linux-kernel - [PATCH v1 3/5] mm: Take into account mm_cid size for mm

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Message-Id: <20251221232926.450602-4-mathieu.desnoyers@efficios.com>
Date: Sun, 21 Dec 2025 18:29:24 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Mark Brown <broonie@...nel.org>,
	linux-mm@...ck.org,
	Thomas Gleixner <tglx@...utronix.de>,
	stable@...r.kernel.org
Subject: [PATCH v1 3/5] mm: Take into account mm_cid size for mm_struct static definitions

Both init_mm and efi_mm static definitions need to make room for the
2 mm_cid cpumasks.

This fixes possible out-of-bounds accesses to init_mm and efi_mm.

Fixes: af7f588d8f73 ("sched: Introduce per-memory-map concurrency ID")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Mark Brown <broonie@...nel.org>
Cc: stable@...r.kernel.org
Cc: linux-mm@...ck.org
---
 include/linux/mm_types.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 1531df8cda52..aefa64db3499 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1368,7 +1368,7 @@ extern struct mm_struct init_mm;
 
 #define MM_STRUCT_FLEXIBLE_ARRAY_INIT				\
 {								\
-	[0 ... sizeof(cpumask_t)-1] = 0				\
+	[0 ... sizeof(cpumask_t) + MM_CID_STATIC_SIZE - 1] = 0	\
 }
 
 /* Pointer magic because the dynamic array size confuses some compilers. */
@@ -1500,7 +1500,7 @@ static inline int mm_alloc_cid_noprof(struct mm_struct *mm, struct task_struct *
 	mm_init_cid(mm, p);
 	return 0;
 }
-#define mm_alloc_cid(...)	alloc_hooks(mm_alloc_cid_noprof(__VA_ARGS__))
+# define mm_alloc_cid(...)	alloc_hooks(mm_alloc_cid_noprof(__VA_ARGS__))
 
 static inline void mm_destroy_cid(struct mm_struct *mm)
 {
@@ -1514,6 +1514,8 @@ static inline unsigned int mm_cid_size(void)
 	return cpumask_size() + bitmap_size(num_possible_cpus());
 }
 
+/* Use NR_CPUS as worse case for static allocation. */
+# define MM_CID_STATIC_SIZE	(2 * sizeof(cpumask_t))
 #else /* CONFIG_SCHED_MM_CID */
 static inline void mm_init_cid(struct mm_struct *mm, struct task_struct *p) { }
 static inline int mm_alloc_cid(struct mm_struct *mm, struct task_struct *p) { return 0; }
@@ -1522,6 +1524,7 @@ static inline unsigned int mm_cid_size(void)
 {
 	return 0;
 }
+# define MM_CID_STATIC_SIZE	0
 #endif /* CONFIG_SCHED_MM_CID */
 
 struct mmu_gather;
-- 
2.39.5