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Reply-To: crecklin@redhat.com
Subject: Re: [PATCH v3] add param that allows bootline control of hardened
 usercopy
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From: Christoph von Recklinghausen <crecklin@redhat.com>
Message-ID: <5f21bb3c-0165-38d1-b68b-96d53c2b70f4@redhat.com>
Date: Mon, 2 Jul 2018 18:23:44 -0400
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To: Kees Cook <keescook@chromium.org>
Cc: Laura Abbott <labbott@redhat.com>, Paolo Abeni <pabeni@redhat.com>, LKML <linux-kernel@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>, Kernel Hardening <kernel-hardening@lists.openwall.com>, Josh Poimboeuf <jpoimboe@redhat.com>, Peter Zijlstra <peterz@infradead.org>

On 07/02/2018 04:54 PM, Kees Cook wrote:
> On Mon, Jul 2, 2018 at 11:55 AM, Christoph von Recklinghausen
> <crecklin@redhat.com> wrote:
>> On 07/02/2018 02:43 PM, Kees Cook wrote:
>>> On Sat, Jun 30, 2018 at 1:43 PM, Christoph von Recklinghausen
>>> <crecklin@redhat.com> 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)
> # define HAVE_JUMP_LABEL
> #endif
>
> Other core code uses static keys without this; what is the failing combination?

The complaints were when there was jump_label code in
include/linux/thread_info.h. Now that the code is isolated to
mm/usercopy.c, it successfully builds for m68k with mention of
CONFIG_JUMP_LABEL and CONFIG_SMP_BROKEN removed.

I'll send out a new patch in the morning after I test some more.

Thanks,

Chris


> -Kees
>