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> One trivial thing: some multiple-line comments is following the net/ coding style rather than mm/, but well.. I don't think it's a huge deal. https://www.kernel.org/doc/html/v4.10/process/coding-style.html#commenting Thanks again. -- Peter Xu
