> On Dec 11, 2018, at 8:52 AM, Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > >> On Tue, Dec 11, 2018 at 07:41:27AM -0800, Andy Lutomirski wrote: >> >> >>>> On Dec 10, 2018, at 3:24 PM, Josh Triplett <josh@xxxxxxxxxxxxxxxx> wrote: >>>> >>>> On Mon, Dec 10, 2018 at 03:21:37PM -0800, Sean Christopherson wrote: >>>> At that point I realized it's a hell of a lot easier to simply provide >>>> an IOCTL via /dev/sgx that allows userspace to register a per-process >>>> ENCLU exception handler. At a high level, the basic idea is the same >>>> as the vDSO approach: provide a hardcoded fixup handler for ENCLU and >>>> attempt to fixup select unhandled exceptions that occurred in user code. >>> >>> So, on the one hand, this is *absolutely* much cleaner than the VDSO >>> approach. On the other hand, this is global process state and has some >>> of the same problems as a signal handler as a result. >> >> I liked the old version better for this reason > > This isn't fundamentally different than forcing all EENTER calls through > the vDSO, which is also per-process. Technically this is more flexible > in that regard since userspace gets to choose where their one ENCLU gets > to reside. Userspace can have per-enclave entry flows so long as the > actual ENLU[EENTER] is common, same as vDSO. Right. The problem is that user libraries have a remarkably hard time agreeing on where their one copy of anything lives. > >> and for another reason: >> while this new one looks very very simple, it still has the hidden >> complexity that the magic values written to registers in the event of an >> exception are very much Linux specific. > > Definitely more magical, but not necessarily more difficult to document. > It'd essentially be an extension of hardware's AEE/AEP behavior. > >> OTOH, the old approach clobbered more regs than needed, but that’s a easy fix.
