Re: RFC: userspace exception fixups

[Dave Hansen]

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.

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.