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Subject: Re: [PATCH v14 7/9] powerpc: Set ARCH_HAS_STRICT_MODULE_RWX
To: Jordan Niethe <jniethe5@gmail.com>, linuxppc-dev@lists.ozlabs.org
References: <20210517032810.129949-1-jniethe5@gmail.com>
 <20210517032810.129949-8-jniethe5@gmail.com>
From: Christophe Leroy <christophe.leroy@csgroup.eu>
Message-ID: <5c592104-2018-a36d-61a3-e2039b1563eb@csgroup.eu>
Date: Mon, 17 May 2021 08:48:11 +0200
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Le 17/05/2021 à 05:28, Jordan Niethe a écrit :
> From: Russell Currey <ruscur@russell.cc>
> 
> To enable strict module RWX on powerpc, set:
> 
>      CONFIG_STRICT_MODULE_RWX=y
> 
> You should also have CONFIG_STRICT_KERNEL_RWX=y set to have any real
> security benefit.
> 
> ARCH_HAS_STRICT_MODULE_RWX is set to require ARCH_HAS_STRICT_KERNEL_RWX.
> This is due to a quirk in arch/Kconfig and arch/powerpc/Kconfig that
> makes STRICT_MODULE_RWX *on by default* in configurations where
> STRICT_KERNEL_RWX is *unavailable*.
> 
> Since this doesn't make much sense, and module RWX without kernel RWX
> doesn't make much sense, having the same dependencies as kernel RWX
> works around this problem.
> 
> Book32s/32 processors with a hash mmu (i.e. 604 core) can not set memory
   ^^^^^^

Book32s ==> Book3s

> protection on a page by page basis so do not enable.

It is not exactly that. The problem on 604 is for _exec_ protection.

Note that on book3s/32, on both 603 and 604 core, it is not possible to write protect kernel pages. 
So maybe it would make sense to disable ARCH_HAS_STRICT_MODULE_RWX on CONFIG_PPC_BOOK3S_32 
completely, I'm not sure.


> 
> Signed-off-by: Russell Currey <ruscur@russell.cc>
> [jpn: - predicate on !PPC_BOOK3S_604
>        - make module_alloc() use PAGE_KERNEL protection]
> Signed-off-by: Jordan Niethe <jniethe5@gmail.com>

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>

> ---
> v10: - Predicate on !PPC_BOOK3S_604
>       - Make module_alloc() use PAGE_KERNEL protection
> v11: - Neaten up
> v13: Use strict_kernel_rwx_enabled()
> v14: Make changes to module_alloc() its own commit
> ---
>   arch/powerpc/Kconfig | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index cce0a137b046..cb5d9d862c35 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -140,6 +140,7 @@ config PPC
>   	select ARCH_HAS_SCALED_CPUTIME		if VIRT_CPU_ACCOUNTING_NATIVE && PPC_BOOK3S_64
>   	select ARCH_HAS_SET_MEMORY
>   	select ARCH_HAS_STRICT_KERNEL_RWX	if ((PPC_BOOK3S_64 || PPC32) && !HIBERNATION)
> +	select ARCH_HAS_STRICT_MODULE_RWX	if ARCH_HAS_STRICT_KERNEL_RWX && !PPC_BOOK3S_604
>   	select ARCH_HAS_TICK_BROADCAST		if GENERIC_CLOCKEVENTS_BROADCAST
>   	select ARCH_HAS_UACCESS_FLUSHCACHE
>   	select ARCH_HAS_COPY_MC			if PPC64
>