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mm: fix address wraparound when scanning large folio PTEs

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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.

Link: https://lore.kernel.org/20261014-folio_pte_scan_range-v2-1-00cf9bbaa364@kernel.org
Fixes: d2136d749d ("mm: support multi-size THP numa balancing")
Fixes: 508758960b ("mm: swap: entirely map large folios found in swapcache")
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Kyle Zeng <kylebot@openai.com>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Barry Song <baohua@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Ying Huang <huang.ying.caritas@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Chuanhua Han <hanchuanhua@oppo.com>
Cc: <stable@vger.kernel.org>
This commit is contained in:
David Hildenbrand (Arm) 2026-10-14 20:34:28 +02:00 committed by Andrew Morton
parent 854e5ff8b3
commit f681d4580d
1 changed files with 36 additions and 14 deletions
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50
mm/memory.c
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@ -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 */