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Groups > linux.kernel > #1619575
| From | Andy Lutomirski <luto@kernel.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement __arch_rare_write_begin/unmap() |
| Date | 2017-04-10 02:20 +0200 |
| Message-ID | <tuvdL-1Fy-7@gated-at.bofh.it> (permalink) |
| References | <tqqml-2iB-7@gated-at.bofh.it> <ttImK-3TM-3@gated-at.bofh.it> <ttQDE-FB-11@gated-at.bofh.it> <tuks1-2PA-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Sun, Apr 9, 2017 at 5:47 AM, PaX Team <pageexec@freemail.hu> wrote: > On 7 Apr 2017 at 21:58, Andy Lutomirski wrote: > >> On Fri, Apr 7, 2017 at 12:58 PM, PaX Team <pageexec@freemail.hu> wrote: >> > On 7 Apr 2017 at 9:14, Andy Lutomirski wrote: >> >> Then someone who cares about performance can benchmark the CR0.WP >> >> approach against it and try to argue that it's a good idea. This >> >> benchmark should wait until I'm done with my PCID work, because PCID >> >> is going to make use_mm() a whole heck of a lot faster. >> > >> > in my measurements switching PCID is hovers around 230 cycles for snb-ivb >> > and 200-220 for hsw-skl whereas cr0 writes are around 230-240 cycles. there's >> > of course a whole lot more impact for switching address spaces so it'll never >> > be fast enough to beat cr0.wp. >> > >> >> If I'm reading this right, you're saying that a non-flushing CR3 write >> is about the same cost as a CR0.WP write. If so, then why should CR0 >> be preferred over the (arch-neutral) CR3 approach? > > cr3 (page table switching) isn't arch neutral at all ;). you probably meant > the higher level primitives except they're not enough to implement the scheme > as discussed before since the enter/exit paths are very much arch dependent. Yes. > > 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. >> And why would switching address spaces obviously be much slower? >> There'll be a very small number of TLB fills needed for the actual >> protected access. > > 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. --Andy
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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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