Hi Peter, David, On 07/01/2025 14:47, 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.
I just noticed that Andrew sent this to Linus and it's now in his tree; I'm suddenly very nervous that it doesn't have any acks. I don't suppose you would be able to do a quick review to calm the nerves?? Thanks, Ryan > > Co-developed-by: Mikołaj Lenczewski <miko.lenczew...@arm.com> > Signed-off-by: Mikołaj Lenczewski <miko.lenczew...@arm.com> > Signed-off-by: Ryan Roberts <ryan.robe...@arm.com> > Closes: > https://lore.kernel.org/linux-mm/810b44a8-d2ae-4107-b665-5a42eae2d...@arm.com/ > Fixes: 63b2d4174c4a ("userfaultfd: wp: add the writeprotect API to > userfaultfd ioctl") > Cc: sta...@vger.kernel.org > --- > include/linux/userfaultfd_k.h | 12 ++++++++++++ > mm/huge_memory.c | 12 ++++++++++++ > mm/hugetlb.c | 14 +++++++++++++- > mm/mremap.c | 32 +++++++++++++++++++++++++++++++- > 4 files changed, 68 insertions(+), 2 deletions(-) > > diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h > index cb40f1a1d081..75342022d144 100644 > --- a/include/linux/userfaultfd_k.h > +++ b/include/linux/userfaultfd_k.h > @@ -247,6 +247,13 @@ static inline bool vma_can_userfault(struct > vm_area_struct *vma, > vma_is_shmem(vma); > } > > +static inline bool vma_has_uffd_without_event_remap(struct vm_area_struct > *vma) > +{ > + struct userfaultfd_ctx *uffd_ctx = vma->vm_userfaultfd_ctx.ctx; > + > + return uffd_ctx && (uffd_ctx->features & UFFD_FEATURE_EVENT_REMAP) == 0; > +} > + > extern int dup_userfaultfd(struct vm_area_struct *, struct list_head *); > extern void dup_userfaultfd_complete(struct list_head *); > void dup_userfaultfd_fail(struct list_head *); > @@ -402,6 +409,11 @@ static inline bool userfaultfd_wp_async(struct > vm_area_struct *vma) > return false; > } > > +static inline bool vma_has_uffd_without_event_remap(struct vm_area_struct > *vma) > +{ > + return false; > +} > + > #endif /* CONFIG_USERFAULTFD */ > > static inline bool userfaultfd_wp_use_markers(struct vm_area_struct *vma) > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index c89aed1510f1..2654a9548749 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2212,6 +2212,16 @@ static pmd_t move_soft_dirty_pmd(pmd_t pmd) > return pmd; > } > > +static pmd_t clear_uffd_wp_pmd(pmd_t pmd) > +{ > + if (pmd_present(pmd)) > + pmd = pmd_clear_uffd_wp(pmd); > + else if (is_swap_pmd(pmd)) > + pmd = pmd_swp_clear_uffd_wp(pmd); > + > + return pmd; > +} > + > bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr, > unsigned long new_addr, pmd_t *old_pmd, pmd_t *new_pmd) > { > @@ -2250,6 +2260,8 @@ bool move_huge_pmd(struct vm_area_struct *vma, unsigned > long old_addr, > pgtable_trans_huge_deposit(mm, new_pmd, pgtable); > } > pmd = move_soft_dirty_pmd(pmd); > + if (vma_has_uffd_without_event_remap(vma)) > + pmd = clear_uffd_wp_pmd(pmd); > set_pmd_at(mm, new_addr, new_pmd, pmd); > if (force_flush) > flush_pmd_tlb_range(vma, old_addr, old_addr + PMD_SIZE); > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 354eec6f7e84..cdbc55d5384f 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5454,6 +5454,7 @@ static void move_huge_pte(struct vm_area_struct *vma, > unsigned long old_addr, > unsigned long new_addr, pte_t *src_pte, pte_t > *dst_pte, > unsigned long sz) > { > + bool