On Thu, Mar 17, 2022 at 11:50:41PM +0200, Jarkko Sakkinen wrote: > On Thu, Mar 17, 2022 at 09:28:45AM -0500, Haitao Huang wrote: > > Hi > > > > On Thu, 17 Mar 2022 02:11:28 -0500, Jarkko Sakkinen <jarkko@xxxxxxxxxx> > > wrote: > > > > > On Thu, Mar 17, 2022 at 09:01:07AM +0200, Jarkko Sakkinen wrote: > > > > On Mon, Mar 14, 2022 at 10:39:36AM -0500, Haitao Huang wrote: > > > > > Hi Jarkko > > > > > > > > > > On Sun, 13 Mar 2022 21:58:51 -0500, Jarkko Sakkinen > > > > <jarkko@xxxxxxxxxx> > > > > > wrote: > > > > > > > > > > > On Mon, Mar 14, 2022 at 04:50:56AM +0200, Jarkko Sakkinen wrote: > > > > > > > On Mon, Mar 14, 2022 at 04:49:37AM +0200, Jarkko Sakkinen wrote: > > > > > > > > On Fri, Mar 11, 2022 at 09:53:29AM -0800, Reinette Chatre wrote: > > > > > > > > > > > > > > > > > I saw Haitao's note that EMODPE requires "Read access > > > > permitted > > > > > > > by enclave". > > > > > > > > > This motivates that EMODPR->PROT_NONE should not be allowed > > > > > > > since it would > > > > > > > > > not be possible to relax permissions (run EMODPE) after that. > > > > > > > Even so, I > > > > > > > > > also found in the SDM that EACCEPT has the note "Read access > > > > > > > permitted > > > > > > > > > by enclave". That seems to indicate that EMODPR->PROT_NONE is > > > > > > > not practical > > > > > > > > > from that perspective either since the enclave will not be > > > > able to > > > > > > > > > EACCEPT the change. Does that match your understanding? > > > > > > > > > > > > > > > > Yes, PROT_NONE should not be allowed. > > > > > > > > > > > > > > > > This is however the real problem. > > > > > > > > > > > > > > > > The current kernel patch set has inconsistent API and EMODPR > > > > ioctl is > > > > > > > > simply unacceptable. It also requires more concurrency > > > > management > > > > > > > from > > > > > > > > user space run-time, which would be heck a lot easier to do > > > > in the > > > > > > > kernel. > > > > > > > > > > > > > > > > If you really want EMODPR as ioctl, then for consistencys sake, > > > > > > > then EAUG > > > > > > > > should be too. Like this when things go opposite directions, > > > > this > > > > > > > patch set > > > > > > > > plain and simply will not work out. > > > > > > > > > > > > > > > > I would pick EAUG's strategy from these two as it requires half > > > > > > > the back > > > > > > > > calls to host from an enclave. I.e. please combine > > > > mprotect() and > > > > > > > EMODPR, > > > > > > > > either in the #PF handler or as part of mprotect(), which ever > > > > > > > suits you > > > > > > > > best. > > > > > > > > > > > > > > > > I'll try demonstrate this with two examples. > > > > > > > > > > > > > > > > mmap() could go something like this() (simplified): > > > > > > > > 1. Execution #UD's to SYSCALL. > > > > > > > > 2. Host calls enclave's mmap() handler with mmap() parameters. > > > > > > > > 3. Enclave up-calls host's mmap(). > > > > > > > > 4. Loops the range with EACCEPTCOPY. > > > > > > > > > > > > > > > > mprotect() has to be done like this: > > > > > > > > 1. Execution #UD's to SYSCALL. > > > > > > > > 2. Host calls enclave's mprotect() handler. > > > > > > > > 3. Enclave up-calls host's mprotect(). > > > > > > > > 4. Enclave up-calls host's ioctl() to > > > > SGX_IOC_ENCLAVE_PERMISSIONS. > > > > > > > > > > I assume up-calls here are ocalls as we call them in our > > > > implementation, > > > > > which are the calls enclave make to untrusted side via EEXIT. > > > > >ar > > > > > If so, can your implementation combine this two up-calls into one, > > > > then host > > > > > side just do ioctl() and mprotect to kernel? If so, would that > > > > address your > > > > > concern about extra up-calls? > > > > > > > > > > > > > > > > > > 3. Loops the range with EACCEPT. > > > > > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > > > > 5. Loops the range with EACCEPT + EMODPE. > > > > > > > > > > > > > > > This is just terrible IMHO. I hope these examples bring some > > > > insight. > > > > > > > > > > > > E.g. in Enarx we have to add a special up-call (so called > > > > enarxcall in > > > > > > intermediate that we call sallyport, which provides shared buffer to > > > > > > communicate with the enclave) just for reseting the range with > > > > PROT_READ. > > > > > > Feel very redundant, adds ugly cruft and is completely opposite > > > > strategy > > > > > > to > > > > > > what you've chosen to do with EAUG, which is I think correct > > > > choice as > > > > > > far > > > > > > as API is concerned. > > > > > > > > > > The problem with EMODPR on #PF is that kernel needs to know what > > > > permissions > > > > > requested from enclave at the time of #PF. So enclave has to make > > > > at least > > > > > one call to kernel (again via ocall in our case, I assume up-call > > > > in your > > > > > case) to make the change. > > > > > > > > The #PF handler should do unconditionally EMODPR with PROT_READ. > > > > > > Or mprotect(), as long as secinfo contains PROT_READ. I don't care about > > > this detail hugely anymore because it does not affect uapi. > > > > > > Using EMODPR as a permission control mechanism is a ridiculous idea, and > > > I cannot commit to maintain a broken uapi. > > > > > > > Jarkko, how would automatically forcing PROT_READ on #PF work for this > > sequence? > > > > 1) EAUG a page (has to be RW) > > 2) EACCEPT(RW) > > 3) enclave copies some data to page > > 4) enclave wants to change permission to R > > > > If you are proposing mprotect, then as I indicated earlier, please address > > concerns raised by Reinette: > > https://lore.kernel.org/linux-sgx/e1c04077-0165-c5ec-53be-7fd732965e80@xxxxxxxxx/ > > For EAUG you can choose between #PF handler and having it as part of > mmap() with the same uapi. > > For EMODPR clearly #PF handler would be tricky but nothing prevents > resetting the permissions as part of mprotect() flow, which is trivial. > > One good reason to have a fixed EMODPR is that e.g. emulating properly > mprotect() is almost undoable if you don't do it otherwise. Specifically s/don't//g > the scenario where your address range spans through multiple adjacent > VMAs. It's even without EMODPR complex enough scenario that you really > don't want to ask yourself for more trouble than use EMODPR in a super > conservative manner. > > Having EMODPR fully exposed will only make more difficult API to do with > extra round-trips. If you want to use ring-0 instructions fully exposed, > please don't use a kernel. There's a bunch of hardware features in Intel > CPUs for which Linux does not provide 1:1 all wide open interfaces. > > BR, Jarkko
