Re: [PATCH v11 3/9] powerpc: Always define MODULES_{VADDR,END}

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

Le 03/05/2021 à 08:16, Jordan Niethe a écrit :
> On Mon, May 3, 2021 at 3:57 PM Christophe Leroy
> <christophe.leroy@csgroup.eu> wrote:
>>
>>
>>
>> Le 03/05/2021 à 07:39, Jordan Niethe a écrit :
>>> On Thu, Apr 29, 2021 at 3:04 PM Christophe Leroy
>>> <christophe.leroy@csgroup.eu> wrote:
>>>>
>>>>
>>>>
>>>> Le 29/04/2021 à 05:15, Jordan Niethe a écrit :
>>>>> If MODULES_{VADDR,END} are not defined set them to VMALLOC_START and
>>>>> VMALLOC_END respectively. This reduces the need for special cases. For
>>>>> example, powerpc's module_alloc() was previously predicated on
>>>>> MODULES_VADDR being defined but now is unconditionally defined.
>>>>>
>>>>> This will be useful reducing conditional code in other places that need
>>>>> to allocate from the module region (i.e., kprobes).
>>>>>
>>>>> Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
>>>>> ---
>>>>> v10: New to series
>>>>> v11: - Consider more places MODULES_VADDR was being used
>>>>> ---
>>>>>     arch/powerpc/include/asm/pgtable.h    | 11 +++++++++++
>>>>>     arch/powerpc/kernel/module.c          |  5 +----
>>>>>     arch/powerpc/mm/kasan/kasan_init_32.c | 10 +++++-----
>>>>>     arch/powerpc/mm/ptdump/ptdump.c       |  4 ++--
>>>>>     4 files changed, 19 insertions(+), 11 deletions(-)
>>>>>
>>>>> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
>>>>> index c6a676714f04..882fda779648 100644
>>>>> --- a/arch/powerpc/include/asm/pgtable.h
>>>>> +++ b/arch/powerpc/include/asm/pgtable.h
>>>>> @@ -39,6 +39,17 @@ struct mm_struct;
>>>>>     #define __S110      PAGE_SHARED_X
>>>>>     #define __S111      PAGE_SHARED_X
>>>>>
>>>>> +#ifndef MODULES_VADDR
>>>>> +#define MODULES_VADDR VMALLOC_START
>>>>> +#define MODULES_END VMALLOC_END
>>>>> +#endif
>>>>> +
>>>>> +#if defined(CONFIG_PPC_BOOK3S_32) && defined(CONFIG_STRICT_KERNEL_RWX)
>>>>
>>>> No no.
>>>>
>>>> TASK_SIZE > MODULES_VADDR is ALWAYS wrong, for any target, in any configuration.
>>>>
>>>> Why is it a problem to leave the test as a BUILD_BUG_ON() in module_alloc() ?
>>> On ppc64s, MODULES_VADDR is __vmalloc_start (a variable)  and
>>> TASK_SIZE depends on current.
>>> Also for nohash like 44x, MODULES_VADDR is defined based on high_memory.
>>> If I put it back in module_alloc() and wrap it with #ifdef
>>> CONFIG_PPC_BOOK3S_32 will that be fine?
>>
>> Thinking about it once more, I think the best approach is the one taken by Nick in
>> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20210502110050.324953-1-npiggin@gmail.com/
>>
>> Use MODULES_VADDR/MODULES_END when it exists, use VMALLOC_START/VMALLOC_END otherwise.
>>
>> I know I suggested to always define MODULES_VADDR, but maybe that's not the best solution at the end.
> Sure, let's do it like that.
>>
>> For kprobes, is there a way to re-use functions from modules.c in alloc_insn_page() ?
> Probably we can use module_alloc() then the set_memory_ functions to
> get the permissions right.
> Something like we had in v9:
> https://lore.kernel.org/linuxppc-dev/20210316031741.1004850-3-jniethe5@gmail.com/

Yes, more or less, but using module_alloc() instead of vmalloc().
And module_alloc() implies EXEC, so only the set_memory_ro() will be required.

I see no point in doing any set_memory_xxx() in free_insn_page(), because as soon as you do a 
vfree() the page is not mapped anymore so any access will lead to a fault.

Christophe