Re: Library auditing interface stability?

[Carlos O'Donell <carlos at redhat dot com>]

On 05/05/2016 05:29 PM, Steven Munroe wrote:
> On Thu, 2016-05-05 at 11:57 -0400, Carlos O'Donell wrote:
>> On 05/05/2016 10:56 AM, Steven Munroe wrote:
>>> On Thu, 2016-04-28 at 15:21 -0400, Carlos O'Donell wrote:
>>>> On 04/28/2016 04:20 AM, Florian Weimer wrote:
>>>>> On 04/20/2016 04:24 PM, Ulrich Drepper wrote:
>>>>>> On Tue, Apr 19, 2016 at 5:03 PM, Carlos O'Donell
>>>>>> <carlos@redhat.com> wrote:
>>>>>>> In particular the La_*_regs and La_*_retval which contains 
>>>>>>> additional registers as we expand the supported ISAs.
>>>>>>
>>>>>> la_version is there to preserve unlimited backward compatibility.
>>>>>
>>>>> We have not used this mechanism when we added support for additional
>>>>> registers to be passed to the PLT callbacks.  Looking at commits
>>>>> 14c5cbabc2d11004ab223ae5eae761ddf83ef99e and 
>>>>> 5cdd1989d1d2f135d02e66250f37ba8e767f9772, there is no way for an
>>>>> audit module to notice if these additional fields are maintained by
>>>>> glibc.
>>>>
>>>> I think we should have bumped the la_version number for all changes
>>>> to the structure for any architecture.
>>>>
>>>> Do we fix this by bumping LAV_CURRENT?
>>>>
>>>> diff --git a/elf/link.h b/elf/link.h
>>>> index f448141..cbf94a3 100644
>>>> --- a/elf/link.h
>>>> +++ b/elf/link.h
>>>> @@ -95,8 +95,13 @@ struct link_map
>>>>
>>>>  #ifdef __USE_GNU
>>>>
>>>> -/* Version numbers for la_version handshake interface.  */
>>>> -#define LAV_CURRENT    1
>>>> +/* Version numbers for la_version handshake interface.
>>>> +   1 - Initial implementation.
>>>> +   2 - Added lrv_bnd0 and lrv_bnd1 to La_i86_retval.
>>>> +   3 - Added lr_v[24,25,26,27,28,29,30,31] to La_s390_64_regs, and
>>>> +       La_s390_32_regs. Added lrv_v24 to La_s390_64_retval and
>>>> +       La_s390_64_retval.  */
>>>> +#define LAV_CURRENT    3
>>>>
>>>>  /* Activity types signaled through la_activity.  */
>>>>  enum
>>>> ---
>>>>
>>>> We can't fix audit modules in the field which return 1.
>>>>
>>>> We can fix newly compiled audit modules, making them expect
>>>> a LAV_CURRENT of 3, such that they can't be run with older
>>>> LAV_CURRENT 1 glibc which doesn't have BIND on x86 or
>>>> VSX on s390?
>>>>
>>>
>>> I am not sure if the audit modules need to now or care about PPC VSX or
>>> TAR, but if memory serves. VSX was added after the audit API.
>>
>> Is VSX or TAR part of the procedure call sequence?
>>
>> The La_*_regs structure allows an audit module to modify incoming
>> registers to the function using the PLT hook being provided by the
>> audit infrastructure.
>>
> Not VSX or TAR but VMX regs are, which GLIBC was library audit
> added? ...

Library auditing has been in place since glibc 2.4 (2006-03-06).

When architectures add new registers which are used in a procedure call
they should also add them to the auditing interface (otherwise auditors
can't inspect them) and they also need to be saved/restored to/from the
auditing data structures.

It might be a rare enough situation that nobody has noticed that those
specific registers are not in the interface.

Could someone from IBM audit sysdeps/powerpc/bits/link.h to see what's
missing for ppc and ppc64?

-- 
Cheers,
Carlos.