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Re: [PATCH 26/34] mm: implement new mprotect_key() system call

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Hi Michael,

Thanks for all the comments!  I'll fix most of it when I post a new
version of the manpage, but I have a few general questions.

On 12/09/2015 03:08 AM, Michael Kerrisk (man-pages) wrote:
>>
>> +is the protection or storage key to assign to the memory.
> 
> Why "protection or storage key" here? This phrasing seems a
> little ambiguous to me, given that we also have a 'prot'
> argument.  I think it would be clearer just to say 
> "protection key". But maybe I'm missing something.

x86 calls it a "protection key" while powerpc calls it a "storage key".
 They're called "protection keys" consistently inside the kernel.

Should we just stick to one name in the manpages?

> * A general overview of why this functionality is useful.

Any preference on a central spot to do the general overview?  Does it go
in one of the manpages I'm already modifying, or a new one?

> * A note on which architectures support/will support
>   this functionality.

x86 only for now.  We might get powerpc support down the road somewhere.

> * Explanation of what a protection domain is.

A protection domain is a unique view of memory and is represented by the
value in the PKRU register.

> * Explanation of how a process (thread?) changes its
>   protection domain.

Changing protection domains is done by pkey_set() system call, or by
using the WRPKRU instruction.  The system call is preferred and less
error-prone since it enforces that a protection is allocated before its
access protection can be modified.

> * Explanation of the relationship between page permission
>   bits (PROT_READ/PROT_WRITE/PROTE_EXEC) and 
>   PKEY_DISABLE_ACCESS and PKEY_DISABLE_WRITE.
>   It's still not clear to me. Do the PKEY_* bits
>   override the PROT_* bits. Or, something else?

Protection keys add access restrictions in addition to existing page
permissions.  They can only take away access; they never grant
additional access.

