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Lance Yang
bb1c19636a
[ Upstream commit6f86d0534f] When a page fault occurs in a secret memory file created with `memfd_secret(2)`, the kernel will allocate a new page for it, mark the underlying page as not-present in the direct map, and add it to the file mapping. If two tasks cause a fault in the same page concurrently, both could end up allocating a page and removing the page from the direct map, but only one would succeed in adding the page to the file mapping. The task that failed undoes the effects of its attempt by (a) freeing the page again and (b) putting the page back into the direct map. However, by doing these two operations in this order, the page becomes available to the allocator again before it is placed back in the direct mapping. If another task attempts to allocate the page between (a) and (b), and the kernel tries to access it via the direct map, it would result in a supervisor not-present page fault. Fix the ordering to restore the direct map before the page is freed. Link: https://lkml.kernel.org/r/20251031120955.92116-1-lance.yang@linux.dev Fixes:1507f51255("mm: introduce memfd_secret system call to create "secret" memory areas") Signed-off-by: Lance Yang <lance.yang@linux.dev> Reported-by: Google Big Sleep <big-sleep-vuln-reports@google.com> Closes: https://lore.kernel.org/linux-mm/CAEXGt5QeDpiHTu3K9tvjUTPqo+d-=wuCNYPa+6sWKrdQJ-ATdg@mail.gmail.com/ Acked-by: David Hildenbrand <david@redhat.com> Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> (cherry picked from commit6f86d0534f) [rppt: replaced folio with page in the patch and in the changelog] Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>