Re: [PATCH 1/1] Add a new sysctl to disable io_uring system-wide

[Ricardo Ribalda <ribalda@chromium.org>]

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