From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH 4/4] xen/public: arm: rework the macro set_xen_guest_handle_raw Date: Wed, 4 Nov 2015 14:42:24 +0000 Message-ID: <563A1950.8050308@citrix.com> References: <1446228813-2593-1-git-send-email-julien.grall@citrix.com> <1446228813-2593-5-git-send-email-julien.grall@citrix.com> <1446554124.10390.19.camel@citrix.com> <5638BE43.4080607@citrix.com> <1446561267.10390.48.camel@citrix.com> <5639E949.6020800@citrix.com> <1446636465.6461.70.camel@citrix.com> <5639EEB6.6040908@citrix.com> <1446647350.6461.89.camel@citrix.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 1ZtzI3-0002M7-PZ for xen-devel@lists.xenproject.org; Wed, 04 Nov 2015 14:43:55 +0000 In-Reply-To: <1446647350.6461.89.camel@citrix.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: Ian Campbell , Stefano Stabellini Cc: xen-devel@lists.xenproject.org, Keir Fraser , Ian Jackson , Jan Beulich , Tim Deegan List-Id: xen-devel@lists.xenproject.org On 04/11/15 14:29, Ian Campbell wrote: >>>>> This looses out on the arm32 hypervisor sanity checking that the >>>>> padding >>>>> bytes are 0 (as required by the ABI) but TBH I haven't checked that >>>>> the >>>>> current version has that property either. >>>> >>>> It's done during the assignation by the compiler: >>>> >>>> (hnd).q = (uint64_t)(uintptr_t)(val); >>> >>> I meant on the reading side. >> >> It's the responsibility of the caller to zero the padding. There is >> nothing to do on the reading side, the hypervisor will use "p" which >> will be the size of the natural pointer. > > For a 32-bit Xen the check would be that a guest was not inadvertently > violating this rule, such a guest would crash if it was run on a 64-bit > hypervisor (which would see the non-zero padding as part of the pointer), > by rejecting such cases on 32-bit Xen we avoid such guests becoming > established and therefore presenting a case for us to relax this rule in > one way or another. It would add overhead each time we want to copy to/from the guest memory. TBH, I don't think it's our business to check if the guest properly filling out the structure. It could happen only when the guest decides to implement it's own set_guest_handle_macro. As long as we don't crash the hypervisor it's fine. Regards, -- Julien Grall