linux-kernel - Re: [PATCH v2] powerpc: Default to enabling STRICT_KERNEL

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Date:   Fri, 6 Oct 2017 09:22:43 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Christophe LEROY <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] powerpc: Default to enabling STRICT_KERNEL_RWX

On Fri, Oct 6, 2017 at 6:03 AM, Kees Cook <keescook@...omium.org> wrote:
> When available, CONFIG_KERNEL_RWX should be default-enabled for PPC64.
> On PPC32, there is a performance trade-off.
>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Christophe LEROY <christophe.leroy@....fr>
> Cc: Balbir Singh <bsingharora@...il.com>
> Cc: linuxppc-dev@...ts.ozlabs.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> v2:
> - depend on PPC64, as noted by Christophe.
> ---
>  arch/powerpc/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 809c468edab1..4315c9b2db4f 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 if PPC64

We usually have CONFIG_RELOCATABLE on - on most configs. Our STRICT
RWX depends on !RELOCATABLE as you've seen. I have patches to fix
STRICT_KERNEL_RWX on CONFIG_RELOCATABLE

https://patchwork.ozlabs.org/patch/795744/ (I need to rebase this to
use generic helpers we have to convert an mm,addr to pte)
Aside, I also have set_memory_xx at
https://patchwork.ozlabs.org/patch/796183/ (again I need to rebase
them)

I hope to get to them next week, hopefully

Balbir Singh.