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From: Arnd Bergmann <arnd@arndb.de>
To: Mike Rapoport <rppt@kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Christopher Lameter <cl@linux.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Elena Reshetova <elena.reshetova@intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Idan Yaniv <idan.yaniv@ibm.com>,
	Ingo Molnar <mingo@redhat.com>,
	James Bottomley <jejb@linux.ibm.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Matthew Wilcox <willy@infradead.org>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tycho Andersen <tycho@tycho.ws>, Will Deacon <will@kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	linux-nvdimm@lists.01.org,
	linux-riscv <linux-riscv@lists.infradead.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	linaro-mm-sig@lists.linaro.org,
	Sumit Semwal <sumit.semwal@linaro.org>
Subject: Re: [PATCH 3/6] mm: introduce secretmemfd system call to create "secret" memory areas
Date: Mon, 20 Jul 2020 16:34:12 +0200	[thread overview]
Message-ID: <CAK8P3a07jAec4hKyNMcha032TT6OXjYHaZZ4Za9ncDsvapeg8Q@mail.gmail.com> (raw)
In-Reply-To: <20200720142053.GC8593@kernel.org>

On Mon, Jul 20, 2020 at 4:21 PM Mike Rapoport <rppt@kernel.org> wrote:
> On Mon, Jul 20, 2020 at 01:30:13PM +0200, Arnd Bergmann wrote:
> > On Mon, Jul 20, 2020 at 11:25 AM Mike Rapoport <rppt@kernel.org> wrote:
> > >
> > > From: Mike Rapoport <rppt@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);
> > >         ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED,
> > >                    fd, 0);
> > >
> > > Signed-off-by: Mike Rapoport <rppt@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.
>
> TBH, I didn't think about dmabuf, but my undestanding is that is this
> case memory areas are not visible to the OS because they are on device
> memory rather than normal RAM and when dmabuf is backed by the normal
> RAM, the memory is visible to the OS.

No, dmabuf is normally about normal RAM that is shared between multiple
devices, the idea is that you can have one driver allocate a buffer in RAM
and export it to user space through a file descriptor. The application can then
go and mmap() it or pass it into one or more other drivers.

This can be used e.g. for sharing a buffer between a video codec and the
gpu, or between a crypto engine and another device that accesses
unencrypted data while software can only observe the encrypted version.

       Arnd

  reply	other threads:[~2020-07-20 14:34 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-20  9:24 [PATCH 0/6] " Mike Rapoport
2020-07-20  9:24 ` [PATCH 1/6] mm: add definition of PMD_PAGE_ORDER Mike Rapoport
2020-07-20  9:24 ` [PATCH 2/6] mmap: make mlock_future_check() global Mike Rapoport
2020-07-20  9:24 ` [PATCH 3/6] mm: introduce secretmemfd system call to create "secret" memory areas Mike Rapoport
2020-07-20 11:30   ` Arnd Bergmann
2020-07-20 14:20     ` Mike Rapoport
2020-07-20 14:34       ` Arnd Bergmann [this message]
2020-07-20 17:46         ` Mike Rapoport
2020-07-20 15:51     ` James Bottomley
2020-07-20 18:08       ` Arnd Bergmann
2020-07-20 19:16         ` James Bottomley
2020-07-20 20:05           ` Arnd Bergmann
2020-07-21 10:59   ` Michael Kerrisk (man-pages)
2020-07-20  9:24 ` [PATCH 4/6] arch, mm: wire up secretmemfd system call were relevant Mike Rapoport
2020-07-26 17:44   ` Palmer Dabbelt
2020-07-20  9:24 ` [PATCH 5/6] mm: secretmem: use PMD-size pages to amortize direct map fragmentation Mike Rapoport
2020-07-20  9:24 ` [PATCH 6/6] mm: secretmem: add ability to reserve memory at boot Mike Rapoport

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