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? /Jarkko
