From: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
To: "rppt@kernel.org" <rppt@kernel.org>
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Subject: Re: [PATCH v6 3/6] mm: introduce memfd_secret system call to create "secret" memory areas
Date: Tue, 29 Sep 2020 20:06:03 +0000 [thread overview]
Message-ID: <839fbb26254dc9932dcff3c48a3a4ab038c016ea.camel@intel.com> (raw)
In-Reply-To: <20200929130602.GF2142832@kernel.org>
On Tue, 2020-09-29 at 16:06 +0300, Mike Rapoport wrote:
> On Tue, Sep 29, 2020 at 04:58:44AM +0000, Edgecombe, Rick P wrote:
> > On Thu, 2020-09-24 at 16:29 +0300, Mike Rapoport wrote:
> > > Introduce "memfd_secret" 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 memfd_secret()
> > > 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.
> >
> > Seems like there were some concerns raised around direct map
> > efficiency, but in case you are going to rework this...how does
> > this
> > memory work for the existing kernel functionality that does things
> > like
> > this?
> >
> > get_user_pages(, &page);
> > ptr = kmap(page);
> > foo = *ptr;
> >
> > Not sure if I'm missing something, but I think apps could cause the
> > kernel to access a not-present page and oops.
>
> The idea is that this memory should not be accessible by the kernel,
> so
> the sequence you describe should indeed fail.
>
> Probably oops would be to noisy and in this case the report needs to
> be
> less verbose.
I was more concerned that it could cause kernel instabilities.
I see, so it should not be accessed even at the userspace address? I
wonder if it should be prevented somehow then. At least
get_user_pages() should be prevented I think. Blocking copy_*_user()
access might not be simple.
I'm also not so sure that a user would never have any possible reason
to copy data from this memory into the kernel, even if it's just
convenience. In which case a user setup could break if a specific
kernel implementation switched to get_user_pages()/kmap() from using
copy_*_user(). So seems maybe a bit thorny without fully blocking
access from the kernel, or deprecating that pattern.
You should probably call out these "no passing data to/from the kernel"
expectations, unless I missed them somewhere.
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next prev parent reply other threads:[~2020-09-29 20:06 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-24 13:28 [PATCH v6 0/6] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2020-09-24 13:28 ` [PATCH v6 1/6] mm: add definition of PMD_PAGE_ORDER Mike Rapoport
2020-09-24 13:29 ` [PATCH v6 2/6] mmap: make mlock_future_check() global Mike Rapoport
2020-09-24 13:29 ` [PATCH v6 3/6] mm: introduce memfd_secret system call to create "secret" memory areas Mike Rapoport
2020-09-29 4:58 ` Edgecombe, Rick P
2020-09-29 13:06 ` Mike Rapoport
2020-09-29 20:06 ` Edgecombe, Rick P [this message]
2020-09-30 10:35 ` Mike Rapoport
2020-09-30 20:11 ` Edgecombe, Rick P
2020-10-11 9:42 ` Mike Rapoport
2020-09-24 13:29 ` [PATCH v6 4/6] arch, mm: wire up memfd_secret system call were relevant Mike Rapoport
2020-09-24 13:29 ` [PATCH v6 5/6] mm: secretmem: use PMD-size pages to amortize direct map fragmentation Mike Rapoport
2020-09-25 7:41 ` Peter Zijlstra
2020-09-25 9:00 ` David Hildenbrand
2020-09-25 9:50 ` Peter Zijlstra
2020-09-25 10:31 ` Mark Rutland
2020-09-25 14:57 ` Tycho Andersen
2020-09-29 14:04 ` Mike Rapoport
2020-09-29 13:07 ` Mike Rapoport
2020-09-29 13:06 ` Mike Rapoport
2020-09-29 13:05 ` Mike Rapoport
2020-09-29 14:12 ` Peter Zijlstra
2020-09-29 14:31 ` Dave Hansen
2020-09-29 14:58 ` Mike Rapoport
2020-09-29 15:15 ` Peter Zijlstra
2020-09-30 10:27 ` Mike Rapoport
2020-09-30 14:39 ` James Bottomley
2020-09-30 14:45 ` David Hildenbrand
2020-09-30 15:17 ` James Bottomley
2020-09-30 15:25 ` David Hildenbrand
2020-09-30 15:09 ` Matthew Wilcox
2020-10-01 8:14 ` Mike Rapoport
2020-09-29 15:03 ` James Bottomley
2020-09-30 10:20 ` Mike Rapoport
2020-09-30 10:43 ` Peter Zijlstra
2020-09-24 13:29 ` [PATCH v6 6/6] secretmem: test: add basic selftest for memfd_secret(2) Mike Rapoport
2020-09-24 13:35 ` [PATCH] man2: new page describing memfd_secret() system call Mike Rapoport
2020-09-24 14:55 ` Alejandro Colomar
2020-10-03 9:32 ` Alejandro Colomar
2020-10-05 7:32 ` Mike Rapoport
2020-11-16 21:01 ` [PATCH v2] memfd_secret.2: New " Alejandro Colomar
2020-11-17 6:26 ` Mike Rapoport
2020-09-25 2:34 ` [PATCH v6 0/6] mm: introduce memfd_secret system call to create "secret" memory areas Andrew Morton
2020-09-25 6:42 ` Mike Rapoport
2020-11-01 11:09 ` Hagen Paul Pfeifer
2020-11-02 15:40 ` Mike Rapoport
2020-11-03 13:52 ` Hagen Paul Pfeifer
2020-11-03 16:30 ` Mike Rapoport
2020-11-04 11:39 ` Hagen Paul Pfeifer
2020-11-04 17:02 ` Mike Rapoport
2020-11-09 10:41 ` Hagen Paul Pfeifer
2020-11-02 9:11 ` David Hildenbrand
2020-11-02 9:31 ` David Hildenbrand
2020-11-02 17:43 ` Mike Rapoport
2020-11-02 17:51 ` David Hildenbrand
2020-11-03 9:52 ` Mike Rapoport
2020-11-03 10:11 ` David Hildenbrand
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