linux-kernel - Re: [PATCH v2 5/5] powerpc: Select ARCH_WANTS_MODULES_DATA_IN

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Message-ID: <877da7mq2d.fsf@mpe.ellerman.id.au>
Date:   Mon, 07 Feb 2022 12:19:06 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Jessica Yu <jeyu@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "kgdb-bugreport@...ts.sourceforge.net" 
        <kgdb-bugreport@...ts.sourceforge.net>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH v2 5/5] powerpc: Select
 ARCH_WANTS_MODULES_DATA_IN_VMALLOC on book3s/32 and 8xx

Christophe Leroy <christophe.leroy@...roup.eu> writes:
> Le 03/02/2022 à 06:39, Michael Ellerman a écrit :
>> Luis Chamberlain <mcgrof@...nel.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@...roup.eu>
>>>> Cc: Michael Ellerman <mpe@...erman.id.au>
>>>> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
>>>> Cc: Paul Mackerras <paulus@...ba.org>
>>>
>>> Cc list first and then the SOB.
>> 
>> Just delete the Cc: list, it's meaningless.
>> 
>
> Was an easy way to copy you automatically with 'git send-email', but 
> getting it through linuxppc-dev list is enough I guess ?

It's useful for making the tooling Cc the right people, it's fine to use
them for that.

But there's no value in committing them to the git history, I actively
strip them when applying. The fact that someone is Cc'ed on a patch
tells you nothing, given the volume of mail maintainers receive.

The link tag back to the original submission gives you the Cc list
anyway.

cheers