linux-kernel - [PATCH v4 2/3] kasan: Refactor pcpu kasan vmalloc unpoison

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Message-ID: <6dd6a10f94241cef935fec58c312cb846d352490.1764945396.git.m.wieczorretman@pm.me>
Date: Fri, 05 Dec 2025 14:59:17 +0000
From: Maciej Wieczor-Retman <m.wieczorretman@...me>
To: Andrey Ryabinin <ryabinin.a.a@...il.com>, Alexander Potapenko <glider@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>, Vincenzo Frascino <vincenzo.frascino@....com>, Andrew Morton <akpm@...ux-foundation.org>, Uladzislau Rezki <urezki@...il.com>, Marco Elver <elver@...gle.com>
Cc: jiayuan.chen@...ux.dev, m.wieczorretman@...me, stable@...r.kernel.org, Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>, kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH v4 2/3] kasan: Refactor pcpu kasan vmalloc unpoison

From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>

A KASAN tag mismatch, possibly causing a kernel panic, can be observed
on systems with a tag-based KASAN enabled and with multiple NUMA nodes.
It was reported on arm64 and reproduced on x86. It can be explained in
the following points:

	1. There can be more than one virtual memory chunk.
	2. Chunk's base address has a tag.
	3. The base address points at the first chunk and thus inherits
	   the tag of the first chunk.
	4. The subsequent chunks will be accessed with the tag from the
	   first chunk.
	5. Thus, the subsequent chunks need to have their tag set to
	   match that of the first chunk.

Refactor code by reusing __kasan_unpoison_vmalloc in a new helper in
preparation for the actual fix.

Fixes: 1d96320f8d53 ("kasan, vmalloc: add vmalloc tagging for SW_TAGS")
Cc: stable@...r.kernel.org # 6.1+
Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
Reviewed-by: Andrey Konovalov <andreyknvl@...il.com>
---
Changelog v1: (after splitting of from the KASAN series)
- Rewrite first paragraph of the patch message to point at the user
  impact of the issue.
- Move helper to common.c so it can be compiled in all KASAN modes.

Changelog v2:
- Redo the whole patch so it's an actual refactor.

Changelog v3:
- Redo the patch after applying Andrey's comments to align the code more
  with what's already in include/linux/kasan.h

 include/linux/kasan.h | 15 +++++++++++++++
 mm/kasan/common.c     | 17 +++++++++++++++++
 mm/vmalloc.c          |  4 +---
 3 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 6d7972bb390c..cde493cb7702 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -615,6 +615,16 @@ static __always_inline void kasan_poison_vmalloc(const void *start,
 		__kasan_poison_vmalloc(start, size);
 }
 
+void __kasan_unpoison_vmap_areas(struct vm_struct **vms, int nr_vms,
+				 kasan_vmalloc_flags_t flags);
+static __always_inline void
+kasan_unpoison_vmap_areas(struct vm_struct **vms, int nr_vms,
+			  kasan_vmalloc_flags_t flags)
+{
+	if (kasan_enabled())
+		__kasan_unpoison_vmap_areas(vms, nr_vms, flags);
+}
+
 #else /* CONFIG_KASAN_VMALLOC */
 
 static inline void kasan_populate_early_vm_area_shadow(void *start,
@@ -639,6 +649,11 @@ static inline void *kasan_unpoison_vmalloc(const void *start,
 static inline void kasan_poison_vmalloc(const void *start, unsigned long size)
 { }
 
+static __always_inline void
+kasan_unpoison_vmap_areas(struct vm_struct **vms, int nr_vms,
+			  kasan_vmalloc_flags_t flags)
+{ }
+
 #endif /* CONFIG_KASAN_VMALLOC */
 
 #if (defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)) && \
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index d4c14359feaf..1ed6289d471a 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -28,6 +28,7 @@
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/bug.h>
+#include <linux/vmalloc.h>
 
 #include "kasan.h"
 #include "../slab.h"
@@ -582,3 +583,19 @@ bool __kasan_check_byte(const void *address, unsigned long ip)
 	}
 	return true;
 }
+
+#ifdef CONFIG_KASAN_VMALLOC
+void __kasan_unpoison_vmap_areas(struct vm_struct **vms, int nr_vms,
+				 kasan_vmalloc_flags_t flags)
+{
+	unsigned long size;
+	void *addr;
+	int area;
+
+	for (area = 0 ; area < nr_vms ; area++) {
+		size = vms[area]->size;
+		addr = vms[area]->addr;
+		vms[area]->addr = __kasan_unpoison_vmalloc(addr, size, flags);
+	}
+}
+#endif
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 22a73a087135..33e705ccafba 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4872,9 +4872,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
 	 * With hardware tag-based KASAN, marking is skipped for
 	 * non-VM_ALLOC mappings, see __kasan_unpoison_vmalloc().
 	 */
-	for (area = 0; area < nr_vms; area++)
-		vms[area]->addr = kasan_unpoison_vmalloc(vms[area]->addr,
-				vms[area]->size, KASAN_VMALLOC_PROT_NORMAL);
+	kasan_unpoison_vmap_areas(vms, nr_vms, KASAN_VMALLOC_PROT_NORMAL);
 
 	kfree(vas);
 	return vms;
-- 
2.52.0