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

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Date:   Mon, 26 Jun 2017 13:24:55 +0000
From:   Paul Durrant <Paul.Durrant@...rix.com>
To:     'Marek Marczykowski-Górecki' 
        <marmarek@...isiblethingslab.com>
CC:     Juergen Groß <jgross@...e.com>,
        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: 'Marek Marczykowski-Górecki'
> [mailto:marmarek@...isiblethingslab.com]
> Sent: 26 June 2017 14:22
> To: Paul Durrant <Paul.Durrant@...rix.com>
> Cc: Juergen Groß <jgross@...e.com>; 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 01:09:58PM +0000, Paul Durrant wrote:
> > > -----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.
> 
> But the issue this patch fixes applies only to hypercalls issued from HVM.

Oh, I see what you mean. Well I guess you could manually run QEMU from an HVM domain, but it would be a bit of a faff to set up.

  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?