Re: [PATCH v6 19/20] elf: Fix runtime linker auditing on aarch64 (BZ #26643)

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 21/12/2021 11:44, Florian Weimer wrote:
> * Adhemerval Zanella:
> 
>> On 20/12/2021 18:32, Florian Weimer wrote:
>>> * Adhemerval Zanella:
>>>
>>>> diff --git a/elf/rtld.c b/elf/rtld.c
>>>> index 29a37f51d3..1a13ae6314 100644
>>>> --- a/elf/rtld.c
>>>> +++ b/elf/rtld.c
>>>> @@ -990,10 +990,10 @@ file=%s [%lu]; audit interface function la_version returned zero; ignored.\n",
>>>>        return;
>>>>      }
>>>>  
>>>> -  if (lav > LAV_CURRENT)
>>>> +  if (lav != LAV_CURRENT)
>>>>      {
>>>>        _dl_debug_printf ("\
>>>> -ERROR: audit interface '%s' requires version %d (maximum supported version %d); ignored.\n",
>>>> +ERROR: audit interface '%s' requires version %d (current supported version %d); ignored.\n",
>>>>  			name, lav, LAV_CURRENT);
>>>>        unload_audit_module (dlmargs.map, original_tls_idx);
>>>>        return;
>>>
>>> Sorry, this is not what I had in mind.  I'd like to increase LAV_CURRENT
>>> and pretend that the old and new versions have the same behavior, at
>>> least as far as aarch64 is concerned.  We need not write the
>>> compatibility code for the old <link.h> at this time, only if there
>>> actual users out there that demand it.
>>
>> Do you mean to only check if lav >= LAV_CURRENT and allow old audit modules
>> as well?
> 
> Yes.
> 
>> At least for aarch64 old audit modules are error-prone and potentially adds
>> more subtle issues since they do not save/restore some return register that
>> I don't see any real gain to keep supporting them.
> 
> I disagree.  la_objsearch alone is a significant use case, and I don't
> see why it wouldn't work today.  It does not need any
> architecture-specific code whatsoever.

My main problem is provide a API which undocumented and missing support
where if users tries to replicate what other architecture does it will
shoot in the foot.  I think this is just a broken API and we should
avoid it.