linux-kernel - RE: [Xen-devel] [PATCH] x86/xen: allow userspace access during hypercalls

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Date:   Mon, 26 Jun 2017 13:09:58 +0000
From:   Paul Durrant <Paul.Durrant@...rix.com>
To:     'Marek Marczykowski-Górecki' 
        <marmarek@...isiblethingslab.com>,
        Juergen Groß <jgross@...e.com>
CC:     Andrew Cooper <Andrew.Cooper3@...rix.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: RE: [Xen-devel] [PATCH] x86/xen: allow userspace access during
        hypercalls

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@...ts.xen.org] On Behalf Of
> Marek Marczykowski-Górecki
> Sent: 26 June 2017 13:45
> To: Juergen Groß <jgross@...e.com>
> Cc: Andrew Cooper <Andrew.Cooper3@...rix.com>; x86@...nel.org; linux-
> kernel@...r.kernel.org; stable@...r.kernel.org; xen-
> devel@...ts.xenproject.org; Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Subject: Re: [Xen-devel] [PATCH] x86/xen: allow userspace access during
> hypercalls
> 
> On Mon, Jun 26, 2017 at 02:05:48PM +0200, Juergen Groß wrote:
> > On 06/23/2017 02:47 PM, Marek Marczykowski-Górecki wrote:
> > > Userspace application can do a hypercall through /dev/xen/privcmd, and
> > > some for some hypercalls argument is a pointers to user-provided
> > > structure. When SMAP is supported and enabled, hypervisor can't access.
> > > So, lets allow it.
> >
> > What about HYPERVISOR_dm_op?
> 
> Indeed, arguments copied to kernel space there are only addresses of
> buffers. Will send v2 in a moment.
> But I can't test it right now, as for my understanding this require
> HVM/PVHv2 dom0 or stubdomain...
> 

No, you don't need anything particularly special to use dm_op. Just up-to-date xen, privcmd, and QEMU. QEMU should end up using dm_op by default if all three are in place.

  Paul

> --
> Best Regards,
> Marek Marczykowski-Górecki
> Invisible Things Lab
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?