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. > > 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. BR, Jarkko
