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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Luis Chamberlain <mcgrof@kernel.org>,
        Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     Jessica Yu <jeyu@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
        "kgdb-bugreport@lists.sourceforge.net" 
        <kgdb-bugreport@lists.sourceforge.net>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>
Subject: Re: [PATCH v2 5/5] powerpc: Select
 ARCH_WANTS_MODULES_DATA_IN_VMALLOC on book3s/32 and 8xx
In-Reply-To: <YfsVhcpVTW0+YCl5@bombadil.infradead.org>
References: <cover.1643282353.git.christophe.leroy@csgroup.eu>
 <a20285472ad0a0a13a1d93c4707180be5b4fa092.1643282353.git.christophe.leroy@csgroup.eu>
 <YfsVhcpVTW0+YCl5@bombadil.infradead.org>
Date:   Thu, 03 Feb 2022 16:39:02 +1100
Message-ID: <87h79gmrux.fsf@mpe.ellerman.id.au>
MIME-Version: 1.0
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Precedence: bulk

Luis Chamberlain <mcgrof@kernel.org> writes:
> On Thu, Jan 27, 2022 at 11:28:12AM +0000, Christophe Leroy wrote:
>> book3s/32 and 8xx have a separate area for allocating modules,
>> defined by MODULES_VADDR / MODULES_END.
>> 
>> On book3s/32, it is not possible to protect against execution
>> on a page basis. A full 256M segment is either Exec or NoExec.
>> The module area is in an Exec segment while vmalloc area is
>> in a NoExec segment.
>> 
>> In order to protect module data against execution, select
>> ARCH_WANTS_MODULES_DATA_IN_VMALLOC.
>> 
>> For the 8xx (and possibly other 32 bits platform in the future),
>> there is no such constraint on Exec/NoExec protection, however
>> there is a critical distance between kernel functions and callers
>> that needs to remain below 32Mbytes in order to avoid costly
>> trampolines. By allocating data outside of module area, we
>> increase the chance for module text to remain within acceptable
>> distance from kernel core text.
>> 
>> So select ARCH_WANTS_MODULES_DATA_IN_VMALLOC for 8xx as well.
>> 
>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>> Cc: Paul Mackerras <paulus@samba.org>
>
> Cc list first and then the SOB.

Just delete the Cc: list, it's meaningless.

cheers