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Re: [PATCH v2] futex: mark get_robust_list as deprecated

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On 03/30/2012 09:05 AM, Matt Helsley wrote:
> On Fri, Mar 23, 2012 at 03:06:02PM -0700, Eric W. Biederman wrote:
>> Kees Cook <keescook@xxxxxxxxxxxx> writes:
>>
>>> Notify get_robust_list users that the syscall is going away.
>>
>> Has anyone asked the question if the folks working on checkpoint/restart
>> are going to need this.
>>
>> This seems like important information to know if you want to checkpoint
>> a process.
> 
> I have no idea if the CRIU and DMTCP folks care about this. I've added
> some folks related to those projects to the Cc list.

Nope, we don't need this syscall, thanks for notifying!

>>
>> Eric
>>
>>> Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>>> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
>>> ---
>>> v2:
>>>  - add note to feature-removal-schedule.txt.
>>> ---
>>>  Documentation/feature-removal-schedule.txt |   10 ++++++++++
>>>  kernel/futex.c                             |    2 ++
>>>  kernel/futex_compat.c                      |    2 ++
>>>  3 files changed, 14 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
>>> index 4bfd982..e3bf119 100644
>>> --- a/Documentation/feature-removal-schedule.txt
>>> +++ b/Documentation/feature-removal-schedule.txt
>>> @@ -543,3 +543,13 @@ When:	3.5
>>>  Why:	The old kmap_atomic() with two arguments is deprecated, we only
>>>  	keep it for backward compatibility for few cycles and then drop it.
>>>  Who:	Cong Wang <amwang@xxxxxxxxxx>
>>> +
>>> +----------------------------
>>> +
>>> +What:	get_robust_list syscall
>>> +When:	2013
>>> +Why:	There appear to be no production users of the get_robust_list syscall,
>>> +	and it runs the risk of leaking address locations, allowing the bypass
>>> +	of ASLR. It was only ever intended for debugging, so it should be
>>> +	removed.
> 
> So I've looked in glibc, gdb, and DMTCP. The description of the intended
> use of get_robust_list() is accurate. However the benefit of ASLR is
> less clear when it comes to the robust list. In glibc the robust list is
> only used from NPTL. The robust list head is in struct pthread which can be
> obtained from pthread_self() anyway. Thus I think ASLR doesn't really help
> obfuscate the robust futex list unless the program is using robust futexes
> without the aid of glibc.
> 
> Cheers,
> 	-Matt Helsley
> 
> .
> 

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