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From: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Daniel Vetter" <daniel.vetter@ffwll.ch>,
	"DRI Development" <dri-devel@lists.freedesktop.org>,
	LKML <linux-kernel@vger.kernel.org>,
	kvm@vger.kernel.org, linux-mm@kvack.org,
	linux-arm-kernel@lists.infradead.org,
	linux-samsung-soc@vger.kernel.org, linux-media@vger.kernel.org,
	linux-s390@vger.kernel.org,
	"Daniel Vetter" <daniel.vetter@intel.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"John Hubbard" <jhubbard@nvidia.com>,
	"Jérôme Glisse" <jglisse@redhat.com>, "Jan Kara" <jack@suse.cz>,
	"Linus Torvalds" <torvalds@linux-foundation.org>
Subject: Re: [PATCH v2 09/17] mm: Add unsafe_follow_pfn
Date: Fri, 9 Oct 2020 14:39:47 +0200
Message-ID: <20201009143947.751c5eb1@coco.lan> (raw)
In-Reply-To: <20201009143723.45609bfb@coco.lan>

Em Fri, 9 Oct 2020 14:37:23 +0200
Mauro Carvalho Chehab <mchehab+huawei@kernel.org> escreveu:

> Em Fri, 9 Oct 2020 09:21:11 -0300
> Jason Gunthorpe <jgg@ziepe.ca> escreveu:
> 
> > On Fri, Oct 09, 2020 at 12:34:21PM +0200, Mauro Carvalho Chehab wrote:  
> > > Hi,
> > > 
> > > Em Fri,  9 Oct 2020 09:59:26 +0200
> > > Daniel Vetter <daniel.vetter@ffwll.ch> escreveu:
> > >     
> > > > Way back it was a reasonable assumptions that iomem mappings never
> > > > change the pfn range they point at. But this has changed:
> > > > 
> > > > - gpu drivers dynamically manage their memory nowadays, invalidating
> > > > ptes with unmap_mapping_range when buffers get moved
> > > > 
> > > > - contiguous dma allocations have moved from dedicated carvetouts to
> > > > cma regions. This means if we miss the unmap the pfn might contain
> > > > pagecache or anon memory (well anything allocated with GFP_MOVEABLE)
> > > > 
> > > > - even /dev/mem now invalidates mappings when the kernel requests that
> > > > iomem region when CONFIG_IO_STRICT_DEVMEM is set, see 3234ac664a87
> > > > ("/dev/mem: Revoke mappings when a driver claims the region")
> > > > 
> > > > Accessing pfns obtained from ptes without holding all the locks is
> > > > therefore no longer a good idea.
> > > > 
> > > > Unfortunately there's some users where this is not fixable (like v4l
> > > > userptr of iomem mappings) or involves a pile of work (vfio type1
> > > > iommu). For now annotate these as unsafe and splat appropriately.
> > > > 
> > > > This patch adds an unsafe_follow_pfn, which later patches will then
> > > > roll out to all appropriate places.    
> > > 
> > > NACK, as this breaks an existing userspace API on media.    
> > 
> > It doesn't break it. You get a big warning the thing is broken and it
> > keeps working.
> > 
> > We can't leave such a huge security hole open - it impacts other
> > subsystems, distros need to be able to run in a secure mode.  
> 
> Well, if distros disable it, then apps will break.
> 
> > > While I agree that using the userptr on media is something that
> > > new drivers may not support, as DMABUF is a better way of
> > > handling it, changing this for existing ones is a big no, 
> > > as it may break usersapace.    
> > 
> > media community needs to work to fix this, not pretend it is OK to
> > keep going as-is.  
> 
> > Dealing with security issues is the one case where an uABI break might
> > be acceptable.
> > 
> > If you want to NAK it then you need to come up with the work to do
> > something here correctly that will support the old drivers without the
> > kernel taint.
> > 
> > Unfortunately making things uncomfortable for the subsystem is the big
> > hammer the core kernel needs to use to actually get this security work
> > done by those responsible.  
> 
> 
> I'm not pretending that this is ok. Just pointing that the approach
> taken is NOT OK.
> 
> I'm not a mm/ expert, but, from what I understood from Daniel's patch
> description is that this is unsafe *only if*  __GFP_MOVABLE is used.
> 
> Well, no drivers inside the media subsystem uses such flag, although
> they may rely on some infrastructure that could be using it behind
> the bars.
> 
> If this is the case, the proper fix seems to have a GFP_NOT_MOVABLE 
> flag that it would be denying the core mm code to set __GFP_MOVABLE.
> 
> Please let address the issue on this way, instead of broken an
> userspace API that it is there since 1991.

In time: I meant to say 1998.

