On Thu, Mar 10, 2022 at 12:33:20PM -0600, Haitao Huang wrote: > Hi Jarkko > > I have some trouble understanding the sequences below. > > On Thu, 10 Mar 2022 00:10:48 -0600, Jarkko Sakkinen <jarkko@xxxxxxxxxx> > wrote: > > > On Wed, Feb 23, 2022 at 07:21:50PM +0000, Dhanraj, Vijay wrote: > > > Hi All, > > > > > > Regarding the recent update of splitting the page permissions change > > > request into two IOCTLS (RELAX and RESTRICT), can we combine them into > > > one? That is, revert to how it was done in the v1 version? > > > > > > Why? Currently in Gramine (a library OS for unmodified applications, > > > https://gramineproject.io/) with the new proposed change, one needs to > > > store the page permission for each page or range of pages. And for every > > > request of `mmap` or `mprotect`, Gramine would have to do a lookup > > > of the > > > page permissions for the request range and then call the respective > > > IOCTL > > > either RESTRICT or RELAX. This seems a little overwhelming. > > > > > > Request: Instead, can we do `MODPE`, call `RESTRICT` IOCTL, and then do > > > an `EACCEPT` irrespective of RELAX or RESTRICT page permission request? > > > With this approach, we can avoid storing page permissions and simplify > > > the implementation. > > > > > > I understand RESTRICT IOCTL would do a `MODPR` and trigger `ETRACK` > > > flows > > > to do TLB shootdowns which might not be needed for RELAX IOCTL but I am > > > not sure what will be the performance impact. Is there any data point to > > > see the performance impact? > > > > > > Thanks, > > > -Vijay > > > > This should get better in the next versuin. "relax" is gone. And for > > dynamic EAUG'd pages only VMA and EPCM permissions matter, i.e. > > internal vm_max_prot_bits is set to RWX. > > > > I patched the existing series eno > > > > For Enarx I'm using the following patterns. > > > > Shim mmap() handler: > > 1. Ask host for mmap() syscall. > > 2. Construct secinfo matching the protection bits. > > 3. For each page in the address range: EACCEPTCOPY with a > > zero page. > > For EACCEPTCOPY to work, I believe PTE.RW is required for the target page. > So this only works for mmap(..., RW) or mmap(...,RWX). I use it only with EAUG. > So that gives you pages with RW/RWX. > > To change permissions of any of those pages from RW/RWX to R/RX , you need > call ENCLAVE_RESTRICT_PERMISSIONS ioctl with R or with PROT_NONE. you can't > just do EMODPE. > > so for RW->R, you either: > > 1)EMODPR(EPCM.NONE) > 2)EACCEPT(EPCM.NONE) > 3)EMODPE(R) -- not sure this would work as spec says EMODPE requires "Read > access permitted by enclave" > > or: > > 1)EMODPR(EPCM.PROT_R) > 2)EACCEPT(EPCM.PROT_R) I checked from SDM and you're correct. Then the appropriate thing is to reset to R. > > Shim mprotect() handler: > > 1. Ask host for mprotect() syscall. > > 2. For each page in the address range: EACCEPT with PROT_NONE > > secinfo and EMODPE with the secinfo having the prot bits. > > EACCEPT requires PTE.R. And EAUG'd pages will always initialized with > EPCM.RW, > so EACCEPT(EPCM.PROT_NONE) will fail with SGX_PAGE_ATTRIBUTES_MISMATCH. Ditto. > > Backend mprotect() handler: > > 1. Invoke ENCLAVE_RESTRICT_PERMISSIONS ioctl for the address > > range with PROT_NONE. > > 2. Invoke real mprotect() syscall. > > > Note #1 can only be done after EACCEPT. MODPR is not allowed for pending > pages. Yes, and that's what I'm doing. After that shim does EACCEPT's in a loop. Reinette, the ioctl should already check that either R or W is set in secinfo and return -EACCES. I.e. (* Check for misconfigured SECINFO flags*) IF ( (SCRATCH_SECINFO reserved fields are not zero ) or (SCRATCH_SECINFO.FLAGS.R is 0 and SCRATCH_SECINFO.FLAGS.W is not 0) ) THEN #GP(0); FI; I was testing this and wondering why my enclave #GP's, and then I checked SDM after reading Haitao's response. So clearly check in kernel side is needed. BR, Jarkko
