linux-kernel - Re: [PULL] vhost: cleanups and fixes

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Message-ID: <CAHk-=wibzqo7C+mS+BgZxRbgdWe2w5F39EhuFUhZUxvotoGLuA@mail.gmail.com>
Date:   Fri, 2 Nov 2018 10:10:45 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     mst@...hat.com
Cc:     mark.rutland@....com, Kees Cook <keescook@...omium.org>,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        bijan.mottahedeh@...cle.com, gedwards@....com, joe@...ches.com,
        lenaic@...ard.fr, liang.z.li@...el.com, mhocko@...nel.org,
        mhocko@...e.com, stefanha@...hat.com, wei.w.wang@...el.com,
        jasowang@...hat.com
Subject: Re: [PULL] vhost: cleanups and fixes

On Fri, Nov 2, 2018 at 9:59 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> Just for completeness I'd like to point out for vhost the copies are
> done from the kernel thread.  So yes we can switch to copy_to/from_user
> but for e.g. 32-bit userspace running on top of a 64 bit kernel it is
> IIUC not sufficient - we must *also* do access_ok checks on control path
> when addresses are passed to the kernel and when current points to the
> correct task struct.

Don't you take over the VM with "use_mm()" when you do the copies? So
yes, it's a kernel thread, but it has a user VM, and though that
should have the user limits.

No?

          Linus