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Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap()

From "PaX Team" <pageexec@freemail.hu>
Newsgroups linux.kernel
Subject Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap()
Date 2017-04-10 12:50 +0200
Message-ID <tuF3s-7X5-7@gated-at.bofh.it> (permalink)
References <ttImK-3TM-5@gated-at.bofh.it> <tuF3s-7X5-9@gated-at.bofh.it> <tuvdL-1Fy-7@gated-at.bofh.it>
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On 9 Apr 2017 at 17:10, Andy Lutomirski wrote:

> On Sun, Apr 9, 2017 at 5:47 AM, PaX Team <pageexec@freemail.hu> wrote:
> > on x86 the cost of the pax_open/close_kernel primitives comes from the cr0
> > writes and nothing else, use_mm suffers not only from the cr3 writes but
> > also locking/atomic ops and cr4 writes on its path and the inevitable TLB
> > entry costs. and if cpu vendors cared enough, they could make toggling cr0.wp
> > a fast path in the microcode and reduce its overhead by an order of magnitude.
> >
> 
> If the CR4 writes happen in for this use case, that's a bug.

that depends on how you plan to handle perf/rdpmc users and how many
alternative mm structs you plan to manage (one global, one per cpu,
one per mm struct, etc).

> > you'll be duplicating TLB entries in the alternative PCID for both code
> > and data, where they will accumulate (=take room away from the normal PCID
> > and expose unwanted memory for access) unless you also flush them when
> > switching back (which then will cost even more cycles). also i'm not sure
> > that processors implement all the 12 PCID bits so depending on how many PCIDs
> > you plan to use, you could be causing even more unnecessary TLB replacements.
> >
> 
> Unless the CPU is rather dumber than I expect, the only duplicated
> entries should be for the writable aliases of pages that are written.
> The rest of the pages are global and should be shared for all PCIDs.

well, 4.10.2.4 has language like this (4.10.3.2 implies similar):

   A logical processor may use a global TLB entry to translate a linear
   address, even if the TLB entry is associated with a PCID different
   from the current PCID.

that to me says that global page entries are associated with a PCID and
may (not) be used while in another PCID. in Intel-speak that's not 'dumb'
but "tricks up our sleeve that we don't really want to tell you about in
detail, except perhaps under a NDA".

