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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: "Tomasz Figa" <tfiga@chromium.org>,
	"Marek Szyprowski" <m.szyprowski@samsung.com>,
	"DRI Development" <dri-devel@lists.freedesktop.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Daniel Vetter" <daniel.vetter@intel.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"John Hubbard" <jhubbard@nvidia.com>,
	"Jérôme Glisse" <jglisse@redhat.com>, "Jan Kara" <jack@suse.cz>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Linux MM" <linux-mm@kvack.org>,
	"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
	"Pawel Osciak" <pawel@osciak.com>,
	"Kyungmin Park" <kyungmin.park@samsung.com>,
	"Inki Dae" <inki.dae@samsung.com>,
	"Joonyoung Shim" <jy0922.shim@samsung.com>,
	"Seung-Woo Kim" <sw0312.kim@samsung.com>,
	linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
	"open list:DMA BUFFER SHARING FRAMEWORK"
	<linux-media@vger.kernel.org>,
	"Oded Gabbay" <oded.gabbay@gmail.com>
Subject: Re: [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM
Date: Wed, 7 Oct 2020 10:06:10 -0300	[thread overview]
Message-ID: <20201007130610.GP5177@ziepe.ca> (raw)
In-Reply-To: <CAKMK7uG3fds79Yf9VhMstnJ2+UHYUEVdODkoOvtwFC28_+T6RA@mail.gmail.com>

On Wed, Oct 07, 2020 at 02:58:33PM +0200, Daniel Vetter wrote:
> On Wed, Oct 7, 2020 at 2:48 PM Tomasz Figa <tfiga@chromium.org> wrote:
> >
> > On Wed, Oct 7, 2020 at 2:44 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > >
> > > On Wed, Oct 07, 2020 at 02:33:56PM +0200, Marek Szyprowski wrote:
> > > > Well, it was in vb2_get_vma() function, but now I see that it has been
> > > > lost in fb639eb39154 and 6690c8c78c74 some time ago...
> > >
> > > There is no guarentee that holding a get on the file says anthing
> > > about the VMA. This needed to check that the file was some special
> > > kind of file that promised the VMA layout and file lifetime are
> > > connected.
> > >
> > > Also, cloning a VMA outside the mm world is just really bad. That
> > > would screw up many assumptions the drivers make.
> > >
> > > If it is all obsolete I say we hide it behind a default n config
> > > symbol and taint the kernel if anything uses it.
> > >
> > > Add a big comment above the follow_pfn to warn others away from this
> > > code.
> >
> > Sadly it's just verbally declared as deprecated and not formally noted
> > anyway. There are a lot of userspace applications relying on user
> > pointer support.
> 
> userptr can stay, it's the userptr abuse for zerocpy buffer sharing
> which doesn't work anymore. At least without major surgery (you'd need
> an mmu notifier to zap mappings and recreate them, and that pretty
> much breaks the v4l model of preallocating all buffers to make sure we
> never underflow the buffer queue). And static mappings are not coming
> back I think, we'll go ever more into the direction of dynamic
> mappings and moving stuff around as needed.

Right, and to be clear, the last time I saw a security flaw of this
magnitude from a subsystem badly mis-designing itself, Linus's
knee-jerk reaction was to propose to remove the whole subsystem.

Please don't take status-quo as acceptable, V4L community has to work
to resolve this, uABI breakage or not. The follow_pfn related code
must be compiled out of normal distro kernel builds.

Jason


  reply	other threads:[~2020-10-07 13:06 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-02 17:53 [PATCH 1/2] mm/frame-vec: Drop gup_flags from get_vaddr_frames() Daniel Vetter
2020-10-02 17:53 ` [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM Daniel Vetter
2020-10-02 18:06   ` Jason Gunthorpe
2020-10-02 18:16     ` Daniel Vetter
2020-10-02 23:31       ` Jason Gunthorpe
2020-10-03  8:34         ` Oded Gabbay
2020-10-03  9:40         ` Daniel Vetter
2020-10-04 12:50           ` Jason Gunthorpe
2020-10-04 16:09             ` Daniel Vetter
2020-10-05 17:28               ` Jason Gunthorpe
2020-10-05 18:16                 ` Daniel Vetter
2020-10-05 18:37                   ` Jason Gunthorpe
2020-10-05 18:54                     ` Daniel Vetter
2020-10-05 22:43                       ` Daniel Vetter
2020-10-05 23:41                         ` Jason Gunthorpe
2020-10-06  6:23                           ` Daniel Vetter
2020-10-06 12:26                             ` Jason Gunthorpe
2020-10-06 13:08                               ` Daniel Vetter
2020-10-07 10:47           ` Marek Szyprowski
2020-10-07 12:01             ` Daniel Vetter
2020-10-07 12:33               ` Marek Szyprowski
2020-10-07 12:44                 ` Jason Gunthorpe
2020-10-07 12:47                   ` Tomasz Figa
2020-10-07 12:58                     ` Daniel Vetter
2020-10-07 13:06                       ` Jason Gunthorpe [this message]
2020-10-07 13:34                         ` Tomasz Figa
2020-10-07 13:42                           ` Jason Gunthorpe
2020-10-07 14:08                           ` Daniel Vetter
2020-10-07 14:11                             ` Tomasz Figa
2020-10-07 14:22                               ` Daniel Vetter
2020-10-07 15:05                                 ` Tomasz Figa
2020-10-07 14:58                               ` Jason Gunthorpe
2020-10-07 13:06         ` Tomasz Figa
2020-10-07 13:14           ` Jason Gunthorpe
2020-10-05 15:03     ` Jan Kara
2020-10-02 22:39   ` John Hubbard
2020-10-03  9:45     ` Daniel Vetter
2020-10-03 22:52       ` John Hubbard
2020-10-03 23:24         ` Jason Gunthorpe
2020-10-04 11:20           ` Daniel Vetter
2020-10-05 17:35             ` Jason Gunthorpe
2020-10-02 18:22 ` [PATCH 1/2] mm/frame-vec: Drop gup_flags from get_vaddr_frames() Tomasz Figa
2020-10-02 19:21   ` Oded Gabbay
2020-10-05 17:38 [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM Jason Gunthorpe
2020-10-05 17:47 ` Jason Gunthorpe
2020-10-06  3:36   ` Andrew Morton
2020-10-06 11:57     ` Jason Gunthorpe
2020-10-05 17:53 ` Jan Kara
2020-10-05 17:57   ` Jason Gunthorpe
2020-10-05 18:16     ` Daniel Vetter
2020-10-06 11:56     ` Daniel Vetter

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