linux-kernel - RE: [PATCH 2/3] xen/privcmd: Add IOCTL_PRIVCMD_DM

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Message-ID: <fe50586d3cfe4eebac75bc02af9c9d58@AMSPEX02CL03.citrite.net>
Date:   Thu, 9 Feb 2017 16:45:22 +0000
From:   Paul Durrant <Paul.Durrant@...rix.com>
To:     'Boris Ostrovsky' <boris.ostrovsky@...cle.com>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Juergen Gross <jgross@...e.com>
Subject: RE: [PATCH 2/3] xen/privcmd: Add IOCTL_PRIVCMD_DM_OP

> -----Original Message-----
> From: Boris Ostrovsky [mailto:boris.ostrovsky@...cle.com]
> Sent: 09 February 2017 15:50
> To: Paul Durrant <Paul.Durrant@...rix.com>; xen-devel@...ts.xenproject.org;
> linux-kernel@...r.kernel.org
> Cc: Juergen Gross <jgross@...e.com>
> Subject: Re: [PATCH 2/3] xen/privcmd: Add IOCTL_PRIVCMD_DM_OP
> 
> 
> 
> On 02/09/2017 09:27 AM, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Paul Durrant [mailto:paul.durrant@...rix.com]
> >> Sent: 09 February 2017 14:18
> >> To: xen-devel@...ts.xenproject.org; linux-kernel@...r.kernel.org
> >> Cc: Paul Durrant <Paul.Durrant@...rix.com>; Boris Ostrovsky
> >> <boris.ostrovsky@...cle.com>; Juergen Gross <jgross@...e.com>
> >> Subject: [PATCH 2/3] xen/privcmd: Add IOCTL_PRIVCMD_DM_OP
> >>
> >> Recently a new dm_op[1] hypercall was added to Xen to provide a
> >> mechanism
> >> for restricting device emulators (such as QEMU) to a limited set of
> >> hypervisor operations, and being able to audit those operations in the
> >> kernel of the domain in which they run.
> >>
> >> This patch adds IOCTL_PRIVCMD_DM_OP as gateway for
> >> __HYPERVISOR_dm_op,
> >> bouncing the callers buffers through kernel memory to allow the address
> >> ranges to be audited (and negating the need to bounce through locked
> >> memory in user-space).
> >
> > Actually, it strikes me (now that I've posted the patch) that I should
> probably just mlock the user buffers rather than bouncing them through
> kernel... Anyway, I'd still appreciate review on other aspects of the patch.
> 
> 
> Are you suggesting that the caller (user) mlocks the buffers?

No, I meant calling get_user_pages() (which AIUI is essentially what the internals of sys_mlock does) on the buffers to make sure they don't get paged during execution of the (unlocked) ioctl.

  Paul

> 
> -boris