linux-kernel - Re: [PATCH] powerpc: Default to enabling STRICT_KERNEL

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Date:   Thu, 5 Oct 2017 10:30:25 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christophe LEROY <christophe.leroy@....fr>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Paul Mackerras <paulus@...ba.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] powerpc: Default to enabling STRICT_KERNEL_RWX

On Thu, Oct 5, 2017 at 12:49 AM, Christophe LEROY
<christophe.leroy@....fr> wrote:
>
>
> Le 05/10/2017 à 05:45, Kees Cook a écrit :
>>
>> When available, CONFIG_KERNEL_RWX should be default-enabled.
>
>
> On PPC32, this option implies deactivating BATs and/or LTLB mapping of the
> linear kernel address space, hence a significant performance degradation.
>
> So at least on PPC32, it should remain unselected by default.

Alright, sounds fine to me. Would this be okay?

+       select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if !PPC64

-Kees

>
> Christophe
>
>
>>
>> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
>> Cc: Paul Mackerras <paulus@...ba.org>
>> Cc: Michael Ellerman <mpe@...erman.id.au>
>> Cc: linuxppc-dev@...ts.ozlabs.org
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>>   arch/powerpc/Kconfig | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index 809c468edab1..9a549bbfc278 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -178,6 +178,7 @@ config PPC
>>         select HAVE_ARCH_TRACEHOOK
>>         select ARCH_HAS_STRICT_KERNEL_RWX       if ((PPC_BOOK3S_64 ||
>> PPC32) && !RELOCATABLE && !HIBERNATION)
>>         select ARCH_OPTIONAL_KERNEL_RWX         if
>> ARCH_HAS_STRICT_KERNEL_RWX
>> +       select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
>>         select HAVE_CBPF_JIT                    if !PPC64
>>         select HAVE_CONTEXT_TRACKING            if PPC64
>>         select HAVE_DEBUG_KMEMLEAK
>>
>



-- 
Kees Cook
Pixel Security