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Message-ID: <55E76FCB.7090304@list.ru> Date: Thu, 3 Sep 2015 00:53:15 +0300 From: Stas Sergeev <stsp@...t.ru> To: Andy Lutomirski <luto@...capital.net> Cc: Josh Boyer <jwboyer@...oraproject.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Andrew Bird (Sphere Systems)" <ajb@...eresystems.co.uk>, Linus Torvalds <torvalds@...ux-foundation.org>, Ingo Molnar <mingo@...nel.org>, Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com> Subject: Re: stop breaking dosemu (Re: x86/kconfig/32: Rename CONFIG_VM86 and default it to 'n') 03.09.2015 00:40, Andy Lutomirski пишет: > On Wed, Sep 2, 2015 at 2:12 PM, Stas Sergeev <stsp@...t.ru> wrote: >> 02.09.2015 23:55, Andy Lutomirski пишет: >> >>> On Wed, Sep 2, 2015 at 1:47 PM, Stas Sergeev <stsp@...t.ru> wrote: >>>> 02.09.2015 23:22, Josh Boyer пишет: >>>>> On Wed, Sep 2, 2015 at 1:50 PM, Stas Sergeev <stsp@...t.ru> wrote: >>>>>> 02.09.2015 20:46, Josh Boyer пишет: >>>>>>> On Wed, Sep 2, 2015 at 10:08 AM, Andy Lutomirski <luto@...capital.net> >>>>>>> wrote: >>>>>>>> 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? >>>>>>> Can you please leave the default as N, and have a sysctl option to >>>>>>> enable it instead? While dosemu might still be in use, it isn't going >>>>>>> to be the common case at all. So from a distro perspective, I think >>>>>>> we'd probably rather have the default match the common case. >>>>>> The fact that fedora doesn't package dosemu, doesn't automatically >>>>>> mean all other distros do not too. Since when kernel defaults should >>>>>> match the ones of fedora? >>>>> I didn't say that. >>>> What you said was: >>>> --- >>>> >>>> While dosemu might still be in use, it isn't going >>>> to be the common case at all. So from a distro perspective >>>> >>>> --- >>>> ... which is likely true only in fedora circe. >>>> >>>>> The default right now is N. >>>> In a not yet released kernel, unless I am mistaken. >>>> If fedora already provides that kernel, other distros likely not. >>>> >>>>> I asked it be left >>>>> that way. That's all. >>>> Lets assume its not yet N, unless there was a kernel release already. >>>> Its easy to get back if its not too late. >>> How about CONFIG_SYSCTL_VM86_DEFAULT which defaults to Y? Fedora >>> could set it to N. >> Sorry, I don't understand this sysctl proposal. >> Could you please educate me what is it all about? >> This sysctl will disable or enable the vm86() syscall at run-time, >> right? What does it give us? If you disable something in the >> config, this gives you, say, smaller kernel image. If OTOH you >> add the run-time switch, it gives you a bigger image, regardless >> of its default value. >> I might be missing something, but I don't understand what >> problem will this solve? Have I missed some earlier message >> in this thread? > For the 99%+ of users who don't use dosemu, it prevents exploits that > target vm86 from attacking their kernel. I don't think the attack scenario was satisfactory explained. IIRC you only said that --- The mark_screen_rdonly thing is still kind of scary. It changes PTEs on arbitrary mappings behind the vm's back. --- Just go ahead and remove mark_screen_rdonly, big deal. Is this all of the threat? Or do we treat _every_ syscall as the potential attack target? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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