From: Arnd Bergmann <arnd@arndb.de>
To: Kees Cook <keescook@chromium.org>
Cc: Kernel Hardening <kernel-hardening@lists.openwall.com>,
Laura Abbott <labbott@redhat.com>,
"the arch/x86 maintainers" <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Russell King - ARM Linux <linux@armlinux.org.uk>,
Nicolas Pitre <nicolas.pitre@linaro.org>,
Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH v2 04/20] gcc-plugins: Add the randstruct plugin
Date: Fri, 30 Jun 2017 09:35:12 +0200 [thread overview]
Message-ID: <CAK8P3a0HeP0ekoZCu9+d-4y0dUz2=-Nn53=fTHPKSJao2NMU5Q@mail.gmail.com> (raw)
In-Reply-To: <CAGXu5jJHRC83YSDKVfm4_41k0wgqfG=wpqPQss-ce77SRNkwRA@mail.gmail.com>
On Fri, Jun 30, 2017 at 12:53 AM, Kees Cook <keescook@chromium.org> wrote:
> On Thu, Jun 29, 2017 at 3:08 PM, Arnd Bergmann <arnd@arndb.de> wrote:
>> On Fri, May 26, 2017 at 10:17 PM, Kees Cook <keescook@chromium.org> wrote:
>> I noticed new build errors that bisected back to this patch, which has
>> now showed up
>> in linux-next again:
>
> (FWIW this is randstruct not initify, and has been in -next for a
> couple weeks now.)
I first saw it last week and only now got around to looking any deeper,
as I had assumed that one of my own patches caused it.
>> /git/arm-soc/arch/arm/kernel/entry-armv.S: Assembler messages:
>> /git/arm-soc/arch/arm/kernel/entry-armv.S:800: Error: bad immediate
>> value for offset (4644)
>> /git/arm-soc/scripts/Makefile.build:403: recipe for target
>> 'arch/arm/kernel/entry-armv.o' failed
>> make[3]: *** [arch/arm/kernel/entry-armv.o] Error 1
>> /git/arm-soc/arch/arm/kernel/entry-armv.S: Assembler messages:
>> /git/arm-soc/arch/arm/kernel/entry-armv.S:800: Error: bad immediate
>> value for offset (5584)
>
> arch/arm/kernel/entry-armv.S: ldr r7, [r7, #TSK_STACK_CANARY]
> arch/arm/kernel/asm-offsets.c: DEFINE(TSK_STACK_CANARY,
> offsetof(struct task_struct, stack_canary));
>
> This would imply that stack_canary got randomized to an offset within
> struct task_struct beyond the "ldr" immediate range (4096). Yay for
> giant structs.
>
> I'm surprised this didn't bisect to "task_struct: Allow randomized layout".
The bisection was a bit tricky, it's very possible that this should have
been the one to report.
>> /git/arm-soc/scripts/Makefile.build:403: recipe for target
>> 'arch/arm/kernel/entry-armv.o' failed
>> make[3]: *** [arch/arm/kernel/entry-armv.o] Error 1
>> /git/arm-soc/arch/arm/mm/tlb-v4.S: Assembler messages:
>> /git/arm-soc/arch/arm/mm/tlb-v4.S:35: Error: bad immediate value for
>> offset (4928)
>
> Similar:
>
> act_mm r3 @ get current->active_mm
> ...
> .macro act_mm, rd
> ldr \rd, [\rd, #TSK_ACTIVE_MM]
> ...
> kernel/asm-offsets.c: DEFINE(TSK_ACTIVE_MM,
> offsetof(struct task_struct, active_mm));
>
>> /git/arm-soc/scripts/Makefile.build:403: recipe for target
>> 'arch/arm/mm/tlb-v4.o' failed
>> make[3]: *** [arch/arm/mm/tlb-v4.o] Error 1
>> /git/arm-soc/arch/arm/mm/tlb-v4wbi.S: Assembler messages:
>> /git/arm-soc/arch/arm/mm/tlb-v4wbi.S:34: Error: bad immediate value
>> for offset (4928)
>> /git/arm-soc/scripts/Makefile.build:403: recipe for target
>> 'arch/arm/mm/tlb-v4wbi.o' failed
>
> Same as above.
>
>> So far, that's the only thing that goes wrong for me though, and this
>> is probably
>> easy to fix.
>
> Thanks for letting me know! These haven't shown up in my tests since I
> haven't gotten "unlucky" in randomizing the task_struct, it seems.
I've only hit it a couple of times a few thousand builds.
> I see a few possible solutions:
>
> - ignore it and try your build again with a fresh tree and a new
> randomization seed ;)
> - remove "depends on !COMPILE_TEST" from
> GCC_PLUGIN_RANDSTRUCT_PERFORMANCE, which will leave most stuff near
> their original locations
> - add a new annotation __randomize_cacheline which performs the same
> logic as above, but only for the marked structure
> - build new logic to keep certain fields (with some special marking)
> within a given range of their original position
> - rewrite the ARM code to handle larger immediates
>
> The first obviously won't fly. The second just bypasses the problem
> forcing it to be exposed by other people later. The third is likely
> easiest to do now, but reduces the effectiveness of randomization for
> architectures that don't have sensitive immediate values. The fourth
> sounds not generally useful. The fifth may be unacceptable to arm
> maintainers due to performance impacts.