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[PATCH 00/34] x86: Memory Protection Keys (v5) Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
  [PATCH 09/34] x86, pkeys: store protection in high VMA flags Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
    Re: [PATCH 09/34] x86, pkeys: store protection in high VMA flags Thomas Gleixner <tglx@linutronix.de> - 2015-12-08 15:20 +0100
  [PATCH 32/34] x86, pkeys: add pkey set/get syscalls Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
  [PATCH 29/34] x86: separate out LDT init from context init Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
  [PATCH 31/34] x86, pkeys: allocation/free syscalls Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
  [PATCH 12/34] signals, pkeys: notify userspace about protection key faults Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
  [PATCH 20/34] x86, pkeys: differentiate instruction fetches Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
    Re: [PATCH 20/34] x86, pkeys: differentiate instruction fetches Thomas Gleixner <tglx@linutronix.de> - 2015-12-08 19:20 +0100
  [PATCH 19/34] x86, pkeys: optimize fault handling in access_error() Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
    Re: [PATCH 19/34] x86, pkeys: optimize fault handling in  access_error() Thomas Gleixner <tglx@linutronix.de> - 2015-12-08 19:20 +0100
  [PATCH 18/34] mm: add gup flag to indicate "foreign" mm access Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
  [PATCH 27/34] x86, pkeys: make mprotect_key() mask off additional vm_flags Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
    Re: [PATCH 27/34] x86, pkeys: make mprotect_key() mask off additional  vm_flags Thomas Gleixner <tglx@linutronix.de> - 2015-12-08 19:50 +0100
  [PATCH 23/34] x86, pkeys: add Kconfig prompt to existing config option Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
    Re: [PATCH 23/34] x86, pkeys: add Kconfig prompt to existing config  option Thomas Gleixner <tglx@linutronix.de> - 2015-12-08 19:30 +0100
  [PATCH 25/34] x86, pkeys: add arch_validate_pkey() Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
    Re: [PATCH 25/34] x86, pkeys: add arch_validate_pkey() Thomas Gleixner <tglx@linutronix.de> - 2015-12-08 19:50 +0100
  [PATCH 33/34] x86, pkeys: actually enable Memory Protection Keys in CPU Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
  [PATCH 26/34] mm: implement new mprotect_key() system call Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
    Re: [PATCH 26/34] mm: implement new mprotect_key() system call "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2015-12-05 08:00 +0100
      Re: [PATCH 26/34] mm: implement new mprotect_key() system call Dave Hansen <dave@sr71.net> - 2015-12-07 17:50 +0100
        Re: [PATCH 26/34] mm: implement new mprotect_key() system call "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2015-12-09 12:10 +0100
          Re: [PATCH 26/34] mm: implement new mprotect_key() system call Dave Hansen <dave@sr71.net> - 2015-12-09 16:50 +0100
            Re: [PATCH 26/34] mm: implement new mprotect_key() system call "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2015-12-09 17:50 +0100
              Re: [PATCH 26/34] mm: implement new mprotect_key() system call Dave Hansen <dave@sr71.net> - 2015-12-09 18:10 +0100
                Re: [PATCH 26/34] mm: implement new mprotect_key() system call "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2015-12-11 21:20 +0100
  [PATCH 24/34] mm, multi-arch: pass a protection key in to calc_vm_flag_bits() Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
  [PATCH 22/34] x86, pkeys: dump PTE pkey in /proc/pid/smaps Dave Hansen <dave@sr71.net> - 2015-12-04 02:20 +0100
  [PATCH 14/34] x86, pkeys: add functions to fetch PKRU Dave Hansen <dave@sr71.net> - 2015-12-04 02:30 +0100
    Re: [PATCH 14/34] x86, pkeys: add functions to fetch PKRU Thomas Gleixner <tglx@linutronix.de> - 2015-12-08 16:20 +0100
  [PATCH 11/34] x86, pkeys: pass VMA down in to fault signal generation code Dave Hansen <dave@sr71.net> - 2015-12-04 02:30 +0100
  [PATCH 02/34] x86, fpu: add placeholder for Processor Trace XSAVE state Dave Hansen <dave@sr71.net> - 2015-12-04 02:30 +0100
  [PATCH 16/34] x86, mm: simplify get_user_pages() PTE bit handling Dave Hansen <dave@sr71.net> - 2015-12-04 02:30 +0100
    Re: [PATCH 16/34] x86, mm: simplify get_user_pages() PTE bit  handling Thomas Gleixner <tglx@linutronix.de> - 2015-12-08 19:10 +0100
      Re: [PATCH 16/34] x86, mm: simplify get_user_pages() PTE bit handling Dave Hansen <dave@sr71.net> - 2015-12-08 19:40 +0100
  [PATCH 10/34] x86, pkeys: arch-specific protection bits Dave Hansen <dave@sr71.net> - 2015-12-04 02:30 +0100
    Re: [PATCH 10/34] x86, pkeys: arch-specific protection bitsy Thomas Gleixner <tglx@linutronix.de> - 2015-12-08 16:20 +0100
      Re: [PATCH 10/34] x86, pkeys: arch-specific protection bitsy Dave Hansen <dave@sr71.net> - 2015-12-08 17:40 +0100
        Re: [PATCH 10/34] x86, pkeys: arch-specific protection bitsy Thomas Gleixner <tglx@linutronix.de> - 2015-12-08 18:30 +0100
          Re: [PATCH 10/34] x86, pkeys: arch-specific protection bitsy Dave Hansen <dave@sr71.net> - 2015-12-08 19:10 +0100
            Re: [PATCH 10/34] x86, pkeys: arch-specific protection bitsy Thomas Gleixner <tglx@linutronix.de> - 2015-12-08 19:40 +0100
            Re: [PATCH 10/34] x86, pkeys: arch-specific protection bitsy Thomas Gleixner <tglx@linutronix.de> - 2015-12-08 19:40 +0100
  [PATCH 06/34] x86, pkeys: add PKRU xsave fields and data structure(s) Dave Hansen <dave@sr71.net> - 2015-12-04 02:30 +0100
  [PATCH 05/34] x86, pkeys: define new CR4 bit Dave Hansen <dave@sr71.net> - 2015-12-04 02:30 +0100
  [PATCH 01/34] mm, gup: introduce concept of "foreign" get_user_pages() Dave Hansen <dave@sr71.net> - 2015-12-04 02:30 +0100
  [PATCH 17/34] x86, pkeys: check VMAs and PTEs for protection keys Dave Hansen <dave@sr71.net> - 2015-12-04 02:30 +0100
    Re: [PATCH 17/34] x86, pkeys: check VMAs and PTEs for protection  keys Thomas Gleixner <tglx@linutronix.de> - 2015-12-08 19:20 +0100
  [PATCH 13/34] x86, pkeys: fill in pkey field in siginfo Dave Hansen <dave@sr71.net> - 2015-12-04 02:30 +0100
  [PATCH 08/34] x86, pkeys: new page fault error code bit: PF_PK Dave Hansen <dave@sr71.net> - 2015-12-04 02:30 +0100
  [PATCH 07/34] x86, pkeys: PTE bits for storing protection key Dave Hansen <dave@sr71.net> - 2015-12-04 02:30 +0100
  [PATCH 04/34] x86, pkeys: cpuid bit definition Dave Hansen <dave@sr71.net> - 2015-12-04 02:30 +0100
  Re: [PATCH 00/34] x86: Memory Protection Keys (v5) Dave Hansen <dave@sr71.net> - 2015-12-05 00:40 +0100
    Re: [PATCH 00/34] x86: Memory Protection Keys (v5) Andy Lutomirski <luto@amacapital.net> - 2015-12-11 21:20 +0100
  Re: [PATCH 00/34] x86: Memory Protection Keys (v5) Andy Lutomirski <luto@amacapital.net> - 2015-12-05 00:40 +0100

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