Merge tag 'mm-stable-2025-08-03-12-35' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Pull more MM updates from Andrew Morton:
 "Significant patch series in this pull request:

   - "mseal cleanups" (Lorenzo Stoakes)

     Some mseal cleaning with no intended functional change.

   - "Optimizations for khugepaged" (David Hildenbrand)

     Improve khugepaged throughput by batching PTE operations for large
     folios. This gain is mainly for arm64.

   - "x86: enable EXECMEM_ROX_CACHE for ftrace and kprobes" (Mike Rapoport)

     A bugfix, additional debug code and cleanups to the execmem code.

   - "mm/shmem, swap: bugfix and improvement of mTHP swap in" (Kairui Song)

     Bugfixes, cleanups and performance improvememnts to the mTHP swapin
     code"

* tag 'mm-stable-2025-08-03-12-35' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (38 commits)
  mm: mempool: fix crash in mempool_free() for zero-minimum pools
  mm: correct type for vmalloc vm_flags fields
  mm/shmem, swap: fix major fault counting
  mm/shmem, swap: rework swap entry and index calculation for large swapin
  mm/shmem, swap: simplify swapin path and result handling
  mm/shmem, swap: never use swap cache and readahead for SWP_SYNCHRONOUS_IO
  mm/shmem, swap: tidy up swap entry splitting
  mm/shmem, swap: tidy up THP swapin checks
  mm/shmem, swap: avoid redundant Xarray lookup during swapin
  x86/ftrace: enable EXECMEM_ROX_CACHE for ftrace allocations
  x86/kprobes: enable EXECMEM_ROX_CACHE for kprobes allocations
  execmem: drop writable parameter from execmem_fill_trapping_insns()
  execmem: add fallback for failures in vmalloc(VM_ALLOW_HUGE_VMAP)
  execmem: move execmem_force_rw() and execmem_restore_rox() before use
  execmem: rework execmem_cache_free()
  execmem: introduce execmem_alloc_rw()
  execmem: drop unused execmem_update_copy()
  mm: fix a UAF when vma->mm is freed after vma->vm_refcnt got dropped
  mm/rmap: add anon_vma lifetime debug check
  mm: remove mm/io-mapping.c
  ...

1 files changed, 18 insertions, 7 deletions

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index ed4873e18c75..9142964ab9c9 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -230,16 +230,12 @@ static bool check_slab_allocation(struct kmem_cache *cache, void *object,
 }
 
 static inline void poison_slab_object(struct kmem_cache *cache, void *object,
-				      bool init, bool still_accessible)
+				      bool init)
 {
 	void *tagged_object = object;
 
 	object = kasan_reset_tag(object);
 
-	/* RCU slabs could be legally used after free within the RCU period. */
-	if (unlikely(still_accessible))
-		return;
-
 	kasan_poison(object, round_up(cache->object_size, KASAN_GRANULE_SIZE),
 			KASAN_SLAB_FREE, init);
 
@@ -261,7 +257,22 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object, bool init,
 	if (!kasan_arch_is_ready() || is_kfence_address(object))
 		return false;
 
-	poison_slab_object(cache, object, init, still_accessible);
+	/*
+	 * If this point is reached with an object that must still be
+	 * accessible under RCU, we can't poison it; in that case, also skip the
+	 * quarantine. This should mostly only happen when CONFIG_SLUB_RCU_DEBUG
+	 * has been disabled manually.
+	 *
+	 * Putting the object on the quarantine wouldn't help catch UAFs (since
+	 * we can't poison it here), and it would mask bugs caused by
+	 * SLAB_TYPESAFE_BY_RCU users not being careful enough about object
+	 * reuse; so overall, putting the object into the quarantine here would
+	 * be counterproductive.
+	 */
+	if (still_accessible)
+		return false;
+
+	poison_slab_object(cache, object, init);
 
 	/*
 	 * If the object is put into quarantine, do not let slab put the object
@@ -519,7 +530,7 @@ bool __kasan_mempool_poison_object(void *ptr, unsigned long ip)
 	if (check_slab_allocation(slab->slab_cache, ptr, ip))
 		return false;
 
-	poison_slab_object(slab->slab_cache, ptr, false, false);
+	poison_slab_object(slab->slab_cache, ptr, false);
 	return true;
 }