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. > 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.
