From: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> Subject: mm: change page type prior to adding page table entry Patch series "page table check", v3. Ensure that some memory corruptions are prevented by checking at the time of insertion of entries into user page tables that there is no illegal sharing. We have recently found a problem [1] that existed in kernel since 4.14. The problem was caused by broken page ref count and led to memory leaking from one process into another. The problem was accidentally detected by studying a dump of one process and noticing that one page contains memory that should not belong to this process. There are some other page->_refcount related problems that were recently fixed: [2], [3] which potentially could also lead to illegal sharing. In addition to hardening refcount [4] itself, this work is an attempt to prevent this class of memory corruption issues. It uses a simple state machine that is independent from regular MM logic to check for illegal sharing at time pages are inserted and removed from page tables. [1] https://lore.kernel.org/all/xr9335nxwc5y.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxx [2] https://lore.kernel.org/all/1582661774-30925-2-git-send-email-akaher@xxxxxxxxxx [3] https://lore.kernel.org/all/20210622021423.154662-3-mike.kravetz@xxxxxxxxxx [4] https://lore.kernel.org/all/20211221150140.988298-1-pasha.tatashin@xxxxxxxxxx This patch (of 4): There are a few places where we first update the entry in the user page table, and later change the struct page to indicate that this is anonymous or file page. In most places, however, we first configure the page metadata and then insert entries into the page table. Page table check, will use the information from struct page to verify the type of entry is inserted. Change the order in all places to first update struct page, and later to update page table. This means that we first do calls that may change the type of page (anon or file): page_move_anon_rmap page_add_anon_rmap do_page_add_anon_rmap page_add_new_anon_rmap page_add_file_rmap hugepage_add_anon_rmap hugepage_add_new_anon_rmap And after that do calls that add entries to the page table: set_huge_pte_at set_pte_at Link: https://lkml.kernel.org/r/20211221154650.1047963-1-pasha.tatashin@xxxxxxxxxx Link: https://lkml.kernel.org/r/20211221154650.1047963-2-pasha.tatashin@xxxxxxxxxx Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Paul Turner <pjt@xxxxxxxxxx> Cc: Wei Xu <weixugc@xxxxxxxxxx> Cc: Greg Thelen <gthelen@xxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx> Cc: Sami Tolvanen <samitolvanen@xxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: Frederic Weisbecker <frederic@xxxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> Cc: Jiri Slaby <jirislaby@xxxxxxxxxx> Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/hugetlb.c | 6 +++--- mm/memory.c | 9 +++++---- mm/migrate.c | 5 ++--- mm/swapfile.c | 4 ++-- 4 files changed, 12 insertions(+), 12 deletions(-) --- a/mm/hugetlb.c~mm-change-page-type-prior-to-adding-page-table-entry +++ a/mm/hugetlb.c @@ -4684,8 +4684,8 @@ hugetlb_install_page(struct vm_area_stru struct page *new_page) { __SetPageUptodate(new_page); - set_huge_pte_at(vma->vm_mm, addr, ptep, make_huge_pte(vma, new_page, 1)); hugepage_add_new_anon_rmap(new_page, vma, addr); + set_huge_pte_at(vma->vm_mm, addr, ptep, make_huge_pte(vma, new_page, 1)); hugetlb_count_add(pages_per_huge_page(hstate_vma(vma)), vma->vm_mm); ClearHPageRestoreReserve(new_page); SetHPageMigratable(new_page); @@ -5259,10 +5259,10 @@ retry_avoidcopy: /* Break COW */ huge_ptep_clear_flush(vma, haddr, ptep); mmu_notifier_invalidate_range(mm, range.start, range.end); - set_huge_pte_at(mm, haddr, ptep, - make_huge_pte(vma, new_page, 1)); page_remove_rmap(old_page, true); hugepage_add_new_anon_rmap(new_page, vma, haddr); + set_huge_pte_at(mm, haddr, ptep, + make_huge_pte(vma, new_page, 1)); SetHPageMigratable(new_page); /* Make the old page be freed below */ new_page = old_page; --- a/mm/memory.c~mm-change-page-type-prior-to-adding-page-table-entry +++ a/mm/memory.c @@ -720,8 +720,6 @@ static void restore_exclusive_pte(struct else if (is_writable_device_exclusive_entry(entry)) pte = maybe_mkwrite(pte_mkdirty(pte), vma); - set_pte_at(vma->vm_mm, address, ptep, pte); - /* * No need to take a page reference as one was already * created when the swap entry was made. @@ -735,6 +733,8 @@ static void restore_exclusive_pte(struct */ WARN_ON_ONCE(!PageAnon(page)); + set_pte_at(vma->vm_mm, address, ptep, pte); + if (vma->vm_flags & VM_LOCKED) mlock_vma_page(page); @@ -3640,8 +3640,6 @@ vm_fault_t do_swap_page(struct vm_fault pte = pte_mkuffd_wp(pte); pte = pte_wrprotect(pte); } - set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte); - arch_do_swap_page(vma->vm_mm, vma, vmf->address, pte, vmf->orig_pte); vmf->orig_pte = pte; /* ksm created a completely new copy */ @@ -3652,6 +3650,9 @@ vm_fault_t do_swap_page(struct vm_fault do_page_add_anon_rmap(page, vma, vmf->address, exclusive); } + set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte); + arch_do_swap_page(vma->vm_mm, vma, vmf->address, pte, vmf->orig_pte); + swap_free(entry); if (mem_cgroup_swap_full(page) || (vma->vm_flags & VM_LOCKED) || PageMlocked(page)) --- a/mm/migrate.c~mm-change-page-type-prior-to-adding-page-table-entry +++ a/mm/migrate.c @@ -236,20 +236,19 @@ static bool remove_migration_pte(struct pte = pte_mkhuge(pte); pte = arch_make_huge_pte(pte, shift, vma->vm_flags); - set_huge_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte); if (PageAnon(new)) hugepage_add_anon_rmap(new, vma, pvmw.address); else page_dup_rmap(new, true); + set_huge_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte); } else #endif { - set_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte); - if (PageAnon(new)) page_add_anon_rmap(new, vma, pvmw.address, false); else page_add_file_rmap(new, false); + set_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte); } if (vma->vm_flags & VM_LOCKED && !PageTransCompound(new)) mlock_vma_page(new); --- a/mm/swapfile.c~mm-change-page-type-prior-to-adding-page-table-entry +++ a/mm/swapfile.c @@ -1917,14 +1917,14 @@ static int unuse_pte(struct vm_area_stru dec_mm_counter(vma->vm_mm, MM_SWAPENTS); inc_mm_counter(vma->vm_mm, MM_ANONPAGES); get_page(page); - set_pte_at(vma->vm_mm, addr, pte, - pte_mkold(mk_pte(page, vma->vm_page_prot))); if (page == swapcache) { page_add_anon_rmap(page, vma, addr, false); } else { /* ksm created a completely new copy */ page_add_new_anon_rmap(page, vma, addr, false); lru_cache_add_inactive_or_unevictable(page, vma); } + set_pte_at(vma->vm_mm, addr, pte, + pte_mkold(mk_pte(page, vma->vm_page_prot))); swap_free(entry); out: pte_unmap_unlock(pte, ptl); _
