From bd56086f10186e2c205429cc12b16e43aacb1c7e Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Fri, 15 Jan 2016 16:55:46 -0800 Subject: [PATCH] thp: fix split_huge_page() after mremap() of THP Sasha Levin has reported KASAN out-of-bounds bug[1]. It points to "if (!is_swap_pte(pte[i]))" in unfreeze_page_vma() as a problematic access. The cause is that split_huge_page() doesn't handle THP correctly if it's not allingned to PMD boundary. It can happen after mremap(). Test-case (not always triggers the bug): #define _GNU_SOURCE #include #include #include #define MB (1024UL*1024) #define SIZE (2*MB) #define BASE ((void *)0x400000000000) int main() { char *p; p = mmap(BASE, SIZE, PROT_READ | PROT_WRITE, MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0); if (p == MAP_FAILED) perror("mmap"), exit(1); p = mremap(BASE, SIZE, SIZE, MREMAP_FIXED | MREMAP_MAYMOVE, BASE + SIZE + 8192); if (p == MAP_FAILED) perror("mremap"), exit(1); system("echo 1 > /sys/kernel/debug/split_huge_pages"); return 0; } The patch fixes freeze and unfreeze paths to handle page table boundary crossing. It also makes mapcount vs count check in split_huge_page_to_list() stricter: - after freeze we don't expect any subpage mapped as we remove them from rmap when setting up migration entries; - count must be 1, meaning only caller has reference to the page; [1] https://gist.github.com/sashalevin/c67fbea55e7c0576972a Signed-off-by: Kirill A. Shutemov Reported-by: Sasha Levin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/huge_memory.c | 70 +++++++++++++++++++++++++++++++++--------------- 1 file changed, 49 insertions(+), 21 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 1a4989fef08f..9d12d63a0ddd 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2990,6 +2990,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma, static void freeze_page_vma(struct vm_area_struct *vma, struct page *page, unsigned long address) { + unsigned long haddr = address & HPAGE_PMD_MASK; spinlock_t *ptl; pgd_t *pgd; pud_t *pud; @@ -3019,34 +3020,47 @@ static void freeze_page_vma(struct vm_area_struct *vma, struct page *page, } if (pmd_trans_huge(*pmd)) { if (page == pmd_page(*pmd)) - __split_huge_pmd_locked(vma, pmd, address, true); + __split_huge_pmd_locked(vma, pmd, haddr, true); spin_unlock(ptl); return; } spin_unlock(ptl); pte = pte_offset_map_lock(vma->vm_mm, pmd, address, &ptl); - for (i = 0; i < nr; i++, address += PAGE_SIZE, page++) { + for (i = 0; i < nr; i++, address += PAGE_SIZE, page++, pte++) { pte_t entry, swp_pte; swp_entry_t swp_entry; - if (!pte_present(pte[i])) + /* + * We've just crossed page table boundary: need to map next one. + * It can happen if THP was mremaped to non PMD-aligned address. + */ + if (unlikely(address == haddr + HPAGE_PMD_SIZE)) { + pte_unmap_unlock(pte - 1, ptl); + pmd = mm_find_pmd(vma->vm_mm, address); + if (!pmd) + return; + pte = pte_offset_map_lock(vma->vm_mm, pmd, + address, &ptl); + } + + if (!pte_present(*pte)) continue; - if (page_to_pfn(page) != pte_pfn(pte[i])) + if (page_to_pfn(page) != pte_pfn(*pte)) continue; flush_cache_page(vma, address, page_to_pfn(page)); - entry = ptep_clear_flush(vma, address, pte + i); + entry = ptep_clear_flush(vma, address, pte); if (pte_dirty(entry)) SetPageDirty(page); swp_entry = make_migration_entry(page, pte_write(entry)); swp_pte = swp_entry_to_pte(swp_entry); if (pte_soft_dirty(entry)) swp_pte = pte_swp_mksoft_dirty(swp_pte); - set_pte_at(vma->vm_mm, address, pte + i, swp_pte); + set_pte_at(vma->vm_mm, address, pte, swp_pte); page_remove_rmap(page, false); put_page(page); } - pte_unmap_unlock(pte, ptl); + pte_unmap_unlock(pte - 1, ptl); } static void freeze_page(struct anon_vma *anon_vma, struct page *page) @@ -3058,14 +3072,13 @@ static void freeze_page(struct anon_vma *anon_vma, struct page *page) anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff + HPAGE_PMD_NR - 1) { - unsigned long haddr; + unsigned long address = __vma_address(page, avc->vma); - haddr = __vma_address(page, avc->vma) & HPAGE_PMD_MASK; mmu_notifier_invalidate_range_start(avc->vma->vm_mm, - haddr, haddr + HPAGE_PMD_SIZE); - freeze_page_vma(avc->vma, page, haddr); + address, address + HPAGE_PMD_SIZE); + freeze_page_vma(avc->vma, page, address); mmu_notifier_invalidate_range_end(avc->vma->vm_mm, - haddr, haddr + HPAGE_PMD_SIZE); + address, address + HPAGE_PMD_SIZE); } } @@ -3076,6 +3089,7 @@ static void unfreeze_page_vma(struct vm_area_struct *vma, struct page *page, pmd_t *pmd; pte_t *pte, entry; swp_entry_t swp_entry; + unsigned long haddr = address & HPAGE_PMD_MASK; int i, nr = HPAGE_PMD_NR; /* Skip pages which doesn't belong to the VMA */ @@ -3089,12 +3103,26 @@ static void unfreeze_page_vma(struct vm_area_struct *vma, struct page *page, pmd = mm_find_pmd(vma->vm_mm, address); if (!pmd) return; + pte = pte_offset_map_lock(vma->vm_mm, pmd, address, &ptl); - for (i = 0; i < nr; i++, address += PAGE_SIZE, page++) { - if (!is_swap_pte(pte[i])) + for (i = 0; i < nr; i++, address += PAGE_SIZE, page++, pte++) { + /* + * We've just crossed page table boundary: need to map next one. + * It can happen if THP was mremaped to non-PMD aligned address. + */ + if (unlikely(address == haddr + HPAGE_PMD_SIZE)) { + pte_unmap_unlock(pte - 1, ptl); + pmd = mm_find_pmd(vma->vm_mm, address); + if (!pmd) + return; + pte = pte_offset_map_lock(vma->vm_mm, pmd, + address, &ptl); + } + + if (!is_swap_pte(*pte)) continue; - swp_entry = pte_to_swp_entry(pte[i]); + swp_entry = pte_to_swp_entry(*pte); if (!is_migration_entry(swp_entry)) continue; if (migration_entry_to_page(swp_entry) != page) @@ -3110,12 +3138,12 @@ static void unfreeze_page_vma(struct vm_area_struct *vma, struct page *page, entry = maybe_mkwrite(entry, vma); flush_dcache_page(page); - set_pte_at(vma->vm_mm, address, pte + i, entry); + set_pte_at(vma->vm_mm, address, pte, entry); /* No need to invalidate - it was non-present before */ - update_mmu_cache(vma, address, pte + i); + update_mmu_cache(vma, address, pte); } - pte_unmap_unlock(pte, ptl); + pte_unmap_unlock(pte - 1, ptl); } static void unfreeze_page(struct anon_vma *anon_vma, struct page *page) @@ -3321,7 +3349,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) spin_lock(&split_queue_lock); count = page_count(head); mapcount = total_mapcount(head); - if (mapcount == count - 1) { + if (!mapcount && count == 1) { if (!list_empty(page_deferred_list(head))) { split_queue_len--; list_del(page_deferred_list(head)); @@ -3329,13 +3357,13 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) spin_unlock(&split_queue_lock); __split_huge_page(page, list); ret = 0; - } else if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount > count - 1) { + } else if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) { spin_unlock(&split_queue_lock); pr_alert("total_mapcount: %u, page_count(): %u\n", mapcount, count); if (PageTail(page)) dump_page(head, NULL); - dump_page(page, "total_mapcount(head) > page_count(head) - 1"); + dump_page(page, "total_mapcount(head) > 0"); BUG(); } else { spin_unlock(&split_queue_lock); -- 2.20.1