On 1/15/21 6:07 AM, Kai Huang wrote: >>From virtual EPC's perspective, if we don't force this in kernel, then > *theoretically*, userspace can use fork() to make multiple VMs map to the > same physical EPC, which will potentially cause enclaves in all VMs to behave > abnormally. So to me, from this perspective, it's better to enforce in kernel > so that only first VM can use this virtual EPC instance, because EPC by > architectural design cannot be shared. > > But as Sean said, KVM doesn't support VM across multiple mm structs. And if I > read code correctly, KVM doesn't support userspace to use fork() to create new > VM. For instance, when creating VM, KVM grabs current->mm and keeps it in > 'struct kvm' for bookkeeping, and kvm_vcpu_ioctl() and kvm_device_ioctl() will > refuse to work if kvm->mm doesn't equal to current->mm. So in practice, I > believe w/o enforcing this in kernel, we should also have no problem here. > > Sean, please correct me if I am wrong. > > Dave, if above stands, do you think it is reasonable to keep current->mm in > epc->mm and enforce in sgx_virt_epc_mmap()? Everything you wrote above tells me the kernel should not be enforcing the behavior. You basically said that it's only a theoretical problem, and old if someone goes and does something with KVM that's nobody can do today. You've 100% convinced me that having the kernel enforce this is *un*reasonable.
