Re: [PATCH v3 0/6] vdso/datastore: Allow prefaulting by mlockall()

[David Hildenbrand (Arm)]

On 6/3/26 14:47, Thomas Weißschuh wrote:
> On Wed, Jun 03, 2026 at 01:35:19PM +0200, David Hildenbrand (Arm) wrote:
>> On 6/3/26 12:10, Thomas Weißschuh wrote:
> 
> (...)
> 
>>>
>>> There are no side-effects, this is just global shared memory.
>>> (But as mentioned before, writes can not be allowed)
>>> Accesses from other tasks need to be prevented, which is what
>>> patch 4 tries to do based on FAULT_FLAG_REMOTE.
>>>
>>> The only data in these pages which is not globally shared and accessible
>>> are the time namespace offsets. But /proc/$PID/timens_offsets is
>>> world-readable anyways.
>>>
>>>
>>> We use VM_DONTDUMP on the VMA, shouldn't that prevent dumping?
>>> Dumping these pages is not a (security) issue, just pointless.
>>
>> Ah, right.
>>
>> So we still have
>>
>> VM_READ | VM_MAYREAD | VM_DONTDUMP | VM_MIXEDMAP ...
>>
>> So even FOLL_FORCE cannot write to it.
>>
>> It might be good to document the change (pages can not be GUP'ed, including
>> being read by ptrace etc). But I agree that it should likely be fine.
> 
> Should this "not" have been a "now"?

Yes! :)

-- 
Cheers,

David