On Fri, Jan 05, 2018 at 10:01:23AM -0800, Andy Lutomirski wrote: > Yes. There are very clever tools like 'pin' that instrument a binary > by decoding all the instructions it executes and generating an > instrumented copy. If that binary calls into the vDSO, the vDSO gets > decoded and instrumented (which works fine). If the binary calls into > the vsyscall page, it still needs to work. So the vsyscall page > contains machine code that actually works (even if it's NX) to support > these tools. The authors and users of the tools yelled loudly in an > earlier version of the vsyscall emulation code that didn't support > this use case.
It rings a bell... > The root cause here is that 4.4 is KAISER, not KPTI. The > kaiser_set_shadow_pgd() function is a steaming pile of shit, and this > is a known bug in it. Tell me about it. We found out last night it breaks EFI too, see: https://lkml.kernel.org/r/[email protected] To put it mildly, this new PTI et al crap will bring us a lot of fun in the coming year. I tell ya, a year from now we'll be dealing with the fallout from this. > I have zero desire to hack up some stupid special case in there. For > the modern KPTI kernels, I rewrote that function entirely to be much > simpler and much more correct. > > It should be straightforward to kludge something up, though, but I'm > not volunteering. Yeah, I think adding _PAGE_RW into the mix should fix it but I need to give it a try first. Thanks for the test! -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.
