From dc41e961a269f2ca4196e669d6d8e05480899cd4 Mon Sep 17 00:00:00 2001 From: Hui Su Date: Mon, 17 Aug 2026 20:08:00 +0800 Subject: [PATCH] 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 Cc: Alistair Popple Cc: Balbir Singh Cc: Byungchul Park Cc: David Hildenbrand Cc: Gregory Price Cc: "Huang, Ying" Cc: Joshua Hahn Cc: Matthew Brost Cc: Rakie Kim Cc: Zi Yan Cc: Signed-off-by: Andrew Morton --- mm/migrate_device.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) 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++)