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

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Message-ID: <9cab4adb-bd4b-48d5-d63c-33a0f25c97e4@csgroup.eu>
Date:   Thu, 3 Feb 2022 07:07:23 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>
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



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 ?

Christophe