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

[Hagen Paul Pfeifer]

> On 11/03/2020 5:30 PM Mike Rapoport <rppt@xxxxxxxxxx> wrote:
> 
> > > As long as the task share the file descriptor, they can share the
> > > secretmem pages, pretty much like normal memfd.
> > 
> > Including process_vm_readv() and process_vm_writev()? Let's take a hypothetical
> > "dbus-daemon-secure" service that receives data from process A and wants to
> > copy/distribute it to data areas of N other processes. Much like dbus but without
> > SOCK_DGRAM rather direct copy into secretmem/mmap pages (ring-buffer). Should be
> > possible, right?
> 
> I'm not sure I follow you here.
> For process_vm_readv() and process_vm_writev() secremem will be only
> accessible on the local part, but not on the remote.
> So copying data to secretmem pages using process_vm_writev wouldn't
> work.

A hypothetical "dbus-daemon-secure" service will not be *process related* with communication
peers. E.g. a password-input process (reading a password into secured-memory page) will
transfer the password to dbus-daemon-secure and this service will hand-over the password to
two additional applications: a IPsec process on CPU0 und CPU1 (which itself use a
secured-memory page).

So four applications IPC chain:
 password-input -> dbus-daemon-secure -> {IPsec0, IPsec1}

- password-input: uses a secured page to read/save the password locally after reading from TTY
- dbus-daemon-secure: uses a secured page for IPC (legitimate user can write and read into the secured page)
- IPSecN has secured page to save the password locally (and probably other data as well), IPC memory is memset'ed after copy

Goal: the whole password is never saved/touched on non secured pages during IPC transfer.

Question: maybe a *file-descriptor passing* mechanism can do the trick? I.e. dbus-daemon-secure
allocates via memfd_secret/mmap secure pages and permitted processes will get the descriptor/mmaped-page
passed so they can use the pages directly?

Hagen