need_clear_uffd_wp = vma_has_uffd_without_event_remap(vma); > struct hstate *h = hstate_vma(vma); > struct mm_struct *mm = vma->vm_mm; > spinlock_t *src_ptl, *dst_ptl; > @@ -5470,7 +5471,18 @@ static void move_huge_pte(struct vm_area_struct *vma, > unsigned long old_addr, > spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); > > pte = huge_ptep_get_and_clear(mm, old_addr, src_pte); > - set_huge_pte_at(mm, new_addr, dst_pte, pte, sz); > + > + if (need_clear_uffd_wp && pte_marker_uffd_wp(pte)) > + huge_pte_clear(mm, new_addr, dst_pte, sz); > + else { > + if (need_clear_uffd_wp) { > + if (pte_present(pte)) > + pte = huge_pte_clear_uffd_wp(pte); > + else if (is_swap_pte(pte)) > + pte = pte_swp_clear_uffd_wp(pte); > + } > + set_huge_pte_at(mm, new_addr, dst_pte, pte, sz); > + } > > if (src_ptl != dst_ptl) > spin_unlock(src_ptl); > diff --git a/mm/mremap.c b/mm/mremap.c > index 60473413836b..cff7f552f909 100644 > --- a/mm/mremap.c > +++ b/mm/mremap.c > @@ -138,6 +138,7 @@ static int move_ptes(struct vm_area_struct *vma, pmd_t > *old_pmd, > struct vm_area_struct *new_vma, pmd_t *new_pmd, > unsigned long new_addr, bool need_rmap_locks) > { > + bool need_clear_uffd_wp = vma_has_uffd_without_event_remap(vma); > struct mm_struct *mm = vma->vm_mm; > pte_t *old_pte, *new_pte, pte; > pmd_t dummy_pmdval; > @@ -216,7 +217,18 @@ static int move_ptes(struct vm_area_struct *vma, pmd_t > *old_pmd, > force_flush = true; > pte = move_pte(pte, old_addr, new_addr); > pte = move_soft_dirty_pte(pte); > - set_pte_at(mm, new_addr, new_pte, pte); > + > + if (need_clear_uffd_wp && pte_marker_uffd_wp(pte)) > + pte_clear(mm, new_addr, new_pte); > + else { > + if (need_clear_uffd_wp) { > + if (pte_present(pte)) > + pte = pte_clear_uffd_wp(pte); > + else if (is_swap_pte(pte)) > + pte = pte_swp_clear_uffd_wp(pte); > + } > + set_pte_at(mm, new_addr, new_pte, pte); > + } > } > > arch_leave_lazy_mmu_mode(); > @@ -278,6 +290,15 @@ static bool move_normal_pmd(struct vm_area_struct *vma, > unsigned long old_addr, > if (WARN_ON_ONCE(!pmd_none(*new_pmd))) > return false; > > + /* If this pmd belongs to a uffd vma with remap events disabled, we need > + * to ensure that the uffd-wp state is cleared from all pgtables. This > + * means recursing into lower page tables in move_page_tables(), and we > + * can reuse the existing code if we simply treat the entry as "not > + * moved". > + */ > + if (vma_has_uffd_without_event_remap(vma)) > + return false; > + > /* > * We don't have to worry about the ordering of src and dst > * ptlocks because exclusive mmap_lock prevents deadlock. > @@ -333,6 +354,15 @@ static bool move_normal_pud(struct vm_area_struct *vma, > unsigned long old_addr, > if (WARN_ON_ONCE(!pud_none(*new_pud))) > return false; > > + /* If this pud belongs to a uffd vma with remap events disabled, we need > + * to ensure that the uffd-wp state is cleared from all pgtables. This > + * means recursing into lower page tables in move_page_tables(), and we > + * can reuse the existing code if we simply treat the entry as "not > + * moved". > + */ > + if (vma_has_uffd_without_event_remap(vma)) > + return false; > + > /* > * We don't have to worry about the ordering of src and dst > * ptlocks because exclusive mmap_lock prevents deadlock.
