Re: [PATCH v7 01/14] mm: Add F_SEAL_AUTO_ALLOCATE seal to memfd

David Hildenbrand
2022-08-05T18:06:12Z

On 05.08.22 19:55, Paolo Bonzini wrote:
> On 7/21/22 11:44, David Hildenbrand wrote:
>>
>> Also, I*think* you can place pages via userfaultfd into shmem. Not
>> sure if that would count "auto alloc", but it would certainly bypass
>> fallocate().
>
> Yeah, userfaultfd_register would probably have to forbid this for
> F_SEAL_AUTO_ALLOCATE vmas. Maybe the memfile_node can be reused for
> this, adding a new MEMFILE_F_NO_AUTO_ALLOCATE flags? Then
> userfault_register would do something like
> memfile_node_get_flags(vma->vm_file) and check the result.

An alternative is to simply have the shmem allocation fail in a similar
way. Maybe it does already, I haven't checked (don't think so).

--
Thanks,

David / dhildenb