From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [RFC 02/19] xen: guestcopy: Provide an helper to copy string from guest Date: Wed, 18 Jun 2014 13:22:32 +0100 Message-ID: <53A18488.1030305@linaro.org> References: <1402935486-29136-1-git-send-email-julien.grall@linaro.org> <1402935486-29136-3-git-send-email-julien.grall@linaro.org> <53A011E4020000780001ADF4@mail.emea.novell.com> <53A005AC.3060306@linaro.org> <53A023E7020000780001AE8B@mail.emea.novell.com> <53A00903.2060904@linaro.org> <53A0C482.1090309@tycho.nsa.gov> <53A19B39020000780001B53A@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta4.messagelabs.com ([85.158.143.247]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1WxEsv-0005UG-0d for xen-devel@lists.xenproject.org; Wed, 18 Jun 2014 12:22:37 +0000 Received: by mail-wi0-f169.google.com with SMTP id hi2so8383668wib.2 for ; Wed, 18 Jun 2014 05:22:35 -0700 (PDT) In-Reply-To: <53A19B39020000780001B53A@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 , Daniel De Graaf Cc: Keir Fraser , ian.campbell@citrix.com, tim@xen.org, Ian Jackson , stefano.stabellini@citrix.com, xen-devel@lists.xenproject.org List-Id: xen-devel@lists.xenproject.org On 06/18/2014 12:59 PM, Jan Beulich wrote: >>>> On 18.06.14 at 00:43, wrote: >> On 06/17/2014 05:23 AM, Julien Grall wrote: >>> >>> >>> On 17/06/14 10:17, Jan Beulich wrote: >>>>>>> On 17.06.14 at 11:09, wrote: >>>>> On 17/06/14 09:01, Jan Beulich wrote: >>>>>>>>> On 16.06.14 at 18:17, wrote: >>>>>>> + >>>>>>> + /* Add an extra +1 to append \0. We can't assume the guest will >>>>>>> + * provide a valid string */ >>>>>> >>>>>> Now this is the case for flask, but for a generic string copying >>>>>> routine I don't think this is desirable. It seems especially wrong to >>>>>> aid the guest with putting a NUL where none was. If you really >>>>>> want this, I guess you would be better off adding two variants: >>>>>> One which demands the string to be NUL-terminated (in which >>>>>> case passing in a size is sort of bogus), and one which takes a >>>>>> size and inserts a NUL. >> >> I'm not sure why you would want a string copy-in function to not >> NUL-terminate the strings it copies in. If you don't want the strings >> to be NUL-terminated at all, I would call it buffer copy-in function >> (and copy_from_guest seems to cover buffer copy-in better). If you want >> the strings to be NUL-terminated and the guest has passed you a length, >> it's simpler to have the hypervisor add the NUL instead of copying it >> and then checking that it is there. The current toolstack code for >> XSM/FLASK relies on the hypervisor to add the NUL terminator, since it >> often passes in (s, strlen(s)). > > I didn't say to just leave such strings unterminated. Instead I said > that if there is no zero terminator, rather than putting one there we > should just fail the operation if the buffer size limit was exceeded. It looks like I use the same trick as for flask, i.e using strlen(s) and therefore let the hypervisor set the NUL-terminator. I will add a comment on this function to say that we expect the hypervisor to set the NUL-terminator. Regards, -- Julien Grall