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@arm.com Signed-off-by: Mikołaj Lenczewski miko.lenczewski@arm.com Signed-off-by: Ryan Roberts ryan.roberts@arm.com Closes: https://lore.kernel.org/linux-mm/810b44a8-d2ae-4107-b665-5a42eae2d948@arm.co... Fixes: 63b2d4174c4a ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl") Cc: stable@vger.kernel.org
Nothing I see wrong:
Reviewed-by: Peter Xu peterx@redhat.com
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)