for
> syscall tests do not check arguments. For any given filter, there is a
> constant mapping from the combination of architecture and syscall to the
> seccomp action result. (For kernels/architectures without CONFIG_COMPAT,
> there is a single architecture.). As such, it is possible to construct
> a mapping of arch/syscall to action, which can be updated as new filters
> are attached to a process.

Would you mind educating me how this patch plan one handling MIPS? For
one kernel they seem to have up to three arch numbers per build,
AUDIT_ARCH_MIPS{,64,64N32}. Though ARCH_TRACE_IGNORE_COMPAT_SYSCALLS
does not seem to be defined for MIPS so I'm assuming the syscall
numbers are the same, but I think it is possible some client uses that
arch number to pose different constraints for different processes, so
it would better not accelerate them rather than break them.


YiFei Zhu