[CVE-2022-3523] mm/memory.c: fix race when faulting a device private page

[TrietHoang-DL]

Patch series "Fix several device private page reference counting issues", v2

commit 16ce101 upstream

This series aims to fix a number of page reference counting issues in drivers dealing with device private ZONE_DEVICE pages. These result in use-after-free type bugs, either from accessing a struct page which no longer exists because it has been removed or accessing fields within the struct page which are no longer valid because the page has been freed.

During normal usage it is unlikely these will cause any problems. However without these fixes it is possible to crash the kernel from userspace. These crashes can be triggered either by unloading the kernel module or unbinding the device from the driver prior to a userspace task exiting. In modules such as Nouveau it is also possible to trigger some of these issues by explicitly closing the device file-descriptor prior to the task exiting and then accessing device private memory.

This involves some minor changes to both PowerPC and AMD GPU code. Unfortunately I lack hardware to test either of those so any help there would be appreciated. The changes mimic what is done in for both Nouveau and hmm-tests though so I doubt they will cause problems.

This patch (of 8):

When the CPU tries to access a device private page the migrate_to_ram() callback associated with the pgmap for the page is called. However no reference is taken on the faulting page. Therefore a concurrent migration of the device private page can free the page and possibly the underlying pgmap. This results in a race which can crash the kernel due to the migrate_to_ram() function pointer becoming invalid. It also means drivers can't reliably read the zone_device_data field because the page may have been freed with memunmap_pages().

Close the race by getting a reference on the page while holding the ptl to ensure it has not been freed. Unfortunately the elevated reference count will cause the migration required to handle the fault to fail. To avoid this failure pass the faulting page into the migrate_vma functions so that if an elevated reference count is found it can be checked to see if it's expected or not.

[mpe@ellerman.id.au: fix build]
Link: https://lkml.kernel.org/r/87fsgbf3gh.fsf@mpe.ellerman.id.au
Link: https://lkml.kernel.org/r/cover.60659b549d8509ddecafad4f498ee7f03bb23c69.1664366292.git-series.apopple@nvidia.com
Link: https://lkml.kernel.org/r/d3e813178a59e565e8d78d9b9a4e2562f6494f90.1664366292.git-series.apopple@nvidia.com

Acked-by: Felix Kuehling Felix.Kuehling@amd.com
Cc: Jason Gunthorpe jgg@nvidia.com
Cc: John Hubbard jhubbard@nvidia.com
Cc: Ralph Campbell rcampbell@nvidia.com
Cc: Michael Ellerman mpe@ellerman.id.au
Cc: Lyude Paul lyude@redhat.com
Cc: Alex Deucher alexander.deucher@amd.com
Cc: Alex Sierra alex.sierra@amd.com
Cc: Ben Skeggs bskeggs@redhat.com
Cc: Christian König christian.koenig@amd.com
Cc: Dan Williams dan.j.williams@intel.com
Cc: David Hildenbrand david@redhat.com
Cc: "Huang, Ying" ying.huang@intel.com
Cc: Matthew Wilcox willy@infradead.org
Cc: Yang Shi shy828301@gmail.com
Cc: Zi Yan ziy@nvidia.com

The backport was adapted as follows:

• Kept mm/migrate_device.c deleted as in the target branch and applied the relevant fix to the corresponding code in mm/migrate.c.
• Convert migrate_folio_extra to migrate_page_extra