mm/migrate_device: avoid out-of-bounds writes for compound folios

migrate_device_range() and migrate_device_pfns() clear the entries
following a compound folio so that the PFN arrays retain their
page-granular representation.

If a compound folio extends beyond the end of the caller-provided range,
the loops clear all following folio entries without limiting them to the
number of slots remaining in the npages-sized array, causing an
out-of-bounds write.

Do not proceed with a compound folio if its page-granular representation
does not fit entirely in the remaining PFN array.  If this happens, drop
any reference and lock acquired for the folio, clear the remaining
entries, and stop collecting.

Observed with a KASAN x86 QEMU kernel using the HMM migrate_anon_huge_zero
selftest.  Closing /dev/hmm_dmirror0 after migrating an anonymous huge
page to device memory exercises:

  dmirror_fops_release()
    -> dmirror_device_evict_chunk()
      -> migrate_device_range()

Link: https://lore.kernel.org/20260817120758.669807-3-sh_def@163.com
Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
Signed-off-by: Hui Su <sh_def@163.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Balbir Singh <balbirs@nvidia.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Gregory Price <gourry@gourry.net>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 762c5cee8fec..009bfa8b212d 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -1423,6 +1423,15 @@ int migrate_device_range(unsigned long *src_pfns, unsigned long start,
 
 		src_pfns[i] = migrate_device_pfn_lock(pfn);
 		nr = folio_nr_pages(folio);
+		if (nr > npages - i) {
+			if (src_pfns[i] & MIGRATE_PFN_MIGRATE) {
+				folio_unlock(folio);
+				folio_put(folio);
+			}
+			memset(&src_pfns[i], 0,
+			       (npages - i) * sizeof(*src_pfns));
+			break;
+		}
 		if (nr > 1) {
 			src_pfns[i] |= MIGRATE_PFN_COMPOUND;
 			for (j = 1; j < nr; j++)
@@ -1457,6 +1466,15 @@ int migrate_device_pfns(unsigned long *src_pfns, unsigned long npages)
 
 		src_pfns[i] = migrate_device_pfn_lock(src_pfns[i]);
 		nr = folio_nr_pages(folio);
+		if (nr > npages - i) {
+			if (src_pfns[i] & MIGRATE_PFN_MIGRATE) {
+				folio_unlock(folio);
+				folio_put(folio);
+			}
+			memset(&src_pfns[i], 0,
+			       (npages - i) * sizeof(*src_pfns));
+			break;
+		}
 		if (nr > 1) {
 			src_pfns[i] |= MIGRATE_PFN_COMPOUND;
 			for (j = 1; j < nr; j++)