Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings

Andy Lutomirski
2019-10-28T20:45:28Z

> On Oct 27, 2019, at 4:17 AM, Mike Rapoport <rppt@kernel.org> wrote:
>
> ﻿From: Mike Rapoport <rppt@linux.ibm.com>
>
> Hi,
>
> The patch below aims to allow applications to create mappins that have
> pages visible only to the owning process. Such mappings could be used to
> store secrets so that these secrets are not visible neither to other
> processes nor to the kernel.
>
> I've only tested the basic functionality, the changes should be verified
> against THP/migration/compaction. Yet, I'd appreciate early feedback.

I’ve contemplated the concept a fair amount, and I think you should consider a change to the API. In particular, rather than having it be a MAP_ flag, make it a chardev. You can, at least at first, allow only MAP_SHARED, and admins can decide who gets to use it. It might also play better with the VM overall, and you won’t need a VM_ flag for it — you can just wire up .fault to do the right thing.