On Fri, Nov 02, 2018 at 10:13:23AM -0700, Dave Hansen wrote: > On 11/2/18 10:06 AM, Sean Christopherson wrote: > > On Fri, Nov 02, 2018 at 09:56:44AM -0700, Dave Hansen wrote: > >> On 11/2/18 9:30 AM, Sean Christopherson wrote: > >>> What if rather than having userspace register an address for fixup, the > >>> kernel instead unconditionally does fixup on the ENCLU opcode? > >> > >> The problem is knowing what to do for the fixup. If we have a simple > >> action to take that's universal, like backing up %RIP, or setting some > >> other register state, it's not bad. > > > > Isn't the EENTER/RESUME behavior universal? Or am I missing something? > > Could someone write down all the ways we get in and out of the enclave? > > I think we always get in from userspace calling EENTER or ERESUME. We > can't ever enter directly from the kernel, like via an IRET from what I > understand. Correct, the only way to get into the enclave is EENTER or ERESUME. My understanding is that even SMIs bounce through the AEX target before transitioning to SMM. > We get *out* from exceptions, hardware interrupts, or enclave-explicit > EEXITs. Did I miss any? Remind me where the hardware lands the control > flow in each of those exit cases. And VMExits. There are basically two cases: EEXIT and everything else. EEXIT is a glorified indirect jump, e.g. %RBX holds the target %RIP. Everything else is an Asynchronous Enclave Exit (AEX). On an AEX, %RIP is set to a value specified by EENTER/ERESUME, %RBP and %RSP are restored to pre-enclave values and all other registers are loaded with synthetic state. The actual interrupt/exception/VMExit then triggers, e.g. the %RIP on the stack for an exception is always the AEX target, not the %RIP inside the enclave that actually faulted.