I was thinking of the fifth solution, but don't know exactly how to
do it. If performance is a concern, I guess we could have separate
implementations for randstruct and traditional builds.
I've added a few more people to Cc that may know exactly how to
do it right.
> Can you verify that reverting "task_struct: Allow randomized layout"
> fixes a bugged build for you?
Confirmed.
Arnd
next prev parent reply other threads:[~2017-06-30 7:35 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-26 20:17 [PATCH v2 00/20] Introduce struct layout randomization plugin Kees Cook
2017-05-26 20:17 ` [PATCH v2 01/20] NFS: Avoid cross-structure casting Kees Cook
2017-05-28 7:53 ` Christoph Hellwig
2017-05-28 16:55 ` Kees Cook
2017-05-26 20:17 ` [PATCH v2 02/20] gcc-plugins: Detail c-common.h location for GCC 4.6 Kees Cook
2017-05-26 20:17 ` [PATCH v2 03/20] compiler: Add __designated_init annotation Kees Cook
2017-05-26 20:17 ` [PATCH v2 04/20] gcc-plugins: Add the randstruct plugin Kees Cook
2017-06-29 22:08 ` Arnd Bergmann
2017-06-29 22:53 ` Kees Cook
2017-06-30 0:04 ` Kees Cook
2017-06-30 7:35 ` Arnd Bergmann [this message]
2017-06-30 7:55 ` Ard Biesheuvel
2017-06-30 8:27 ` Arnd Bergmann
2017-06-30 14:41 ` Kees Cook
2017-06-30 15:22 ` Arnd Bergmann
2017-05-26 20:17 ` [PATCH v2 05/20] randstruct: Whitelist struct security_hook_heads cast Kees Cook
2017-05-27 8:41 ` Christoph Hellwig
2017-05-27 20:09 ` Kees Cook
2017-05-27 22:04 ` Tetsuo Handa
2017-05-28 0:43 ` [kernel-hardening] " Kees Cook
2017-05-30 10:34 ` James Morris
2017-05-26 20:17 ` [PATCH v2 06/20] randstruct: Whitelist UNIXCB cast Kees Cook
2017-05-26 20:20 ` Kees Cook
2017-05-28 7:56 ` Christoph Hellwig
2017-05-26 20:17 ` [PATCH v2 07/20] randstruct: Whitelist big_key path struct overloading Kees Cook
2017-05-28 8:12 ` Christoph Hellwig
2017-05-28 16:59 ` Kees Cook
2017-06-19 19:24 ` Kees Cook
2017-09-07 7:20 ` Christoph Hellwig
2017-09-07 22:55 ` Kees Cook
2017-05-26 20:17 ` [PATCH v2 08/20] randstruct: Whitelist NIU struct page overloading Kees Cook
2017-05-28 8:15 ` Christoph Hellwig
2017-05-28 17:35 ` Kees Cook
2017-05-28 17:37 ` Kees Cook
2017-05-26 20:17 ` [PATCH v2 09/20] randstruct: Mark various structs for randomization Kees Cook
2017-05-26 20:17 ` [PATCH v2 10/20] randstruct: opt-out externally exposed function pointer structs Kees Cook
2017-05-26 20:17 ` [PATCH v2 11/20] randstruct: Disable randomization of ACPICA structs Kees Cook
2017-05-27 8:42 ` Christoph Hellwig
2017-05-27 20:03 ` Kees Cook
2017-05-28 4:55 ` Christoph Hellwig
2017-05-26 20:17 ` [PATCH v2 12/20] sgi-xp: Use designated initializers Kees Cook
2017-05-27 8:44 ` Christoph Hellwig
2017-05-26 20:17 ` [PATCH v2 13/20] drm/amdgpu: " Kees Cook
2017-05-26 20:17 ` [PATCH v2 14/20] drm/amd/powerplay: " Kees Cook
2017-05-27 8:47 ` Christoph Hellwig
2017-05-27 20:10 ` Kees Cook
2017-05-26 20:17 ` [PATCH v2 15/20] mtk-vcodec: " Kees Cook
2017-05-26 20:17 ` [PATCH v2 16/20] ntfs: Use ERR_CAST() to avoid cross-structure cast Kees Cook
2017-05-26 20:17 ` [PATCH v2 17/20] ocfs2: " Kees Cook
2017-05-26 20:17 ` [PATCH v2 18/20] randstruct: Enable function pointer struct detection Kees Cook
2017-05-26 20:17 ` [PATCH v2 19/20] [RFC] task_struct: Allow randomized layout Kees Cook
2017-05-26 20:23 ` Linus Torvalds
2017-05-26 20:32 ` Kees Cook
2017-05-26 20:17 ` [PATCH v2 20/20] ACPICA: Use designated initializers Kees Cook
2017-05-28 7:45 ` Christoph Hellwig
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