numa_rebuild_large_mapping() and do_swap_page() can be tricked into generating an address wraparound, crashing the kernel. All that's required is to map a tail page of a large folio close enough to the start/end of the address space to e.g., make unsigned long addr_start = addr - (nr << PAGE_SHIFT); to wrap around. Let's fix it by providing a better helper, folio_scan_range(), that takes care of staying within VMA and page table boundaries while handling possible wraparounds. There are some nasty details, like not being able to use pmd_addr_end() in this context. Add some helpful comments for these cases. Reported-by: Kyle Zeng Fixes: d2136d749d76 ("mm: support multi-size THP numa balancing") Fixes: 508758960b8d ("mm: swap: entirely map large folios found in swapcache") Cc: stable@vger.kernel.org Reviewed-by: Lorenzo Stoakes (ARM) Reviewed-by: Kiryl Shutsemau (Meta) Reviewed-by: Baolin Wang Reviewed-by: Lance Yang Signed-off-by: David Hildenbrand (Arm) --- Changes in v2: - s/folio_scan_pte_range/folio_pte_range/ - Add more comments + improve existing ones. - Link to v1: https://patch.msgid.link/20261013-folio_pte_scan_range-v1-1-c50dc30bf6ad@kernel.org --- mm/memory.c | 50 ++++++++++++++++++++++++++++++++++++-------------- 1 file changed, 36 insertions(+), 14 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 1f5d5f7d39cd2..fa29d7a8d0c20 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4933,6 +4933,34 @@ static void check_swap_exclusive(struct folio *folio, swp_entry_t entry, } while (--nr_pages); } +/* + * Get the address range in which a folio might be mapped, assuming its pages + * are mapped consecutively and the folio page at the given idx is mapped at + * the given address. + */ +static void folio_pte_range(const struct folio *folio, + const struct vm_area_struct *vma, unsigned long addr, + unsigned long idx, unsigned long *start, unsigned long *end) +{ + /* Stay within the page table and VMA boundaries. */ + const unsigned long pmd_start = addr & PMD_MASK; + const unsigned long pmd_end = pmd_start + PMD_SIZE; + const unsigned long lower = max(pmd_start, vma->vm_start); + /* + * We cannot use pmd_addr_end(), as it does not clamp reliably. To + * avoid wraparounds, compute using the inclusive end. + */ + const unsigned long upper = min(pmd_end - 1, vma->vm_end - 1) + 1; + const unsigned long offset = idx << PAGE_SHIFT; + + /* + * Avoid start/end addresses wrapping by not adding/subtracting more + * than the lower/upper limits would allow. + */ + *start = addr - min(addr - lower, offset); + *end = addr + min(upper - addr, folio_size(folio) - offset); +} + /* * We enter with either the VMA lock or the mmap_lock held (see * FAULT_FLAG_VMA_LOCK), and pte mapped but not yet locked. @@ -5121,16 +5149,15 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) address = vmf->address; ptep = vmf->pte; if (folio_test_large(folio) && folio_test_swapcache(folio)) { - int nr = folio_nr_pages(folio); - unsigned long idx = folio_page_idx(folio, page); - unsigned long folio_start = address - idx * PAGE_SIZE; - unsigned long folio_end = folio_start + nr * PAGE_SIZE; + const int nr = folio_nr_pages(folio); + const unsigned long idx = folio_page_idx(folio, page); + unsigned long folio_start, folio_end; pte_t *folio_ptep; pte_t folio_pte; - if (unlikely(folio_start < max(address & PMD_MASK, vma->vm_start))) - goto check_folio; - if (unlikely(folio_end > pmd_addr_end(address, vma->vm_end))) + folio_pte_range(folio, vma, address, idx, &folio_start, + &folio_end); + if (unlikely((folio_end - folio_start) >> PAGE_SHIFT != nr)) goto check_folio; folio_ptep = vmf->pte - idx; @@ -6280,16 +6307,11 @@ static void numa_rebuild_large_mapping(struct vm_fault *vmf, struct vm_area_stru struct folio *folio, pte_t fault_pte, bool ignore_writable, bool pte_write_upgrade) { - int nr = pte_pfn(fault_pte) - folio_pfn(folio); + const unsigned long idx = pte_pfn(fault_pte) - folio_pfn(folio); unsigned long start, end, addr = vmf->address; - unsigned long addr_start = addr - (nr << PAGE_SHIFT); - unsigned long pt_start = ALIGN_DOWN(addr, PMD_SIZE); pte_t *start_ptep; - /* Stay within the VMA and within the page table. */ - start = max3(addr_start, pt_start, vma->vm_start); - end = min3(addr_start + folio_size(folio), pt_start + PMD_SIZE, - vma->vm_end); + folio_pte_range(folio, vma, addr, idx, &start, &end); start_ptep = vmf->pte - ((addr - start) >> PAGE_SHIFT); /* Restore all PTEs' mapping of the large folio */ --- base-commit: 634cbf5b794b734c78631b92e381cfc85f357bbe change-id: 20261013-folio_pte_scan_range-c6ca19cc8e9d -- Cheers, David