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

On Oct 27, 2019, at 4:17 AM, Mike Rapoport [off-list ref] wrote:

From: Mike Rapoport [off-list ref]

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.