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From: Mike Rapoport <rppt@kernel.org>
To: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Cc: "mark.rutland@arm.com" <mark.rutland@arm.com>,
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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 16:06:02 +0300
Message-ID: <20200929130602.GF2142832@kernel.org> (raw)
In-Reply-To: <d466e1f13ff615332fe1f513f6c1d763db28bd9a.camel@intel.com>

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.

-- 
Sincerely yours,
Mike.

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Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-24 13:28 [PATCH v6 0/6] " 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 [this message]
2020-09-29 20:06       ` Edgecombe, Rick P
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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