On 16.01.25 10:04, Ryan Roberts wrote:
On 15/01/2025 20:28, Peter Xu wrote:
On Tue, Jan 07, 2025 at 02:47:52PM +0000, Ryan Roberts wrote:
When mremap()ing a memory region previously registered with userfaultfd
as write-protected but without UFFD_FEATURE_EVENT_REMAP, an
inconsistency in flag clearing leads to a mismatch between the vma flags
(which have uffd-wp cleared) and the pte/pmd flags (which do not have
uffd-wp cleared). This mismatch causes a subsequent mprotect(PROT_WRITE)
to trigger a warning in page_table_check_pte_flags() due to setting the
pte to writable while uffd-wp is still set.
Fix this by always explicitly clearing the uffd-wp pte/pmd flags on any
such mremap() so that the values are consistent with the existing
clearing of VM_UFFD_WP. Be careful to clear the logical flag regardless
of its physical form; a PTE bit, a swap PTE bit, or a PTE marker. Cover
PTE, huge PMD and hugetlb paths.
Co-developed-by: Mikołaj Lenczewski <miko.lenczewski@xxxxxxx>
Signed-off-by: Mikołaj Lenczewski <miko.lenczewski@xxxxxxx>
Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
Closes: https://lore.kernel.org/linux-mm/810b44a8-d2ae-4107-b665-5a42eae2d948@xxxxxxx/
Fixes: 63b2d4174c4a ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl")
Cc: stable@xxxxxxxxxxxxxxx
Nothing I see wrong:
Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>
Great thanks!
Thanks Peter, for your feedback while I was out.
I remember that I skimmed over it without anything obvious jumping at
me, but decided to set it aside for later to take a closer look ....
which never happened.
Took another look, and it looks good to me! (we really must clear the
uffd-wp flags when losing the VMA flag)
--
Cheers,
David / dhildenb
