[PATCH v14 3/9] powerpc/modules: Make module_alloc() Strict Module RWX aware

[Christophe Leroy]

Le 17/05/2021 à 13:01, Michael Ellerman a écrit :
> Jordan Niethe <jniethe5 at gmail.com> writes:
>> On Mon, May 17, 2021 at 4:37 PM Christophe Leroy
>> <christophe.leroy at csgroup.eu> wrote:
>>> Le 17/05/2021 à 05:28, Jordan Niethe a écrit :
>>>> Make module_alloc() use PAGE_KERNEL protections instead of
>>>> PAGE_KERNEL_EXEX if Strict Module RWX is enabled.
>>>>
>>>> Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
>>>> ---
>>>> v14: - Split out from powerpc: Set ARCH_HAS_STRICT_MODULE_RWX
>>>>        - Add and use strict_module_rwx_enabled() helper
>>>> ---
>>>>    arch/powerpc/include/asm/mmu.h | 5 +++++
>>>>    arch/powerpc/kernel/module.c   | 4 +++-
>>>>    2 files changed, 8 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
>>>> index 607168b1aef4..7710bf0cbf8a 100644
>>>> --- a/arch/powerpc/include/asm/mmu.h
>>>> +++ b/arch/powerpc/include/asm/mmu.h
>>>> @@ -357,6 +357,11 @@ static inline bool strict_kernel_rwx_enabled(void)
>>>>        return false;
>>>>    }
>>>>    #endif
>>>> +
>>>> +static inline bool strict_module_rwx_enabled(void)
>>>> +{
>>>> +     return IS_ENABLED(CONFIG_STRICT_MODULE_RWX) && strict_kernel_rwx_enabled();
>>>> +}
>>>
>>> Looking at arch/Kconfig, I have the feeling that it is possible to select CONFIG_STRICT_MODULE_RWX
>>> without selecting CONFIG_STRICT_KERNEL_RWX.
>>>
>>> In that case, strict_kernel_rwx_enabled() will return false.
> 
>> Ok, if someone did that currently it would break things, e.g. code
>> patching. I think it should it be made impossible to
>> CONFIG_STRICT_MODULE_RWX without CONFIG_STRICT_KERNEL_RWX?
> 
> Yeah I don't see any reason to support that combination.
> 
> We should be moving to a world where both are on by default, or in fact
> are always enabled.
> 

Would it work if we add the following in arch/powerpc/Kconfig ? :

	select STRICT_KERNEL_RWX if STRICT_MODULE_RWX

There should be no dependency issue as powerpc only selects ARCH_HAS_STRICT_MODULE_RWX when 
ARCH_HAS_STRICT_KERNEL_RWX is also selected.

Christophe