From: Jason Gunthorpe <jgg@ziepe.ca>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: "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,
"Dan Williams" <dan.j.williams@intel.com>,
"Kees Cook" <keescook@chromium.org>,
"Rik van Riel" <riel@redhat.com>,
"Benjamin Herrensmidt" <benh@kernel.crashing.org>,
"Dave Airlie" <airlied@linux.ie>,
"Hugh Dickins" <hugh@veritas.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"John Hubbard" <jhubbard@nvidia.com>,
"Jérôme Glisse" <jglisse@redhat.com>, "Jan Kara" <jack@suse.cz>,
"Daniel Vetter" <daniel.vetter@intel.com>
Subject: Re: [PATCH 07/13] mm: close race in generic_access_phys
Date: Wed, 7 Oct 2020 14:27:46 -0300 [thread overview]
Message-ID: <20201007172746.GU5177@ziepe.ca> (raw)
In-Reply-To: <20201007164426.1812530-8-daniel.vetter@ffwll.ch>
On Wed, Oct 07, 2020 at 06:44:20PM +0200, Daniel Vetter wrote:
> 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. Fix this.
>
> Since ioremap might need to manipulate pagetables too we need to drop
> the pt lock and have a retry loop if we raced.
>
> While at it, also add kerneldoc and improve the comment for the
> vma_ops->access function. It's for accessing, not for moving the
> memory from iomem to system memory, as the old comment seemed to
> suggest.
>
> References: 28b2ee20c7cb ("access_process_vm device memory infrastructure")
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Benjamin Herrensmidt <benh@kernel.crashing.org>
> Cc: Dave Airlie <airlied@linux.ie>
> Cc: Hugh Dickins <hugh@veritas.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Jérôme Glisse <jglisse@redhat.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: linux-mm@kvack.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-samsung-soc@vger.kernel.org
> Cc: linux-media@vger.kernel.org
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
> include/linux/mm.h | 3 ++-
> mm/memory.c | 44 ++++++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 44 insertions(+), 3 deletions(-)
This does seem to solve the race with revoke_devmem(), but it is really ugly.
It would be much nicer to wrap a rwsem around this access and the unmap.
Any place using it has a nice linear translation from vm_off to pfn,
so I don't think there is a such a good reason to use follow_pte in
the first place.
ie why not the helper be this:
int generic_access_phys(unsigned long pfn, unsigned long pgprot,
void *buf, size_t len, bool write)
Then something like dev/mem would compute pfn and obtain the lock:
dev_access(struct vm_area_struct *vma, unsigned long addr, void *buf, int len, int write)
{
cpu_addr = vma->vm_pgoff*PAGE_SIZE + (addr - vma->vm_start));
/* FIXME: Has to be over each page of len */
if (!devmem_is_allowed_access(PHYS_PFN(cpu_addr/4096)))
return -EPERM;
down_read(&mem_sem);
generic_access_phys(cpu_addr/4096, pgprot_val(vma->vm_page_prot),
buf, len, write);
up_read(&mem_sem);
}
The other cases looked simpler because they don't revoke, here the
mmap_sem alone should be enough protection, they would just need to
provide the linear translation to pfn.
What do you think?
Jason
next prev parent reply other threads:[~2020-10-07 17:27 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-07 16:44 [PATCH 00/13] follow_pfn and other iomap races Daniel Vetter
2020-10-07 16:44 ` [PATCH 01/13] drm/exynos: Stop using frame_vector helpers Daniel Vetter
2020-10-07 20:32 ` John Hubbard
2020-10-07 21:32 ` Daniel Vetter
2020-10-07 21:36 ` John Hubbard
2020-10-07 21:50 ` Daniel Vetter
2020-10-07 16:44 ` [PATCH 02/13] drm/exynos: Use FOLL_LONGTERM for g2d cmdlists Daniel Vetter
2020-10-07 20:43 ` John Hubbard
2020-10-07 16:44 ` [PATCH 03/13] misc/habana: Stop using frame_vector helpers Daniel Vetter
2020-10-07 20:38 ` John Hubbard
2020-10-07 16:44 ` [PATCH 04/13] misc/habana: Use FOLL_LONGTERM for userptr Daniel Vetter
2020-10-07 20:46 ` John Hubbard
2020-10-07 16:44 ` [PATCH 05/13] mm/frame-vector: Use FOLL_LONGTERM Daniel Vetter
2020-10-07 16:53 ` Jason Gunthorpe
2020-10-07 17:12 ` Daniel Vetter
2020-10-07 17:33 ` Jason Gunthorpe
2020-10-07 21:13 ` John Hubbard
2020-10-07 21:30 ` Daniel Vetter
2020-10-07 16:44 ` [PATCH 06/13] media: videobuf2: Move frame_vector into media subsystem Daniel Vetter
2020-10-07 22:18 ` John Hubbard
2020-10-07 16:44 ` [PATCH 07/13] mm: close race in generic_access_phys Daniel Vetter
2020-10-07 17:27 ` Jason Gunthorpe [this message]
2020-10-07 18:01 ` Daniel Vetter
2020-10-07 23:21 ` Jason Gunthorpe
2020-10-08 0:44 ` John Hubbard
2020-10-08 7:23 ` Daniel Vetter
2020-10-07 16:44 ` [PATCH 08/13] s390/pci: Remove races against pte updates Daniel Vetter
2020-10-08 16:44 ` Gerald Schaefer
2020-10-08 17:16 ` Daniel Vetter
2020-10-07 16:44 ` [PATCH 09/13] PCI: obey iomem restrictions for procfs mmap Daniel Vetter
2020-10-07 18:46 ` Bjorn Helgaas
2020-10-07 16:44 ` [PATCH 10/13] PCI: revoke mappings like devmem Daniel Vetter
2020-10-07 18:41 ` Bjorn Helgaas
2020-10-07 19:24 ` Daniel Vetter
2020-10-07 19:33 ` Dan Williams
2020-10-07 19:47 ` Daniel Vetter
2020-10-07 22:23 ` Dan Williams
2020-10-07 22:29 ` Dan Williams
2020-10-08 8:09 ` Daniel Vetter
2020-10-07 23:24 ` Jason Gunthorpe
2020-10-08 7:31 ` Daniel Vetter
2020-10-08 7:49 ` Dan Williams
2020-10-08 8:13 ` Daniel Vetter
2020-10-08 8:35 ` Dan Williams
2020-10-08 12:41 ` Jason Gunthorpe
2020-10-07 16:44 ` [PATCH 11/13] mm: add unsafe_follow_pfn Daniel Vetter
2020-10-07 17:36 ` Jason Gunthorpe
2020-10-07 18:10 ` Daniel Vetter
2020-10-07 19:00 ` Jason Gunthorpe
2020-10-07 19:38 ` Daniel Vetter
2020-10-07 16:44 ` [PATCH 12/13] media/videbuf1|2: Mark follow_pfn usage as unsafe Daniel Vetter
2020-10-07 16:44 ` [PATCH 13/13] vfio/type1: Mark follow_pfn " Daniel Vetter
2020-10-07 17:39 ` Jason Gunthorpe
2020-10-07 18:14 ` Daniel Vetter
2020-10-07 18:47 ` Jason Gunthorpe
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