From: Qi Zheng Date: Wed, 4 Dec 2024 11:09:42 +0000 (+0800) Subject: mm: userfaultfd: recheck dst_pmd entry in move_pages_pte() X-Git-Tag: v6.14-rc1~77^2~251 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=dd95d2782a251637f60c068ac7aeb3eebf57ae3b;p=thirdparty%2Flinux.git mm: userfaultfd: recheck dst_pmd entry in move_pages_pte() In move_pages_pte(), since dst_pte needs to be none, the subsequent pte_same() check cannot prevent the dst_pte page from being freed concurrently, so we also need to abtain dst_pmdval and recheck pmd_same(). Otherwise, once we support empty PTE page reclaimation for anonymous pages, it may result in moving the src_pte page into the dts_pte page that is about to be freed by RCU. [zhengqi.arch@bytedance.com: remove WARN_ON_ONCE()s] Link: https://lkml.kernel.org/r/20241210084156.89877-1-zhengqi.arch@bytedance.com Link: https://lkml.kernel.org/r/8108c262757fc492626f3a2ffc44b775f2710e16.1733305182.git.zhengqi.arch@bytedance.com Signed-off-by: Qi Zheng Cc: Andy Lutomirski Cc: Catalin Marinas Cc: Dave Hansen Cc: David Hildenbrand Cc: David Rientjes Cc: Hugh Dickins Cc: Jann Horn Cc: Lorenzo Stoakes Cc: Matthew Wilcox Cc: Mel Gorman Cc: Muchun Song Cc: Peter Xu Cc: Peter Zijlstra Cc: Will Deacon Cc: Zach O'Keefe Cc: Dan Carpenter Signed-off-by: Andrew Morton --- diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 60a0be33766ff..af3dfc3633dbe 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -1020,6 +1020,14 @@ void double_pt_unlock(spinlock_t *ptl1, __release(ptl2); } +static inline bool is_pte_pages_stable(pte_t *dst_pte, pte_t *src_pte, + pte_t orig_dst_pte, pte_t orig_src_pte, + pmd_t *dst_pmd, pmd_t dst_pmdval) +{ + return pte_same(ptep_get(src_pte), orig_src_pte) && + pte_same(ptep_get(dst_pte), orig_dst_pte) && + pmd_same(dst_pmdval, pmdp_get_lockless(dst_pmd)); +} static int move_present_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, @@ -1027,6 +1035,7 @@ static int move_present_pte(struct mm_struct *mm, unsigned long dst_addr, unsigned long src_addr, pte_t *dst_pte, pte_t *src_pte, pte_t orig_dst_pte, pte_t orig_src_pte, + pmd_t *dst_pmd, pmd_t dst_pmdval, spinlock_t *dst_ptl, spinlock_t *src_ptl, struct folio *src_folio) { @@ -1034,8 +1043,8 @@ static int move_present_pte(struct mm_struct *mm, double_pt_lock(dst_ptl, src_ptl); - if (!pte_same(ptep_get(src_pte), orig_src_pte) || - !pte_same(ptep_get(dst_pte), orig_dst_pte)) { + if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte, + dst_pmd, dst_pmdval)) { err = -EAGAIN; goto out; } @@ -1071,6 +1080,7 @@ static int move_swap_pte(struct mm_struct *mm, unsigned long dst_addr, unsigned long src_addr, pte_t *dst_pte, pte_t *src_pte, pte_t orig_dst_pte, pte_t orig_src_pte, + pmd_t *dst_pmd, pmd_t dst_pmdval, spinlock_t *dst_ptl, spinlock_t *src_ptl) { if (!pte_swp_exclusive(orig_src_pte)) @@ -1078,8 +1088,8 @@ static int move_swap_pte(struct mm_struct *mm, double_pt_lock(dst_ptl, src_ptl); - if (!pte_same(ptep_get(src_pte), orig_src_pte) || - !pte_same(ptep_get(dst_pte), orig_dst_pte)) { + if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte, + dst_pmd, dst_pmdval)) { double_pt_unlock(dst_ptl, src_ptl); return -EAGAIN; } @@ -1097,13 +1107,14 @@ static int move_zeropage_pte(struct mm_struct *mm, unsigned long dst_addr, unsigned long src_addr, pte_t *dst_pte, pte_t *src_pte, pte_t orig_dst_pte, pte_t orig_src_pte, + pmd_t *dst_pmd, pmd_t dst_pmdval, spinlock_t *dst_ptl, spinlock_t *src_ptl) { pte_t zero_pte; double_pt_lock(dst_ptl, src_ptl); - if (!pte_same(ptep_get(src_pte), orig_src_pte) || - !pte_same(ptep_get(dst_pte), orig_dst_pte)) { + if (!is_pte_pages_stable(dst_pte, src_pte, orig_dst_pte, orig_src_pte, + dst_pmd, dst_pmdval)) { double_pt_unlock(dst_ptl, src_ptl); return -EAGAIN; } @@ -1136,6 +1147,7 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pte_t *src_pte = NULL; pte_t *dst_pte = NULL; pmd_t dummy_pmdval; + pmd_t dst_pmdval; struct folio *src_folio = NULL; struct anon_vma *src_anon_vma = NULL; struct mmu_notifier_range range; @@ -1148,11 +1160,11 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, retry: /* * Use the maywrite version to indicate that dst_pte will be modified, - * but since we will use pte_same() to detect the change of the pte - * entry, there is no need to get pmdval, so just pass a dummy variable - * to it. + * since dst_pte needs to be none, the subsequent pte_same() check + * cannot prevent the dst_pte page from being freed concurrently, so we + * also need to abtain dst_pmdval and recheck pmd_same() later. */ - dst_pte = pte_offset_map_rw_nolock(mm, dst_pmd, dst_addr, &dummy_pmdval, + dst_pte = pte_offset_map_rw_nolock(mm, dst_pmd, dst_addr, &dst_pmdval, &dst_ptl); /* Retry if a huge pmd materialized from under us */ @@ -1161,7 +1173,11 @@ retry: goto out; } - /* same as dst_pte */ + /* + * Unlike dst_pte, the subsequent pte_same() check can ensure the + * stability of the src_pte page, so there is no need to get pmdval, + * just pass a dummy variable to it. + */ src_pte = pte_offset_map_rw_nolock(mm, src_pmd, src_addr, &dummy_pmdval, &src_ptl); @@ -1177,8 +1193,8 @@ retry: } /* Sanity checks before the operation */ - if (WARN_ON_ONCE(pmd_none(*dst_pmd)) || WARN_ON_ONCE(pmd_none(*src_pmd)) || - WARN_ON_ONCE(pmd_trans_huge(*dst_pmd)) || WARN_ON_ONCE(pmd_trans_huge(*src_pmd))) { + if (pmd_none(*dst_pmd) || pmd_none(*src_pmd) || + pmd_trans_huge(*dst_pmd) || pmd_trans_huge(*src_pmd)) { err = -EINVAL; goto out; } @@ -1213,7 +1229,7 @@ retry: err = move_zeropage_pte(mm, dst_vma, src_vma, dst_addr, src_addr, dst_pte, src_pte, orig_dst_pte, orig_src_pte, - dst_ptl, src_ptl); + dst_pmd, dst_pmdval, dst_ptl, src_ptl); goto out; } @@ -1303,8 +1319,8 @@ retry: err = move_present_pte(mm, dst_vma, src_vma, dst_addr, src_addr, dst_pte, src_pte, - orig_dst_pte, orig_src_pte, - dst_ptl, src_ptl, src_folio); + orig_dst_pte, orig_src_pte, dst_pmd, + dst_pmdval, dst_ptl, src_ptl, src_folio); } else { entry = pte_to_swp_entry(orig_src_pte); if (non_swap_entry(entry)) { @@ -1319,10 +1335,9 @@ retry: goto out; } - err = move_swap_pte(mm, dst_addr, src_addr, - dst_pte, src_pte, - orig_dst_pte, orig_src_pte, - dst_ptl, src_ptl); + err = move_swap_pte(mm, dst_addr, src_addr, dst_pte, src_pte, + orig_dst_pte, orig_src_pte, dst_pmd, + dst_pmdval, dst_ptl, src_ptl); } out: