[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC 02/19] xen: guestcopy: Provide an helper to copy string from guest
>>> On 18.06.14 at 14:22, <julien.grall@xxxxxxxxxx> wrote: > On 06/18/2014 12:59 PM, Jan Beulich wrote: >>>>> On 18.06.14 at 00:43, <dgdegra@xxxxxxxxxxxxx> 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, <julien.grall@xxxxxxxxxx> wrote: >>>>>> On 17/06/14 09:01, Jan Beulich wrote: >>>>>>>>>> On 16.06.14 at 18:17, <julien.grall@xxxxxxxxxx> 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. But just to make sure - the generic helper introduced there shouldn't behave that way if being given the proposed name. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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