mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2026-09-22 09:34:56 +02:00
Kiryl Shutsemau
60d696a037
[ Upstream commit8e80af52db] userfaultfd_must_wait() and userfaultfd_huge_must_wait() read the PTE without taking the page table lock and then apply pte_write() / huge_pte_write() to it. Those accessors decode bits from the present encoding only; on a swap or migration entry they read the offset bits that happen to share the same position and return an undefined result. The intent of the check is "is this fault still WP-blocked?". A non-marker swap entry means the page is in transit -- the userfault context the original fault delivered against is no longer the same, and the swap-in or migration completion path will re-deliver a fresh fault if userspace still needs to handle it. Worst case under the current code the garbage write bit says "wait", and the thread stays asleep until a UFFDIO_WAKE that may never arrive. Gate the writability check on pte_present() so the lockless re-check only inspects present-PTE bits when the entry is actually present. The non-present, non-marker case returns "don't wait" and lets the fault path retry. Link: https://lore.kernel.org/20260529172331.356655-6-kas@kernel.org Fixes:369cd2121b("userfaultfd: hugetlbfs: userfaultfd_huge_must_wait for hugepmd ranges") Fixes:63b2d4174c("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl") Signed-off-by: Kiryl Shutsemau <kas@kernel.org> Reported-by: Sashiko AI review <sashiko-bot@kernel.org> Reviewed-by: Lorenzo Stoakes <ljs@kernel.org> Cc: David Hildenbrand <david@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport <rppt@kernel.org> Cc: Peter Xu <peterx@redhat.com> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Vlastimil Babka <vbabka@kernel.org> Cc: Balbir Singh <balbirs@nvidia.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> [ kas: apply to fs/userfaultfd.c and fold the pte_present()/ huge_pte_present() gate into the existing writability checks; this tree predates the marker/return-style refactor of these functions ] Signed-off-by: Kiryl Shutsemau <kas@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.