Subject: Re: [PATCH v4 1/2] module: add elf_check_module_arch for module specific elf arch checks

From: Nicholas Piggin <[email-masked]>
Date: Thu, 17 Jun 2021 15:21:36 +1000

Excerpts from Jessica Yu's message of June 16, 2021 10:54 pm:
> +++ Nicholas Piggin [16/06/21 11:18 +1000]:
>>Excerpts from Jessica Yu's message of June 15, 2021 10:17 pm:
>>> +++ Nicholas Piggin [15/06/21 12:05 +1000]:
>>>>Excerpts from Jessica Yu's message of June 14, 2021 10:06 pm:
>>>>> +++ Nicholas Piggin [11/06/21 19:39 +1000]:
>>>>>>The elf_check_arch() function is used to test usermode binaries, but
>>>>>>kernel modules may have more specific requirements. powerpc would like
>>>>>>to test for ABI version compatibility.
>>>>>>
>>>>>>Add an arch-overridable function elf_check_module_arch() that defaults
>>>>>>to elf_check_arch() and use it in elf_validity_check().
>>>>>>
>>>>>>Signed-off-by: Michael Ellerman <[email-masked]>
>>>>>>[np: split patch, added changelog]
>>>>>>Signed-off-by: Nicholas Piggin <[email-masked]>
>>>>>>---
>>>>>> include/linux/moduleloader.h | 5 +++++
>>>>>> kernel/module.c              | 2 +-
>>>>>> 2 files changed, 6 insertions(+), 1 deletion(-)
>>>>>>
>>>>>>diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h
>>>>>>index 9e09d11ffe5b..fdc042a84562 100644
>>>>>>--- a/include/linux/moduleloader.h
>>>>>>+++ b/include/linux/moduleloader.h
>>>>>>@@ -13,6 +13,11 @@
>>>>>>  * must be implemented by each architecture.
>>>>>>  */
>>>>>>
>>>>>>+// Allow arch to optionally do additional checking of module ELF header
>>>>>>+#ifndef elf_check_module_arch
>>>>>>+#define elf_check_module_arch elf_check_arch
>>>>>>+#endif
>>>>>
>>>>> Hi Nicholas,
>>>>>
>>>>> Why not make elf_check_module_arch() consistent with the other
>>>>> arch-specific functions? Please see module_frob_arch_sections(),
>>>>> module_{init,exit}_section(), etc in moduleloader.h. That is, they are
>>>>> all __weak functions that are overridable by arches. We can maybe make
>>>>> elf_check_module_arch() a weak symbol, available for arches to
>>>>> override if they want to perform additional elf checks. Then we don't
>>>>> have to have this one-off #define.
>>>>
>>>>
>>>>Like this? I like it. Good idea.
>>>
>>> Yeah! Also, maybe we can alternatively make elf_check_module_arch() a
>>> separate check entirely so that the powerpc implementation doesn't
>>> have to include that extra elf_check_arch() call. Something like this maybe?
>>
>>Yeah we can do that. Would you be okay if it goes via powerpc tree? If
>>yes, then we should get your Ack (or SOB because it seems to be entirely
>>your patch now :D)
> 
> This can go through the powerpc tree. Will you do another respin
> of this patch? And yes, feel free to take my SOB for this one -
> 
>      Signed-off-by: Jessica Yu <[email-masked]>

You're maintainer so let's go with your preference. We can always adjust 
the arch hooks later if a need comes up. And yes I'll re post with you 
cc'ed.

Thanks,
Nick