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Groups > linux.kernel > #1613262
| From | Kees Cook <keescook@chromium.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [kernel-hardening] [RFC v2][PATCH 02/11] lkdtm: add test for rare_write() infrastructure |
| Date | 2017-03-30 18:20 +0200 |
| Message-ID | <tqKXN-ry-25@gated-at.bofh.it> (permalink) |
| References | <tqqml-2iB-7@gated-at.bofh.it> <tqqmn-2iB-51@gated-at.bofh.it> <tqFlo-4ME-29@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Thu, Mar 30, 2017 at 2:34 AM, Ian Campbell <ijc@hellion.org.uk> wrote:
> On Wed, 2017-03-29 at 11:15 -0700, Kees Cook wrote:
>> diff --git a/drivers/misc/lkdtm_perms.c b/drivers/misc/lkdtm_perms.c
>> index c7635a79341f..8fbadfa4cc34 100644
>> --- a/drivers/misc/lkdtm_perms.c
>> +++ b/drivers/misc/lkdtm_perms.c
>> [...]
>> +/* This is marked __wr_rare, so it should ultimately be .rodata. */
>> +static unsigned long wr_rare __wr_rare = 0xAA66AA66;
>> [...]
>> +void lkdtm_WRITE_RARE_WRITE(void)
>> +{
>> + /* Explicitly cast away "const" for the test. */
>
> wr_rare isn't actually declared const above though? I don't think
> __wr_rare includes a const, apologies if I missed it.
Yeah, good point. I think this was a left-over from an earlier version
where I'd forgotten about that detail.
> OOI, if wr_rare _were_ const then can the compiler optimise the a pair
> of reads spanning the rare_write? i.e. adding const to the declaration
> above to get:
>
> static const unsigned long wr_rare __wr_rare = 0xAA66AA66;
> x = wr_read;
> rare_write(x, 0xf000baaa);
> y = wr_read;
>
> Is it possible that x == y == 0xaa66aa66 because gcc realises the x and
> y came from the same const location? Have I missed a clobber somewhere
> (I can't actually find a definition of __arch_rare_write_memcpy in this
> series so maybe it's there), or is such code expected to always cast
> away the const first?
>
> I suppose such constructs are rare in practice in the sorts of places
> where rare_write is appropriate, but with aggressive inlining it could
> occur as an unexpected trap for the unwary perhaps.
Right, __wr_rare is actually marked as .data..ro_after_init, which gcc
effectively ignores (thinking it's part of .data), but the linker
script later movies this section into the read-only portion with
.rodata. As a result, the compiler treats it as writable, but the
storage location is actually read-only.
(And, AIUI, the constify plugin makes things read-only in a similar
way, though I think it's more subtle but still avoids the
const-optimization dangers.)
-Kees
--
Kees Cook
Pixel Security
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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() 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() 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: [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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