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Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location

From Ingo Molnar <mingo@kernel.org>
Newsgroups linux.kernel
Subject Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location
Date 2017-01-06 08:00 +0100
Message-ID <sWwFj-693-1@gated-at.bofh.it> (permalink)
References (4 earlier) <sWlJT-7ej-21@gated-at.bofh.it> <sWmFY-7Qg-23@gated-at.bofh.it> <sWnsm-8rY-39@gated-at.bofh.it> <sWnLH-83-15@gated-at.bofh.it> <sWoeK-ic-15@gated-at.bofh.it>
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* Thomas Garnier <thgarnie@google.com> wrote:

> >> Not sure I fully understood and I don't want to miss an important point. Do 
> >> you mean making GDT (remapping and per-cpu) read-only and switch the 
> >> writeable flag only when we write to the per-cpu entry?
> >
> > What I mean is: write to the GDT through normal percpu access (or whatever the 
> > normal mapping is) but load a read-only alias into the GDT register.  As long 
> > as nothing ever tries to write through the GDTR alias, no page faults will be 
> > generated.  So we just need to make sure that nothing ever writes to it 
> > through GDTR.  AFAIK the only reason the CPU ever writes to the address in 
> > GDTR is to set an accessed bit.
> 
> A write is made when we use load_TR_desc (ltr). I didn't see any other yet.

Is this write to the GDT, generated by the LTR instruction, done unconditionally 
by the hardware?

Thanks,

	Ingo

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Thread

[RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-04 23:20 +0100
  Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Ingo Molnar <mingo@kernel.org> - 2017-01-05 09:30 +0100
    Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Arjan van de Ven <arjan@linux.intel.com> - 2017-01-05 16:10 +0100
      Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-05 17:50 +0100
        Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Arjan van de Ven <arjan@linux.intel.com> - 2017-01-05 20:10 +0100
          Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-05 20:10 +0100
        Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Borislav Petkov <bp@alien8.de> - 2017-01-06 18:50 +0100
          Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-06 19:10 +0100
    Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-05 17:40 +0100
      Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Ingo Molnar <mingo@kernel.org> - 2017-01-06 07:40 +0100
  Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-05 19:20 +0100
    Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Andy Lutomirski <luto@amacapital.net> - 2017-01-05 19:40 +0100
      Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-05 19:40 +0100
    Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Arjan van de Ven <arjan@linux.intel.com> - 2017-01-05 20:10 +0100
      Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-05 20:20 +0100
        Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Andy Lutomirski <luto@kernel.org> - 2017-01-05 21:20 +0100
          Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-05 22:10 +0100
            Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Andy Lutomirski <luto@amacapital.net> - 2017-01-05 22:30 +0100
              Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-05 23:00 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Ingo Molnar <mingo@kernel.org> - 2017-01-06 08:00 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-06 19:10 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Andy Lutomirski <luto@kernel.org> - 2017-01-06 23:30 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-07 00:00 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Andy Lutomirski <luto@kernel.org> - 2017-01-07 00:40 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Ingo Molnar <mingo@kernel.org> - 2017-01-07 08:50 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Andy Lutomirski <luto@amacapital.net> - 2017-01-07 17:00 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Ingo Molnar <mingo@kernel.org> - 2017-01-07 08:40 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Andy Lutomirski <luto@amacapital.net> - 2017-01-07 17:10 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-09 23:40 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Ingo Molnar <mingo@kernel.org> - 2017-01-10 11:30 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-10 18:20 +0100
          Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Linus Torvalds <torvalds@linux-foundation.org> - 2017-01-06 00:10 +0100
            Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-06 00:30 +0100
            Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Andy Lutomirski <luto@amacapital.net> - 2017-01-06 03:40 +0100
              Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Thomas Garnier <thgarnie@google.com> - 2017-01-06 19:10 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Andy Lutomirski <luto@kernel.org> - 2017-01-06 23:00 +0100
                Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Ingo Molnar <mingo@kernel.org> - 2017-01-07 08:50 +0100
      Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Ingo Molnar <mingo@kernel.org> - 2017-01-06 07:50 +0100
  Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location Andy Lutomirski <luto@amacapital.net> - 2017-01-05 19:30 +0100

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