From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: Bisected Xen-unstable: "Segment register inaccessible for d1v0" when starting HVM guest on intel Date: Wed, 2 Jul 2014 11:37:04 +0100 Message-ID: <53B3E0D0.4040503@citrix.com> References: <1057886355.20140628222158@eikelenboom.it> <53B1A244020000780001EA4D@mail.emea.novell.com> <1081819750.20140630183750@eikelenboom.it> <53B19EEB.4060603@citrix.com> <53B27902020000780001ED8B@mail.emea.novell.com> <53B29E03020000780001EF03@mail.emea.novell.com> <53B3CA8A020000780001F4B4@mail.emea.novell.com> <53B3D5D2020000780001F4F8@mail.emea.novell.com> <53B3ECEE020000780001F61F@mail.emea.novell.com> <53B3D491.1080907@citrix.com> <53B3F324020000780001F66B@mail.emea.novell.com> <53B3D8CD.1050506@citrix.com> <53B3F603020000780001F687@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1X2HuY-0006gI-Sh for xen-devel@lists.xenproject.org; Wed, 02 Jul 2014 10:37:10 +0000 In-Reply-To: <53B3F603020000780001F687@mail.emea.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: Sander Eikelenboom , Feng Wu , "xen-devel@lists.xenproject.org" List-Id: xen-devel@lists.xenproject.org On 02/07/14 11:07, Jan Beulich wrote: >>>> On 02.07.14 at 12:02, wrote: >>> Just like copy_to_user() would produce -EFAULT for a hypercall >>> when used on a non-present page or a non-canonical address, it >>> should (and afaict will with how things are right now) similarly >>> produce -EFAULT for an attempted access to a guest-accessible >>> page when the current mode of the guest is supervisor. >>> >>> To me it is a logical extension to also fail accesses outside of >>> hypercalls or emulation. >> Consider an HVM guest with SMAP in effect, making a hypercall. If a >> guest handle points to guest userspace, Xen would be unable to ever >> complete the hypercall without an -EFAULT. >> >> I don't think this is reasonable to fail. > This is very reasonable to fail: Such an operation violates the SMAP > guarantees. If the kernel wants to permit this, it needs to CLAC/STAC > around the hypercall in its privcmd (or alike) driver. > > Jan > Hmm - I suppose. At least this gives the guest operating system a choice. ~Andrew