mm/userfaultfd: fix hugetlb fault mutex hash calculation

commit 0217c7fb4de4a40cee667eb21901f3204effe5ac upstream.

In mfill_atomic_hugetlb(), linear_page_index() is used to calculate the
page index for hugetlb_fault_mutex_hash().  However, linear_page_index()
returns the index in PAGE_SIZE units, while hugetlb_fault_mutex_hash()
expects the index in huge page units.  This mismatch means that different
addresses within the same huge page can produce different hash values,
leading to the use of different mutexes for the same huge page.  This can
cause races between faulting threads, which can corrupt the reservation
map and trigger the BUG_ON in resv_map_release().

Fix this by introducing hugetlb_linear_page_index(), which returns the
page index in huge page granularity, and using it in place of
linear_page_index().

Link: https://lkml.kernel.org/r/20260310110526.335749-1-jianhuizzzzz@gmail.com
Fixes: a08c7193e4f1 ("mm/filemap: remove hugetlb special casing in filemap.c")
Signed-off-by: Jianhui Zhou <jianhuizzzzz@gmail.com>
Reported-by: syzbot+f525fd79634858f478e7@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f525fd79634858f478e7
Acked-by: SeongJae Park <sj@kernel.org>
Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: JonasZhou <JonasZhou@zhaoxin.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 65910437be1ca3964e5e8c6745d197d16612c2a3..67d4f092464649e2500521b2ee689e1d744e53c3 100644 (file)
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -796,6 +796,23 @@ static inline unsigned huge_page_shift(struct hstate *h)
        return h->order + PAGE_SHIFT;
 }
 
+/**
+ * hugetlb_linear_page_index() - linear_page_index() but in hugetlb
+ *                              page size granularity.
+ * @vma: the hugetlb VMA
+ * @address: the virtual address within the VMA
+ *
+ * Return: the page offset within the mapping in huge page units.
+ */
+static inline pgoff_t hugetlb_linear_page_index(struct vm_area_struct *vma,
+               unsigned long address)
+{
+       struct hstate *h = hstate_vma(vma);
+
+       return ((address - vma->vm_start) >> huge_page_shift(h)) +
+               (vma->vm_pgoff >> huge_page_order(h));
+}
+
 static inline bool order_is_gigantic(unsigned int order)
 {
        return order > MAX_PAGE_ORDER;

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 927086bb4a3c2e57b9c787d87fd4b63e2b2f32e8..5590989e18c7461389e40c6a9871f130c098b311 100644 (file)
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -573,7 +573,7 @@ retry:
                 * in the case of shared pmds.  fault mutex prevents
                 * races with other faulting threads.
                 */
-               idx = linear_page_index(dst_vma, dst_addr);
+               idx = hugetlb_linear_page_index(dst_vma, dst_addr);
                mapping = dst_vma->vm_file->f_mapping;
                hash = hugetlb_fault_mutex_hash(mapping, idx);
                mutex_lock(&hugetlb_fault_mutex_table[hash]);