[PATCH 6.1.y 2/2] mm/hugetlb: fix mremap move length truncation

[Sasha Levin <sashal@kernel.org>]

From: Li Zhe <lizhe.67@bytedance.com>

[ Upstream commit dfb190302d2b4af86c6ae48af0d3b09f28b35460 ]

Patch series "mm/hugetlb: fix mremap bugs", v3.

This series fixes a few hugetlb mremap bugs.

Patch 1 fixes the return type of move_hugetlb_page_tables(), so large
hugetlb moves cannot be truncated when reported back to the generic
mremap code.

Patch 2 disables hugetlb PMD sharing for UFFD missing mode, so
UFFDIO_POISON markers cannot become visible through shared PMD page
tables.

Patch 3 fixes the recursive i_mmap_rwsem deadlock in the hugetlb mremap
path by avoiding the destination PMD sharing allocation path while the
mapping lock is already held for write.

This patch (of 3):

move_hugetlb_page_tables() returns the number of bytes moved, but
its return type is int while the generic move_page_tables() path uses
unsigned long lengths.

A hugetlb mremap() move length above INT_MAX can therefore be
misreported to copy_vma_and_data(). The out-of-range conversion to int
is implementation-defined; on common 64-bit builds, for example, a
4 GiB move can be reported as zero, making the caller treat the move as
a failure and use the wrong length for rollback.

Return unsigned long from move_hugetlb_page_tables(), matching
move_page_tables() and preserving the full byte count.

Link: https://lore.kernel.org/20261022034543.51226-1-lizhe.67@bytedance.com
Link: https://lore.kernel.org/20261022034543.51226-2-lizhe.67@bytedance.com
Fixes: 550a7d60bd5e ("mm, hugepages: add mremap() support for hugepage backed vma")
Signed-off-by: Li Zhe <lizhe.67@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Jose A. Perez de Azpillaga <azpijr@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/linux/hugetlb.h | 15 ++++++---------
 mm/hugetlb.c            |  7 +++----
 2 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index a9f175cda955c..86262b82ef8ad 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -137,10 +137,9 @@ void hugepage_put_subpool(struct hugepage_subpool *spool);
 
 void hugetlb_dup_vma_private(struct vm_area_struct *vma);
 void clear_vma_resv_huge_pages(struct vm_area_struct *vma);
-int move_hugetlb_page_tables(struct vm_area_struct *vma,
-			     struct vm_area_struct *new_vma,
-			     unsigned long old_addr, unsigned long new_addr,
-			     unsigned long len);
+unsigned long move_hugetlb_page_tables(struct vm_area_struct *vma,
+		struct vm_area_struct *new_vma, unsigned long old_addr,
+		unsigned long new_addr, unsigned long len);
 int copy_hugetlb_page_range(struct mm_struct *, struct mm_struct *,
 			    struct vm_area_struct *, struct vm_area_struct *);
 long follow_hugetlb_page(struct mm_struct *, struct vm_area_struct *,
@@ -296,11 +295,9 @@ static inline int copy_hugetlb_page_range(struct mm_struct *dst,
 	return 0;
 }
 
-static inline int move_hugetlb_page_tables(struct vm_area_struct *vma,
-					   struct vm_area_struct *new_vma,
-					   unsigned long old_addr,
-					   unsigned long new_addr,
-					   unsigned long len)
+static inline unsigned long move_hugetlb_page_tables(struct vm_area_struct *vma,
+		struct vm_area_struct *new_vma, unsigned long old_addr,
+		unsigned long new_addr, unsigned long len)
 {
 	BUG();
 	return 0;
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 459116c744a5a..a833a736c6ce9 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5304,10 +5304,9 @@ static void move_huge_pte(struct vm_area_struct *vma, unsigned long old_addr,
 	spin_unlock(dst_ptl);
 }
 
-int move_hugetlb_page_tables(struct vm_area_struct *vma,
-			     struct vm_area_struct *new_vma,
-			     unsigned long old_addr, unsigned long new_addr,
-			     unsigned long len)
+unsigned long move_hugetlb_page_tables(struct vm_area_struct *vma,
+		struct vm_area_struct *new_vma, unsigned long old_addr,
+		unsigned long new_addr, unsigned long len)
 {
 	struct hstate *h = hstate_vma(vma);
 	struct address_space *mapping = vma->vm_file->f_mapping;
-- 
2.53.0