On Mon, Jul 20, 2020 at 11:25 AM Mike Rapoport [off-list ref] wrote:

From: Mike Rapoport <redacted>

Introduce "secretmemfd" system call with the ability to create memory areas
visible only in the context of the owning process and not mapped not only
to other processes but in the kernel page tables as well.

The user will create a file descriptor using the secretmemfd system call
where flags supplied as a parameter to this system call will define the
desired protection mode for the memory associated with that file
descriptor. Currently there are two protection modes:

* exclusive - the memory area is unmapped from the kernel direct map and it
              is present only in the page tables of the owning mm.
* uncached  - the memory area is present only in the page tables of the
              owning mm and it is mapped there as uncached.

For instance, the following example will create an uncached mapping (error
handling is omitted):

        fd = secretmemfd(SECRETMEM_UNCACHED);
        ftruncate(fd, MAP_SIZE);
        ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED,
                   fd, 0);

Signed-off-by: Mike Rapoport <redacted>

I wonder if this should be more closely related to dmabuf file
descriptors, which
are already used for a similar purpose: sharing access to secret memory areas
that are not visible to the OS but can be shared with hardware through device
drivers that can import a dmabuf file descriptor.

      Arnd