On Wed, Sep 2, 2015 at 7:08 AM, Andy Lutomirski <l...@amacapital.net> wrote: > On Sep 2, 2015 2:51 AM, "Stas Sergeev" <s...@list.ru> wrote: >> >> https://lkml.org/lkml/2015/7/21/208 >> >> Guys, you gonna be kidding. >> Is this a new trend of breaking dosemu, or what? >> >>> VM86 is entirely broken if ptrace, syscall auditing, or >>> NOHZ_FULL is in use. The code is a big undocumented mess, it's >>> a real PITA to test, and it looks like a big chunk of vm86_32.c >> >> >> It is a CPU feature that kernel should support, and always >> did without any problems. If it started to have problems because >> of your actions, then you can as well fix your code. >> >> > No one should be using it anyway. Use DOSBOX or KVM instead. >> >> Have you done the benchmarks between dosbox and dosemu >> before saying that? Please do, thanks. (don't forget to include >> dosemu2 in your benchmarks too, as it outperforms both) > > I wasn't aware of your dosemu variant at the time, and I incorrectly > thought that dosemu was unmaintained. > > Does real mode performance matter any more? > >> >>> Let's accelerate its slow death. >> >> > > Dosemu is much less dead than I thought it was when I wrote that > patch. Sorry :( > >> >> > + Enabling this option adds considerable attack surface to the >> > + kernel and slows down system calls and exception handling. >> >> Yes, I realize that threatening people with the "considerable attack surface" >> is a good way to "accelerate its slow death", but please care to explain >> that attack surface, thankyou. > > The user_mode vs user_mode_vm thing was scary and contained at least > one real bug. That particular issue is gone now, though. > > Before Brian's cleanups, vm86 did horrible things to the entry asm, > the stack layout, and signal handling, and that scared me. That's > hopefully in much better shape now, though. > > The mark_screen_rdonly thing is still kind of scary. It changes PTEs > on arbitrary mappings behind the vm's back. > > I'd be amenable to switching the default back to y and perhaps adding > a sysctl to make the distros more comfortable. Ingo, Kees, Brian, > what do you think?
Yeah, I think putting this under distro control (and user control) is the best option here. -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