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[RFC v2] Introduce rare_write() infrastructure Kees Cook <keescook@chromium.org> - 2017-03-29 20:20 +0200
  [RFC v2][PATCH 10/11] gcc-plugins: Add constify plugin Kees Cook <keescook@chromium.org> - 2017-03-29 20:20 +0200
  [RFC v2][PATCH 03/11] net: switch sock_diag handlers to rare_write() Kees Cook <keescook@chromium.org> - 2017-03-29 20:20 +0200
  [RFC v2][PATCH 07/11] ARM: mm: set DOMAIN_WR_RARE for rodata Kees Cook <keescook@chromium.org> - 2017-03-29 20:20 +0200
  [RFC v2][PATCH 01/11] Introduce rare_write() infrastructure Kees Cook <keescook@chromium.org> - 2017-03-29 20:20 +0200
    Re: [RFC v2][PATCH 01/11] Introduce rare_write() infrastructure Kees Cook <keescook@chromium.org> - 2017-03-29 20:30 +0200
      Re: [RFC v2][PATCH 01/11] Introduce rare_write() infrastructure Ho-Eun Ryu <hoeun.ryu@gmail.com> - 2017-03-30 09:50 +0200
        Re: [RFC v2][PATCH 01/11] Introduce rare_write() infrastructure Kees Cook <keescook@chromium.org> - 2017-03-30 19:10 +0200
    Re: [RFC v2][PATCH 01/11] Introduce rare_write() infrastructure Ho-Eun Ryu <hoeun.ryu@gmail.com> - 2017-04-07 10:20 +0200
      Re: [RFC v2][PATCH 01/11] Introduce rare_write() infrastructure Kees Cook <keescook@chromium.org> - 2017-04-07 22:40 +0200
  [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Kees Cook <keescook@chromium.org> - 2017-03-29 20:20 +0200
    Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Andy Lutomirski <luto@amacapital.net> - 2017-03-30 00:40 +0200
      Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Kees Cook <keescook@chromium.org> - 2017-03-30 03:50 +0200
        Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Andy Lutomirski <luto@kernel.org> - 2017-04-06 02:00 +0200
          Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Kees Cook <keescook@chromium.org> - 2017-04-06 02:20 +0200
            Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Andy Lutomirski <luto@amacapital.net> - 2017-04-06 18:00 +0200
              Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Mathias Krause <minipli@googlemail.com> - 2017-04-07 10:40 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement  __arch_rare_write_begin/unmap() Thomas Gleixner <tglx@linutronix.de> - 2017-04-07 11:50 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Mathias Krause <minipli@googlemail.com> - 2017-04-07 13:00 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement  __arch_rare_write_begin/unmap() Thomas Gleixner <tglx@linutronix.de> - 2017-04-07 15:20 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Mathias Krause <minipli@googlemail.com> - 2017-04-07 15:40 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Andy Lutomirski <luto@kernel.org> - 2017-04-07 18:20 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement  __arch_rare_write_begin/unmap() Mark Rutland <mark.rutland@arm.com> - 2017-04-07 18:30 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() "PaX Team" <pageexec@freemail.hu> - 2017-04-07 22:10 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Andy Lutomirski <luto@kernel.org> - 2017-04-08 07:00 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() "PaX Team" <pageexec@freemail.hu> - 2017-04-09 14:50 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Andy Lutomirski <luto@kernel.org> - 2017-04-10 02:20 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() "PaX Team" <pageexec@freemail.hu> - 2017-04-10 12:50 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Andy Lutomirski <luto@kernel.org> - 2017-04-10 18:10 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement  __arch_rare_write_begin/unmap() Thomas Gleixner <tglx@linutronix.de> - 2017-04-07 22:50 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Kees Cook <keescook@chromium.org> - 2017-04-07 23:30 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Daniel Micay <danielmicay@gmail.com> - 2017-04-08 06:20 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Daniel Micay <danielmicay@gmail.com> - 2017-04-08 06:20 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Daniel Micay <danielmicay@gmail.com> - 2017-04-08 06:30 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Andy Lutomirski <luto@kernel.org> - 2017-04-08 07:10 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Daniel Micay <danielmicay@gmail.com> - 2017-04-08 09:40 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Andy Lutomirski <luto@kernel.org> - 2017-04-08 17:30 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement  __arch_rare_write_begin/unmap() Ingo Molnar <mingo@kernel.org> - 2017-04-09 13:00 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement  __arch_rare_write_begin/unmap() Mark Rutland <mark.rutland@arm.com> - 2017-04-10 12:30 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() "PaX Team" <pageexec@freemail.hu> - 2017-04-09 22:30 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Andy Lutomirski <luto@kernel.org> - 2017-04-10 02:40 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() "PaX Team" <pageexec@freemail.hu> - 2017-04-10 22:00 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Andy Lutomirski <luto@kernel.org> - 2017-04-10 22:30 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Kees Cook <keescook@chromium.org> - 2017-04-10 22:20 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() Andy Lutomirski <luto@kernel.org> - 2017-04-10 22:20 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement  __arch_rare_write_begin/unmap() Thomas Gleixner <tglx@linutronix.de> - 2017-04-07 21:30 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement  __arch_rare_write_begin/unmap() Peter Zijlstra <peterz@infradead.org> - 2017-04-07 16:50 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement  __arch_rare_write_begin/unmap() Mark Rutland <mark.rutland@arm.com> - 2017-04-10 12:40 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() "PaX Team" <pageexec@freemail.hu> - 2017-04-07 22:40 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement  __arch_rare_write_begin/unmap() Thomas Gleixner <tglx@linutronix.de> - 2017-04-10 10:30 +0200
                Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() "PaX Team" <pageexec@freemail.hu> - 2017-04-10 22:00 +0200
    Re: [RFC v2][PATCH 04/11] x86: Implement  __arch_rare_write_begin/unmap() Peter Zijlstra <peterz@infradead.org> - 2017-04-07 11:40 +0200
  [RFC v2][PATCH 09/11] list: add rare_write() list helpers Kees Cook <keescook@chromium.org> - 2017-03-29 20:20 +0200
  [RFC v2][PATCH 05/11] ARM: mm: dump: Add domain to output Kees Cook <keescook@chromium.org> - 2017-03-29 20:20 +0200
  [RFC v2][PATCH 11/11] cgroups: force all struct cftype const Kees Cook <keescook@chromium.org> - 2017-03-29 20:20 +0200
  [RFC v2][PATCH 08/11] ARM: Implement __arch_rare_write_begin/end() Kees Cook <keescook@chromium.org> - 2017-03-29 20:20 +0200
    Re: [RFC v2][PATCH 08/11] ARM: Implement  __arch_rare_write_begin/end() Peter Zijlstra <peterz@infradead.org> - 2017-04-07 11:40 +0200
  [RFC v2][PATCH 02/11] lkdtm: add test for rare_write() infrastructure Kees Cook <keescook@chromium.org> - 2017-03-29 20:20 +0200
    Re: [kernel-hardening] [RFC v2][PATCH 02/11] lkdtm: add test for  rare_write() infrastructure Ian Campbell <ijc@hellion.org.uk> - 2017-03-30 12:20 +0200
      Re: [kernel-hardening] [RFC v2][PATCH 02/11] lkdtm: add test for  rare_write() infrastructure Kees Cook <keescook@chromium.org> - 2017-03-30 18:20 +0200
  Re: [RFC v2] Introduce rare_write() infrastructure Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-03-29 21:10 +0200
    Re: [RFC v2] Introduce rare_write() infrastructure Kees Cook <keescook@chromium.org> - 2017-03-29 21:20 +0200

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