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Date: Mon, 2 Jul 2018 13:54:36 -0700
From: Kees Cook <>
To: Chris von Recklinghausen <>
Cc: Laura Abbott <>, Paolo Abeni <>, 
	LKML <>, Linux-MM <>, 
	Kernel Hardening <>, Josh Poimboeuf <>, 
	Peter Zijlstra <>
Subject: Re: [PATCH v3] add param that allows bootline control of hardened usercopy

On Mon, Jul 2, 2018 at 11:55 AM, Christoph von Recklinghausen
<> wrote:
> On 07/02/2018 02:43 PM, Kees Cook wrote:
>> On Sat, Jun 30, 2018 at 1:43 PM, Christoph von Recklinghausen
>> <> wrote:
>>> The last issue I'm chasing is build failures on ARCH=m68k. The error is
>>> atomic_read and friends needed by the jump label code not being found.
>>> The config has CONFIG_BROKEN_ON_SMP=y, so the jump label calls I added
>>> will only be made #ifndef CONFIG_BROKEN_ON_SMP. Do you think that's
>>> worth a mention in the blurb that's added to
>>> Documentation/admin-guide/kernel-parameters.txt?
>> Uhm, that's weird -- I think the configs on m68k need fixing then? I
>> don't want to have to sprinkle that ifdef in generic code.
>> How are other users of static keys and jump labels dealing with m68k weirdness?
> There's also CONFIG_JUMP_LABEL which is defined in x86_64 but not
> defined in the m68k configs. I'll use that instead. In hindsight I
> should have spotted that but didn't.

I think what I mean is that jump labels should always work. There
shouldn't be a need to #ifdef the common usercopy code. i.e.
include/linux/jump_label.h should work on all architectures already. I
see HAVE_JUMP_LABEL tests there, for example:

#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)

Other core code uses static keys without this; what is the failing combination?


Kees Cook
Pixel Security

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