On Tue, Dec 11, 2018 at 03:10:52PM -0800, Andy Lutomirski wrote: > On Tue, Dec 11, 2018 at 2:23 PM Sean Christopherson > <sean.j.christopherson@xxxxxxxxx> wrote: > > > > 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? > > I can easily imagine two SGX libraries that know nothing about each > other running in the same process. One or both could be PKCS#11 > modules, for example. Argh, wasn't thinking about loading other libraries that would also be using SGX.
