On Thu, Feb 11, 2021 at 01:07:10PM +0100, David Hildenbrand wrote:

On 11.02.21 12:27, Mike Rapoport wrote:

quoted

On Thu, Feb 11, 2021 at 10:01:32AM +0100, David Hildenbrand wrote:

So let's talk about the main user-visible differences to other memfd files
(especially, other purely virtual files like hugetlbfs). With secretmem:

- File content can only be read/written via memory mappings.
- File content cannot be swapped out.

I think there are still valid ways to modify file content using syscalls:
e.g., fallocate(PUNCH_HOLE). Things like truncate also seems to work just
fine.

 
These work perfectly with any file, so maybe we should have added
memfd_create as a flag to open(2) back then and now the secretmem file
descriptors?
 

quoted

quoted

AFAIKS, we would need MFD_SECRET and disallow
MFD_ALLOW_SEALING and MFD_HUGETLB.

So here we start to multiplex.

Yes. And as Michal said, maybe we can support combinations in the future.

Isn't there a general agreement that syscall multiplexing is not a good
thing?
memfd_create already has flags validation that does not look very nice.
Adding there only MFD_SECRET will make it a bit less nice, but when we'll
grow new functionality into secretmem that will become horrible.
 
-- 
Sincerely yours,
Mike.

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