On Tue, Nov 20, 2018 at 12:11:33PM +0200, Jarkko Sakkinen wrote: > On Mon, Nov 19, 2018 at 09:00:08AM -0800, Andy Lutomirski wrote: > > On Mon, Nov 19, 2018 at 8:02 AM Jarkko Sakkinen > > <jarkko.sakkinen@xxxxxxxxxxxxxxx> wrote: > > > > > > On Mon, Nov 19, 2018 at 07:29:36AM -0800, Andy Lutomirski wrote: > > > > 1. The kernel needs some way to know *when* to apply this fixup. > > > > Decoding the instruction stream and doing it to all exceptions that > > > > hit an ENCLU instruction seems like a poor design. > > > > > > I'm not sure why you would ever need to do any type of fixup as the idea > > > is to just return to AEP i.e. from chosen exceptions (EPCM, #UD) the AEP > > > would work the same way as for exceptions that the kernel can deal with > > > except filling the exception information to registers. > > > > Sure, but how does the kernel know when to do that and when to send a > > signal? I don't really like decoding the instruction stream to figure > > it out. > > Hmm... why you have to decode instruction stream to find that out? Would > just depend on exception type (#GP with EPCM, #UD). Or are you saying > that kernel should need to SIGSEGV if there is in fact ENCLU so that > there is no infinite trap loop? Sorry, I'm a bit lost here that where > does this decoding requirement comes from in the first place. I > understand how it is used in Sean's proposal... > > Anyway, this option can be probably discarded without further > consideration because apparently single stepping can cause #DB SS fault > if AEP handler is anything else than a single instruction. > > For me it seems that by ruling out options, vDSO option is what is > left. I don't like it but at least it works... The section relevant in the SDM is 43.2.6 but I started to think that why in dumbed down return-to-AEP that would even be a problem? If you are single step debugging isn't that what you want? Continue single stepping in the AEP handler... I still don't understand the part where the need for decoding instruction stream comes in this dumbed down approach. There's not RIP manipulation or anything involved at all. With this reconsideration I would keep this as one option at least. /Jarkko