Thanks,
Mauro

  reply index

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-09  7:59 [PATCH v2 00/17] follow_pfn and other iomap races Daniel Vetter
2020-10-09  7:59 ` [PATCH v2 01/17] drm/exynos: Stop using frame_vector helpers Daniel Vetter
2020-10-16  7:42   ` John Hubbard
2020-10-09  7:59 ` [PATCH v2 02/17] drm/exynos: Use FOLL_LONGTERM for g2d cmdlists Daniel Vetter
2020-10-09  7:59 ` [PATCH v2 03/17] misc/habana: Stop using frame_vector helpers Daniel Vetter
2020-10-10 20:26   ` Oded Gabbay
2020-10-10 21:32     ` Daniel Vetter
2020-10-10 21:41       ` Daniel Vetter
2020-10-10 21:47         ` Oded Gabbay
2020-10-16  7:45   ` John Hubbard
2020-10-09  7:59 ` [PATCH v2 04/17] misc/habana: Use FOLL_LONGTERM for userptr Daniel Vetter
2020-10-09  7:59 ` [PATCH v2 05/17] mm/frame-vector: Use FOLL_LONGTERM Daniel Vetter
2020-10-16  7:54   ` John Hubbard
2020-10-16  8:03     ` Daniel Vetter
2020-10-09  7:59 ` [PATCH v2 06/17] media: videobuf2: Move frame_vector into media subsystem Daniel Vetter
2020-10-09 10:14   ` Mauro Carvalho Chehab
2020-10-09 16:57     ` Daniel Vetter
2020-10-09  7:59 ` [PATCH v2 07/17] mm: Close race in generic_access_phys Daniel Vetter
2020-10-09  7:59 ` [PATCH v2 08/17] s390/pci: Remove races against pte updates Daniel Vetter
2020-10-12 14:03   ` Niklas Schnelle
2020-10-12 14:19     ` Daniel Vetter
2020-10-12 14:39       ` Niklas Schnelle
2020-10-21  7:55       ` Niklas Schnelle
2020-10-22  7:39         ` Daniel Vetter
2020-10-09  7:59 ` [PATCH v2 09/17] mm: Add unsafe_follow_pfn Daniel Vetter
2020-10-09 10:34   ` Mauro Carvalho Chehab
2020-10-09 12:21     ` Jason Gunthorpe
2020-10-09 12:37       ` Mauro Carvalho Chehab
2020-10-09 12:39         ` Mauro Carvalho Chehab [this message]
2020-10-09 12:48         ` Jason Gunthorpe
2020-10-09 17:52           ` Daniel Vetter
2020-10-09 18:01             ` Jason Gunthorpe
2020-10-09 19:31               ` Daniel Vetter
2020-10-10  9:21             ` Mauro Carvalho Chehab
2020-10-10 10:53               ` Daniel Vetter
2020-10-10 11:39                 ` Mauro Carvalho Chehab
2020-10-10 11:56                   ` Daniel Vetter
2020-10-10 17:22             ` Tomasz Figa
2020-10-10 21:35               ` Laurent Pinchart
2020-10-10 21:50                 ` Daniel Vetter
2020-10-11  6:27                   ` Mauro Carvalho Chehab
2020-10-11  6:36                     ` Mauro Carvalho Chehab
2020-10-10 21:11             ` Laurent Pinchart
2020-10-12 10:46           ` Marek Szyprowski
2020-10-12 13:49             ` Daniel Vetter
2020-10-10 17:30         ` Tomasz Figa
2020-10-09  7:59 ` [PATCH v2 10/17] media/videbuf1|2: Mark follow_pfn usage as unsafe Daniel Vetter
2020-10-10  9:24   ` Mauro Carvalho Chehab
2020-10-09  7:59 ` [PATCH v2 11/17] vfio/type1: Mark follow_pfn " Daniel Vetter
2020-10-09  7:59 ` [PATCH v2 12/17] PCI: Obey iomem restrictions for procfs mmap Daniel Vetter
2020-10-09  7:59 ` [PATCH v2 13/17] /dev/mem: Only set filp->f_mapping Daniel Vetter
2020-10-09  7:59 ` [PATCH v2 14/17] resource: Move devmem revoke code to resource framework Daniel Vetter
2020-10-09 10:59   ` Greg Kroah-Hartman
2020-10-09 12:31   ` Jason Gunthorpe
2020-10-09 14:24     ` Daniel Vetter
2020-10-09 14:32       ` Jason Gunthorpe
2020-10-09 18:28         ` Dan Williams
2020-10-15  0:09           ` Jason Gunthorpe
2020-10-15  7:52             ` Daniel Vetter
2020-10-15  7:55               ` Daniel Vetter
2020-10-15 15:29             ` Daniel Vetter
2020-10-09  7:59 ` [PATCH v2 15/17] sysfs: Support zapping of binary attr mmaps Daniel Vetter
2020-10-09 10:58   ` Greg Kroah-Hartman
2020-10-09  7:59 ` [PATCH v2 16/17] PCI: Revoke mappings like devmem Daniel Vetter
2020-10-09  7:59 ` [PATCH v2 17/17] drm/i915: Properly request PCI BARs Daniel Vetter
2020-10-09  9:47   ` Ville Syrjälä
2020-10-09 10:01     ` Daniel Vetter
2020-10-09 10:41       ` Ville Syrjälä
2020-10-09 14:18         ` Daniel Vetter

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