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From:   Ricardo Ribalda <ribalda@chromium.org>
Date:   Wed, 28 Jun 2023 13:36:04 +0200
Message-ID: <CANiDSCvjCoj3Q3phbmdhdG-veHNRrfD-gBu=FuZkmrgJ2uxiJg@mail.gmail.com>
Subject: Re: [PATCH 1/1] Add a new sysctl to disable io_uring system-wide
To:     Matteo Rizzo <matteorizzo@google.com>
Cc:     Bart Van Assche <bvanassche@acm.org>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, io-uring@vger.kernel.org,
        jordyzomer@google.com, evn@google.com, poprdi@google.com,
        corbet@lwn.net, axboe@kernel.dk, asml.silence@gmail.com,
        akpm@linux-foundation.org, keescook@chromium.org,
        rostedt@goodmis.org, dave.hansen@linux.intel.com,
        chenhuacai@kernel.org, steve@sk2.org, gpiccoli@igalia.com,
        ldufour@linux.ibm.com
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Hi Matteo

On Tue, 27 Jun 2023 at 20:15, Matteo Rizzo <matteorizzo@google.com> wrote:
>
> On Tue, 27 Jun 2023 at 19:10, Bart Van Assche <bvanassche@acm.org> wrote:
> > I'm using fio + io_uring all the time on Android devices. I think we need a
> > better solution than disabling io_uring system-wide, e.g. a mechanism based
> > on SELinux that disables io_uring for apps and that keeps io_uring enabled
> > for processes started via 'adb root && adb shell ...'
>
> Android already uses seccomp to prevent untrusted applications from using
> io_uring. This patch is aimed at server/desktop environments where there is
> no easy way to set a system-wide seccomp policy and right now the only way
> to disable io_uring system-wide is to compile it out of the kernel entirely
> (not really feasible for e.g. a general-purpose distro).
>
> I thought about adding a capability check that lets privileged processes
> bypass this sysctl, but it wasn't clear to me which capability I should use.
> For userfaultfd the kernel uses CAP_SYS_PTRACE, but I wasn't sure that's
> the best choice here since io_uring has nothing to do with ptrace.
> If anyone has any suggestions please let me know. A LSM hook also sounds
> like an option but it would be more complicated to implement and use.

Have you considered that the new sysctl is "sticky like kexec_load_disabled.
When the user disables it there is no way to turn it back on until the
system is rebooted.

Best regards!

-- 
Ricardo Ribalda