Re: pkeys on POWER: Access rights not reset on execve

[Florian Weimer <fweimer@redhat.com>]

On 06/04/2018 09:02 PM, Ram Pai wrote:
> On Mon, Jun 04, 2018 at 07:57:46PM +0200, Florian Weimer wrote:
>> On 06/04/2018 04:01 PM, Ram Pai wrote:
>>> On Mon, Jun 04, 2018 at 12:12:07PM +0200, Florian Weimer wrote:
>>>> On 06/03/2018 10:18 PM, Ram Pai wrote:
>>>>> On Mon, May 21, 2018 at 01:29:11PM +0200, Florian Weimer wrote:
>>>>>> On 05/20/2018 09:11 PM, Ram Pai wrote:
>>>>>>> Florian,
>>>>>>>
>>>>>>> 	Does the following patch fix the problem for you?  Just like x86
>>>>>>> 	I am enabling all keys in the UAMOR register during
>>>>>>> 	initialization itself. Hence any key created by any thread at
>>>>>>> 	any time, will get activated on all threads. So any thread
>>>>>>> 	can change the permission on that key. Smoke tested it
>>>>>>> 	with your test program.
>>>>>>
>>>>>> I think this goes in the right direction, but the AMR value after
>>>>>> fork is still strange:
>>>>>>
>>>>>> AMR (PID 34912): 0x0000000000000000
>>>>>> AMR after fork (PID 34913): 0x0000000000000000
>>>>>> AMR (PID 34913): 0x0000000000000000
>>>>>> Allocated key in subprocess (PID 34913): 2
>>>>>> Allocated key (PID 34912): 2
>>>>>> Setting AMR: 0xffffffffffffffff
>>>>>> New AMR value (PID 34912): 0x0fffffffffffffff
>>>>>> About to call execl (PID 34912) ...
>>>>>> AMR (PID 34912): 0x0fffffffffffffff
>>>>>> AMR after fork (PID 34914): 0x0000000000000003
>>>>>> AMR (PID 34914): 0x0000000000000003
>>>>>> Allocated key in subprocess (PID 34914): 2
>>>>>> Allocated key (PID 34912): 2
>>>>>> Setting AMR: 0xffffffffffffffff
>>>>>> New AMR value (PID 34912): 0x0fffffffffffffff
>>>>>>
>>>>>> I mean this line:
>>>>>>
>>>>>> AMR after fork (PID 34914): 0x0000000000000003
>>>>>>
>>>>>> Shouldn't it be the same as in the parent process?
>>>>>
>>>>> Fixed it. Please try this patch. If it all works to your satisfaction, I
>>>>> will clean it up further and send to Michael Ellermen(ppc maintainer).
>>>>>
>>>>>
>>>>> commit 51f4208ed5baeab1edb9b0f8b68d7144449b3527
>>>>> Author: Ram Pai <linuxram@us.ibm.com>
>>>>> Date:   Sun Jun 3 14:44:32 2018 -0500
>>>>>
>>>>>      Fix for the fork bug.
>>>>>      Signed-off-by: Ram Pai <linuxram@us.ibm.com>
>>>>
>>>> Is this on top of the previous patch, or a separate fix?
>>>
>>> top of previous patch.
>>
>> Thanks.  With this patch, I get this on an LPAR:
>>
>> AMR (PID 1876): 0x0000000000000003
>> AMR after fork (PID 1877): 0x0000000000000003
>> AMR (PID 1877): 0x0000000000000003
>> Allocated key in subprocess (PID 1877): 2
>> Allocated key (PID 1876): 2
>> Setting AMR: 0xffffffffffffffff
>> New AMR value (PID 1876): 0x0fffffffffffffff
>> About to call execl (PID 1876) ...
>> AMR (PID 1876): 0x0000000000000003
>> AMR after fork (PID 1878): 0x0000000000000003
>> AMR (PID 1878): 0x0000000000000003
>> Allocated key in subprocess (PID 1878): 2
>> Allocated key (PID 1876): 2
>> Setting AMR: 0xffffffffffffffff
>> New AMR value (PID 1876): 0x0fffffffffffffff
>>
>> Test program is still this one:
>>
>> <https://lists.ozlabs.org/pipermail/linuxppc-dev/2018-May/173198.html>
>>
>> So the process starts out with a different AMR value for some
>> reason. That could be a pre-existing bug that was just hidden by the
>> reset-to-zero on fork, or it could be intentional.  But the kernel
> 
> yes it is a bug, a patch for which is lined up for submission..
> 
> The fix is
> 
> 
> commit eaf5b2ac002ad2f5bca118d7ce075ce28311aa8e
> Author: Ram Pai <linuxram@us.ibm.com>
> Date:   Mon Jun 4 10:58:44 2018 -0500
> 
>      powerpc/pkeys: fix total pkeys calculation
>      
>      Total number of pkeys calculation is off by 1. Fix it.
>      
>      Signed-off-by: Ram Pai <linuxram@us.ibm.com>

Looks good to me now.  Initial AMR value is zero, as is currently intended.

So the remaining question at this point is whether the Intel behavior 
(default-deny instead of default-allow) is preferable.

But if you can get the existing fixes into 4.18 and perhaps the relevant 
stable kernels, that would already be a great help for my glibc work.

Thanks,
Florian