On Wed, Jan 12, 2022 at 6:56 PM Jarkko Sakkinen <jarkko@xxxxxxxxxx> wrote: > > On Thu, Jan 13, 2022 at 01:50:13AM +0200, Jarkko Sakkinen wrote: > > On Tue, Jan 11, 2022 at 09:13:27AM -0800, Reinette Chatre wrote: > > > Hi Jarkko, > > > > > > On 1/10/2022 5:53 PM, Jarkko Sakkinen wrote: > > > > On Mon, Jan 10, 2022 at 04:05:21PM -0600, Haitao Huang wrote: > > > >> On Sat, 08 Jan 2022 10:22:30 -0600, Jarkko Sakkinen <jarkko@xxxxxxxxxx> > > > >> wrote: > > > >> > > > >>> On Sat, Jan 08, 2022 at 05:51:46PM +0200, Jarkko Sakkinen wrote: > > > >>>> On Sat, Jan 08, 2022 at 05:45:44PM +0200, Jarkko Sakkinen wrote: > > > >>>>> On Fri, Jan 07, 2022 at 10:14:29AM -0600, Haitao Huang wrote: > > > >>>>>>>>> OK, so the question is: do we need both or would a > > > >>>> mechanism just > > > >>>>>>>> to extend > > > >>>>>>>>> permissions be sufficient? > > > >>>>>>>> > > > >>>>>>>> I do believe that we need both in order to support pages > > > >>>> having only > > > >>>>>>>> the permissions required to support their intended use > > > >>>> during the > > > >>>>>>>> time the > > > >>>>>>>> particular access is required. While technically it is > > > >>>> possible to grant > > > >>>>>>>> pages all permissions they may need during their lifetime it > > > >>>> is safer to > > > >>>>>>>> remove permissions when no longer required. > > > >>>>>>> > > > >>>>>>> So if we imagine a run-time: how EMODPR would be useful, and > > > >>>> how using it > > > >>>>>>> would make things safer? > > > >>>>>>> > > > >>>>>> In scenarios of JIT compilers, once code is generated into RW pages, > > > >>>>>> modifying both PTE and EPCM permissions to RX would be a good > > > >>>> defensive > > > >>>>>> measure. In that case, EMODPR is useful. > > > >>>>> > > > >>>>> What is the exact threat we are talking about? > > > >>>> > > > >>>> To add: it should be *significantly* critical thread, given that not > > > >>>> supporting only EAUG would leave us only one complex call pattern with > > > >>>> EACCEPT involvement. > > > >>>> > > > >>>> I'd even go to suggest to leave EMODPR out of the patch set, and > > > >>>> introduce > > > >>>> it when there is PoC code for any of the existing run-time that > > > >>>> demonstrates the demand for it. Right now this way too speculative. > > > >>>> > > > >>>> Supporting EMODPE is IMHO by factors more critical. > > > >>> > > > >>> At least it does not protected against enclave code because an enclave > > > >>> can > > > >>> always choose not to EACCEPT any of the EMODPR requests. I'm not only > > > >>> confused here about the actual threat but also the potential adversary > > > >>> and > > > >>> target. > > > >>> > > > >> I'm not sure I follow your thoughts here. The sequence should be for enclave > > > >> to request EMODPR in the first place through runtime to kernel, then to > > > >> verify with EACCEPT that the OS indeed has done EMODPR. > > > >> If enclave does not verify with EACCEPT, then its own code has > > > >> vulnerability. But this does not justify OS not providing the mechanism to > > > >> request EMODPR. > > > > > > > > The question is really simple: what is the threat scenario? In order to use > > > > the word "vulnerability", you would need one. > > > > > > > > Given the complexity of the whole dance with EMODPR it is mandatory to have > > > > one, in order to ack it to the mainline. > > > > > > > > > > Which complexity related to EMODPR are you concerned about? In a later message > > > you mention "This leaves only EAUG and EMODT requiring the EACCEPT handshake" > > > so it seems that you are perhaps concerned about the flow involving EACCEPT? > > > The OS does not require nor depend on EACCEPT being called as part of these flows > > > so a faulty or misbehaving user space omitting an EACCEPT call would not impact > > > these flows in the OS, but would of course impact the enclave. > > > > I'd say *any* complexity because I see no benefit of supporting it. E.g. > > EMODPR/EACCEPT/EMODPE sequence I mentioned to Haitao concerns me. How is > > EMODPR going to help with any sort of workload? > > I've even started think should we just always allow mmap()? I suspect this may be the most ergonomic way forward. Instructions like EAUG/EMODPR/etc are really irrelevant implementation details to what the enclave wants, which is a memory mapping in the enclave. Why make the enclave runner do multiple context switches just to change the memory map of an enclave? > The worst thing > that can happen is that the enclave crashes. Does that matter all that > much? I'm asking because access control is the main theme in SGX2 patch set > that IMHO should be considered to the ground. It really "stress tests" that > area. If we can settle on that, then other things are just technical details > that we can surely sort out. > > /Jarkko
