Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging

From	Andy Lutomirski <luto@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging
Date	2017-05-26 09:30 +0200
Message-ID	<tLhR7-2UO-1@gated-at.bofh.it> (permalink)
References	<tL7I5-4wz-3@gated-at.bofh.it> <tLamB-6m2-1@gated-at.bofh.it> <tLbC1-79q-9@gated-at.bofh.it> <tLf2W-1ap-7@gated-at.bofh.it>
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On Thu, May 25, 2017 at 9:18 PM, Kevin Easton <kevin@guarana.org> wrote:
> (If it weren't for that, maybe you could point the last entry in the PML4
> at the PML4 itself, so it also works as a PML5 for accessing kernel
> addresses? And of course make sure nothing gets loaded above
> 0xffffff8000000000).

This was an old trick done for a very different reason: it lets you
find your page tables at virtual addresses that depend only on the VA
whose page table you're looking for and the top-level slot that points
back to itself.  IIRC Windows used to do this for its own memory
management purposes.  A major downside is that an arbitrary write
vulnerability lets you write your own PTEs without any guesswork.

--Andy

Thread

[PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-05-25 22:40 +0200
  [PATCHv1, RFC 2/8] x86/mm: Make virtual memory layout movable for CONFIG_X86_5LEVEL "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-05-25 22:40 +0200
  Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging Linus Torvalds <torvalds@linux-foundation.org> - 2017-05-26 01:30 +0200
    Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging Andy Lutomirski <luto@kernel.org> - 2017-05-26 02:50 +0200
      Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level  paging Kevin Easton <kevin@guarana.org> - 2017-05-26 06:30 +0200
        Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging Andy Lutomirski <luto@kernel.org> - 2017-05-26 09:30 +0200
    Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level  paging "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-05-26 15:10 +0200
      Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level  paging Andi Kleen <ak@linux.intel.com> - 2017-05-26 15:40 +0200
      Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging Linus Torvalds <torvalds@linux-foundation.org> - 2017-05-26 18:00 +0200
        Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level  paging "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-05-26 18:00 +0200
          Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging Linus Torvalds <torvalds@linux-foundation.org> - 2017-05-26 18:20 +0200
        Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level  paging Dave Hansen <dave.hansen@intel.com> - 2017-05-26 21:30 +0200
          Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging hpa@zytor.com - 2017-05-26 21:50 +0200
        Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging hpa@zytor.com - 2017-05-26 21:30 +0200
      Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging hpa@zytor.com - 2017-05-26 22:20 +0200

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