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Re: [PATCH 26/26] x86, pkeys: Documentation

From	Ingo Molnar <mingo@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 26/26] x86, pkeys: Documentation
Date	2015-09-24 12:00 +0200
Message-ID	<qcbtN-7ST-37@gated-at.bofh.it> (permalink)
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* Dave Hansen <dave@sr71.net> wrote:

> > Another question, related to enumeration as well: I'm wondering whether 
> > there's any way for the kernel to allocate a bit or two for its own purposes - 
> > such as protecting crypto keys? Or is the facility fundamentally intended for 
> > user-space use only?
> 
> No, that's not possible with the current setup.

Ok, then another question, have you considered the following usecase:

AFAICS pkeys only affect data loads and stores. Instruction fetches are notably 
absent from the documentation. Can you clarify that instructions can be fetched 
and executed from PTE_READ but pkeys-all-access-disabled pags?

If yes then this could be a significant security feature / usecase for pkeys: 
executable sections of shared libraries and binaries could be mapped with pkey 
access disabled. If I read the Intel documentation correctly then that should be 
possible.

The advantage of doing that is that an existing attack method to circumvent ASLR 
(or to scout out an unknown binary) is to use an existing (user-space) information 
leak to read the address space of a server process - and to use that to figure out 
the actual code present at that address.

The code signature can then be be used to identify the precise layout of the 
binary, and/or to create ROP gadgets - to escallate permissions using an otherwise 
not exploitable buffer overflow.

I.e. AFAICS pkeys could be used to create true '--x' permissions for executable 
(user-space) pages.

But I might be reading it wrong ...

Thanks,

	Ingo
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Re: [PATCH 26/26] x86, pkeys: Documentation Ingo Molnar <mingo@kernel.org> - 2015-09-24 12:00 +0200
  Re: [PATCH 26/26] x86, pkeys: Documentation Andy Lutomirski <luto@amacapital.net> - 2015-09-24 21:20 +0200
    Re: [PATCH 26/26] x86, pkeys: Documentation Ingo Molnar <mingo@kernel.org> - 2015-09-25 09:20 +0200
  Re: [PATCH 26/26] x86, pkeys: Documentation Dave Hansen <dave@sr71.net> - 2015-09-24 21:20 +0200
    Re: [PATCH 26/26] x86, pkeys: Documentation Ingo Molnar <mingo@kernel.org> - 2015-09-25 08:20 +0200
    Re: [PATCH 26/26] x86, pkeys: Documentation Ingo Molnar <mingo@kernel.org> - 2015-10-01 13:20 +0200
      Re: [PATCH 26/26] x86, pkeys: Documentation Kees Cook <keescook@google.com> - 2015-10-01 22:40 +0200
        Re: [PATCH 26/26] x86, pkeys: Documentation Andy Lutomirski <luto@amacapital.net> - 2015-10-01 22:50 +0200
          Re: [PATCH 26/26] x86, pkeys: Documentation Ingo Molnar <mingo@kernel.org> - 2015-10-02 08:30 +0200
            Re: [PATCH 26/26] x86, pkeys: Documentation Dave Hansen <dave@sr71.net> - 2015-10-02 20:00 +0200
              Re: [PATCH 26/26] x86, pkeys: Documentation Ingo Molnar <mingo@kernel.org> - 2015-10-03 09:30 +0200
        Re: [PATCH 26/26] x86, pkeys: Documentation Dave Hansen <dave@sr71.net> - 2015-10-01 23:00 +0200
        Re: [PATCH 26/26] x86, pkeys: Documentation Dave Hansen <dave@sr71.net> - 2015-10-02 00:40 +0200
        Re: [PATCH 26/26] x86, pkeys: Documentation Dave Hansen <dave@sr71.net> - 2015-10-02 00:40 +0200
          Re: [PATCH 26/26] x86, pkeys: Documentation Kees Cook <keescook@google.com> - 2015-10-02 00:40 +0200
          Re: [PATCH 26/26] x86, pkeys: Documentation Linus Torvalds <torvalds@linux-foundation.org> - 2015-10-02 00:50 +0200
            Re: [PATCH 26/26] x86, pkeys: Documentation Dave Hansen <dave@sr71.net> - 2015-10-02 01:00 +0200
              Re: [PATCH 26/26] x86, pkeys: Documentation Linus Torvalds <torvalds@linux-foundation.org> - 2015-10-02 03:40 +0200
                Re: [PATCH 26/26] x86, pkeys: Documentation Dave Hansen <dave@sr71.net> - 2015-10-02 20:10 +0200
            Re: [PATCH 26/26] x86, pkeys: Documentation Ingo Molnar <mingo@kernel.org> - 2015-10-02 09:10 +0200
              Re: [PATCH 26/26] x86, pkeys: Documentation Ingo Molnar <mingo@kernel.org> - 2015-10-03 09:00 +0200
            Re: [PATCH 26/26] x86, pkeys: Documentation Paolo Bonzini <pbonzini@redhat.com> - 2015-10-02 13:50 +0200
              Re: [PATCH 26/26] x86, pkeys: Documentation Linus Torvalds <torvalds@linux-foundation.org> - 2015-10-02 14:00 +0200
                Re: [PATCH 26/26] x86, pkeys: Documentation Paolo Bonzini <pbonzini@redhat.com> - 2015-10-02 14:20 +0200
                Re: [PATCH 26/26] x86, pkeys: Documentation Ingo Molnar <mingo@kernel.org> - 2015-10-03 08:50 +0200
          Re: [PATCH 26/26] x86, pkeys: Documentation Andy Lutomirski <luto@amacapital.net> - 2015-10-02 01:00 +0200
          Re: [PATCH 26/26] x86, pkeys: Documentation Ingo Molnar <mingo@kernel.org> - 2015-10-02 08:10 +0200
  Re: [PATCH 26/26] x86, pkeys: Documentation Ingo Molnar <mingo@kernel.org> - 2015-10-03 10:20 +0200

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