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

From: Mike Rapoport <rppt@kernel.org>
To: Hagen Paul Pfeifer <hagen@jauu.net>
Cc: Mark Rutland <mark.rutland@arm.com>,
	David Hildenbrand <david@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	linux-mm@kvack.org, Will Deacon <will@kernel.org>,
	linux-kselftest@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Christopher Lameter <cl@linux.com>,
	Idan Yaniv <idan.yaniv@ibm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Elena Reshetova <elena.reshetova@intel.com>,
	linux-arch@vger.kernel.org, Tycho Andersen <tycho@tycho.ws>,
	linux-nvdimm@lists.01.org, Shuah Khan <shuah@kernel.org>,
	x86@kernel.org, Matthew Wilcox <willy@infradead.org>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Ingo Molnar <mingo@redhat.com>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	Arnd Bergmann <arnd@arndb.de>,
	James Bottomley <jejb@linux.ibm.com>,
	Borislav Petkov <bp@alien8.de>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andy Lutomirski <luto@kernel.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Dan Williams <dan.j.williams@intel.com>,
	linux-arm-kernel@lists.infradead.org, linux-api@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	Palmer Dabbelt <palmer@dabbelt.com>,
	linux-fsdevel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v6 0/6] mm: introduce memfd_secret system call to create "secret" memory areas
Date: Wed, 4 Nov 2020 19:02:47 +0200
Message-ID: <20201104170247.GT4879@kernel.org> (raw)
In-Reply-To: <1988407921.138656.1604489953944@office.mailbox.org>

On Wed, Nov 04, 2020 at 12:39:13PM +0100, Hagen Paul Pfeifer wrote:
> > On 11/03/2020 5:30 PM Mike Rapoport <rppt@kernel.org> 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?

Yes, this will work. The processes that share the memfd_secret file
descriptor will have access to the same memory pages, pretty much like
with shared memory.

> Hagen

-- 
Sincerely yours,
Mike.

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