On Tue, Dec 11, 2018 at 09:58:19AM -0800, Andy Lutomirski wrote: > > 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. Are you concerned about userspace shooting themselves in the foot, e.g. unknowingly overwriting their handler? Requiring unregister->register to change the handler would mitigate that issue for the most part. Or we could even say it's a write-once property. That obviously doesn't solve the issue of a userspace application deliberately using two different libraries to run enclaves in a single process, but I have a hard time envisioning a scenario where someone would want to use two different *SGX* libraries in a single process. Don't most of the signal issue arise due to loading multiple libraries that provide *different* services needing to handle signals?
