On Wed, 2022-04-13 at 14:10 -0700, Reinette Chatre wrote: > In the initial (SGX1) version of SGX, pages in an enclave need to be > created with permissions that support all usages of the pages, from the > time the enclave is initialized until it is unloaded. For example, > pages used by a JIT compiler or when code needs to otherwise be > relocated need to always have RWX permissions. > > SGX2 includes a new function ENCLS[EMODPR] that is run from the kernel > and can be used to restrict the EPCM permissions of regular enclave > pages within an initialized enclave. > > Introduce ioctl() SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS to support > restricting EPCM permissions. With this ioctl() the user specifies > a page range and the EPCM permissions to be applied to all pages in > the provided range. ENCLS[EMODPR] is run to restrict the EPCM > permissions followed by the ENCLS[ETRACK] flow that will ensure > no cached linear-to-physical address mappings to the changed > pages remain. > > It is possible for the permission change request to fail on any > page within the provided range, either with an error encountered > by the kernel or by the SGX hardware while running > ENCLS[EMODPR]. To support partial success the ioctl() returns an > error code based on failures encountered by the kernel as well > as two result output parameters: one for the number of pages > that were successfully changed and one for the SGX return code. > > The page table entry permissions are not impacted by the EPCM > permission changes. VMAs and PTEs will continue to allow the > maximum vetted permissions determined at the time the pages > are added to the enclave. The SGX error code in a page fault > will indicate if it was an EPCM permission check that prevented > an access attempt. > > No checking is done to ensure that the permissions are actually > being restricted. This is because the enclave may have relaxed > the EPCM permissions from within the enclave without the kernel > knowing. An attempt to relax permissions using this call will > be ignored by the hardware. > > Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx> Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx> BR, Jarkko
