Re: [PATCH v6 0/6] mm: introduce memfd_secret system call to create "secret" memory areas

[Andrew Morton]

On Thu, 24 Sep 2020 16:28:58 +0300 Mike Rapoport <rppt@xxxxxxxxxx> wrote:

> From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> 
> 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].

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?