Messages in this thread | | | Date | Fri, 14 Oct 2011 22:39:40 +0200 | Subject | Re: [RFC] fixing the UML failure root cause | From | richard -rw- weinberger <> |
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On Fri, Oct 14, 2011 at 10:31 PM, Andrew Lutomirski <luto@mit.edu> wrote: > On Fri, Oct 14, 2011 at 1:23 PM, richard -rw- weinberger > <richard.weinberger@gmail.com> wrote: >> On Fri, Oct 14, 2011 at 10:17 PM, Andrew Lutomirski <luto@mit.edu> wrote: >>> On Fri, Oct 14, 2011 at 12:53 PM, richard -rw- weinberger >>> <richard.weinberger@gmail.com> wrote: >>>> On Tue, Oct 11, 2011 at 7:24 PM, Andrew Lutomirski <luto@mit.edu> wrote: >>>>> What do you think of this approach? If it seems good, I'll finish the >>>>> patch and submit it. >>>>> >>>>> With this patch applied, UML appears to work, but it fills the log with >>>>> exploit attempt warnings. Any ideas on what to do about that? >>>>> >>>> >>>> I can confirm that this patch works. >>>> And I really like vsyscall=emulate because with that UML can trap vsyscalls. :-) >>> >>> Are you sure you don't mean vsyscall=native? I suspect that UML can't >>> actually trap vsyscalls in emulate mode right now, although that ought >>> to be fixable. >>> >> >> Doesn't vsyscall_emu_64.S transform any vsyscall into a real syscall? >> So UML can trap it. > > Only if that code actually executes. In vsyscall=emulate mode, the > page is not executable and a trap is taken instead. It's not entirely > clear what the right thing to do is wrt ptrace users.
Okay. I did some tests, in vsyscall=emulate mode a statically linked program reports always the correct time. On < 3.1 kernel this was not the case, here the same program reports always the hosts time...
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