linux-kernel - Re: [Xen-devel] [PATCH 2/3] xen/privcmd: Add IOCTL_PRIVCMD_DM

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Message-ID: <16ec962f-0835-1244-ddd5-e711c5d7cefd@citrix.com>
Date:   Thu, 9 Feb 2017 15:56:44 +0000
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Paul Durrant <Paul.Durrant@...rix.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: [Xen-devel] [PATCH 2/3] xen/privcmd: Add IOCTL_PRIVCMD_DM_OP

On 09/02/17 15:50, Boris Ostrovsky wrote:
>
>
> 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?

Doesn't libxc already use the hypercall buffer API for each of the buffers?

The kernel oughtn’t to need to do anything special to the user pointers
it has, other than call access_ok() on them.

~Andrew