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From:   Jann Horn <jannh@google.com>
Date:   Mon, 12 Oct 2020 08:49:56 +0200
Message-ID: <CAG48ez2rutKsgpvYeN+TqmhkJe4U7Sxr0oqyrjhUQaePGZg4uA@mail.gmail.com>
Subject: Re: [PATCH v5 seccomp 5/5] seccomp/cache: Report cache data through /proc/pid/seccomp_cache
To:     YiFei Zhu <zhuyifei1999@gmail.com>
Cc:     Linux Containers <containers@lists.linux-foundation.org>,
        YiFei Zhu <yifeifz2@illinois.edu>, bpf <bpf@vger.kernel.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Aleksa Sarai <cyphar@cyphar.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andy Lutomirski <luto@amacapital.net>,
        David Laight <David.Laight@aculab.com>,
        Dimitrios Skarlatos <dskarlat@cs.cmu.edu>,
        Giuseppe Scrivano <gscrivan@redhat.com>,
        Hubertus Franke <frankeh@us.ibm.com>,
        Jack Chen <jianyan2@illinois.edu>,
        Josep Torrellas <torrella@illinois.edu>,
        Kees Cook <keescook@chromium.org>,
        Tianyin Xu <tyxu@illinois.edu>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
        Tycho Andersen <tycho@tycho.pizza>,
        Valentin Rothberg <vrothber@redhat.com>,
        Will Drewry <wad@chromium.org>
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On Sun, Oct 11, 2020 at 5:48 PM YiFei Zhu <zhuyifei1999@gmail.com> wrote:
> Currently the kernel does not provide an infrastructure to translate
> architecture numbers to a human-readable name. Translating syscall
> numbers to syscall names is possible through FTRACE_SYSCALL
> infrastructure but it does not provide support for compat syscalls.
>
> This will create a file for each PID as /proc/pid/seccomp_cache.
> The file will be empty when no seccomp filters are loaded, or be
> in the format of:
> <arch name> <decimal syscall number> <ALLOW | FILTER>
> where ALLOW means the cache is guaranteed to allow the syscall,
> and filter means the cache will pass the syscall to the BPF filter.
>
> For the docker default profile on x86_64 it looks like:
> x86_64 0 ALLOW
> x86_64 1 ALLOW
> x86_64 2 ALLOW
> x86_64 3 ALLOW
> [...]
> x86_64 132 ALLOW
> x86_64 133 ALLOW
> x86_64 134 FILTER
> x86_64 135 FILTER
> x86_64 136 FILTER
> x86_64 137 ALLOW
> x86_64 138 ALLOW
> x86_64 139 FILTER
> x86_64 140 ALLOW
> x86_64 141 ALLOW
> [...]
>
> This file is guarded by CONFIG_SECCOMP_CACHE_DEBUG with a default
> of N because I think certain users of seccomp might not want the
> application to know which syscalls are definitely usable. For
> the same reason, it is also guarded by CAP_SYS_ADMIN.
>
> Suggested-by: Jann Horn <jannh@google.com>
> Link: https://lore.kernel.org/lkml/CAG48ez3Ofqp4crXGksLmZY6=fGrF_tWyUCg7PBkAetvbbOPeOA@mail.gmail.com/
> Signed-off-by: YiFei Zhu <yifeifz2@illinois.edu>

Reviewed-by: Jann Horn <jannh@google.com>