On Thu, Sep 24, 2020 at 07:34:28PM -0700, Andrew Morton wrote:

On Thu, 24 Sep 2020 16:28:58 +0300 Mike Rapoport [off-list ref] wrote:

quoted

From: Mike Rapoport <redacted>

Hi,

This is an implementation of "secret" mappings backed by a file descriptor. 
I've dropped the boot time reservation patch for now as it is not strictly
required for the basic usage and can be easily added later either with or
without CMA.

...

The file descriptor backing secret memory mappings is created using a
dedicated memfd_secret system call The desired protection mode for the
memory is configured using flags parameter of the system call. The mmap()
of the file descriptor created with memfd_secret() will create a "secret"
memory mapping. The pages in that mapping will be marked as not present in
the direct map and will have desired protection bits set in the user page
table. For instance, current implementation allows uncached mappings.

Although normally Linux userspace mappings are protected from other users, 
such secret mappings are useful for environments where a hostile tenant is
trying to trick the kernel into giving them access to other tenants
mappings.

Additionally, the secret mappings may be used as a mean to protect guest
memory in a virtual machine host.

For demonstration of secret memory usage we've created a userspace library
[1] that does two things: the first is act as a preloader for openssl to

I can find no [1].

Oops, sorry. It's

https://git.kernel.org/pub/scm/linux/kernel/git/jejb/secret-memory-preloader.git/

I'm not a fan of the enumerated footnote thing.  Why not inline the url
right here so readers don't need to jump around?

-- 
Sincerely yours,
Mike.