Re: [PATCH v2 5/5] powerpc: Select ARCH_WANTS_MODULES_DATA_IN_VMALLOC on book3s/32 and 8xx

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 03/02/2022 à 06:39, Michael Ellerman a écrit :
> 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.
> 

Was an easy way to copy you automatically with 'git send-email', but 
getting it through linuxppc-dev list is enough I guess ?

Christophe