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

[Jordan Niethe]

On Mon, May 3, 2021 at 4:22 PM Christophe Leroy
<christophe.leroy at csgroup.eu> wrote:
>
>
>
> Le 03/05/2021 à 08:16, Jordan Niethe a écrit :
> > On Mon, May 3, 2021 at 3:57 PM Christophe Leroy
> > <christophe.leroy at 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 at 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 at 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.
Yep.
>
> 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.
Yeah, I'd not realised we had VM_FLUSH_RESET_PERMS when I added that.
I agree it's pointless.
>
> Christophe