[PATCH 3/6] mm: introduce secretmemfd system call to create "secret" memory areas

Arnd Bergmann arnd at arndb.de
Mon Jul 20 07:30:13 EDT 2020

On Mon, Jul 20, 2020 at 11:25 AM Mike Rapoport <rppt at kernel.org> wrote:
> From: Mike Rapoport <rppt at linux.ibm.com>
> 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);
>                    fd, 0);
> Signed-off-by: Mike Rapoport <rppt at linux.ibm.com>

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.


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