linux-kernel - [PATCH v6 02/18] kasan: Unpoison vms[area] addresses with a common tag

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Message-ID: <932121edc75be8e2038d64ecb4853df2e2b258df.1761763681.git.m.wieczorretman@pm.me>
Date: Wed, 29 Oct 2025 19:06:03 +0000
From: Maciej Wieczor-Retman <m.wieczorretman@...me>
To: xin@...or.com, peterz@...radead.org, kaleshsingh@...gle.com, kbingham@...nel.org, akpm@...ux-foundation.org, nathan@...nel.org, ryabinin.a.a@...il.com, dave.hansen@...ux.intel.com, bp@...en8.de, morbo@...gle.com, jeremy.linton@....com, smostafa@...gle.com, kees@...nel.org, baohua@...nel.org, vbabka@...e.cz, justinstitt@...gle.com, wangkefeng.wang@...wei.com, leitao@...ian.org, jan.kiszka@...mens.com, fujita.tomonori@...il.com, hpa@...or.com, urezki@...il.com, ubizjak@...il.com, ada.coupriediaz@....com, nick.desaulniers+lkml@...il.com, ojeda@...nel.org, brgerst@...il.com, elver@...gle.com, pankaj.gupta@....com, glider@...gle.com, mark.rutland@....com, trintaeoitogc@...il.com, jpoimboe@...nel.org, thuth@...hat.com, pasha.tatashin@...een.com, dvyukov@...gle.com, jhubbard@...dia.com, catalin.marinas@....com, yeoreum.yun@....com, mhocko@...e.com, lorenzo.stoakes@...cle.com, samuel.holland@...ive.com, vincenzo.frascino@....com, bigeasy@...utronix.de, surenb@...gle.com,
	ardb@...nel.org, Liam.Howlett@...cle.com, nicolas.schier@...ux.dev, ziy@...dia.com, kas@...nel.org, tglx@...utronix.de, mingo@...hat.com, broonie@...nel.org, corbet@....net, andreyknvl@...il.com, maciej.wieczor-retman@...el.com, david@...hat.com, maz@...nel.org, rppt@...nel.org, will@...nel.org, luto@...nel.org
Cc: kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, x86@...nel.org, linux-kbuild@...r.kernel.org, linux-mm@...ck.org, llvm@...ts.linux.dev, linux-doc@...r.kernel.org, m.wieczorretman@...me, stable@...r.kernel.org, Baoquan He <bhe@...hat.com>
Subject: [PATCH v6 02/18] kasan: Unpoison vms[area] addresses with a common tag

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

The problem presented here is related to NUMA systems and tag-based
KASAN modes - software and hardware ones. 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.

Unpoison all vms[]->addr memory and pointers with the same tag to
resolve the mismatch.

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>
Tested-by: Baoquan He <bhe@...hat.com>
---
Changelog v6:
- Add Baoquan's tested-by tag.
- Move patch to the beginning of the series as it is a fix.
- Add fixes tag.

 mm/kasan/tags.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index ecc17c7c675a..c6b40cbffae3 100644
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -148,12 +148,20 @@ void __kasan_save_free_info(struct kmem_cache *cache, void *object)
 	save_stack_info(cache, object, 0, true);
 }
 
+/*
+ * A tag mismatch happens when calculating per-cpu chunk addresses, because
+ * they all inherit the tag from vms[0]->addr, even when nr_vms is bigger
+ * than 1. This is a problem because all the vms[]->addr come from separate
+ * allocations and have different tags so while the calculated address is
+ * correct the tag isn't.
+ */
 void __kasan_unpoison_vmap_areas(struct vm_struct **vms, int nr_vms)
 {
 	int area;
 
 	for (area = 0 ; area < nr_vms ; area++) {
 		kasan_poison(vms[area]->addr, vms[area]->size,
-			     arch_kasan_get_tag(vms[area]->addr), false);
+			     arch_kasan_get_tag(vms[0]->addr), false);
+		arch_kasan_set_tag(vms[area]->addr, arch_kasan_get_tag(vms[0]->addr));
 	}
 }
-- 
2.51.0