From: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
Date: Thu, 4 Dec 2025 19:00:11 +0000 (+0000)
Subject: kasan: unpoison vms[area] addresses with a common tag
X-Git-Tag: v6.19-rc4~22^2~20
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6a0e5b333842cf65d6f4e4f0a2a4386504802515;p=thirdparty%2Flinux.git

kasan: unpoison vms[area] addresses with a common tag

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.

Use the new vmalloc flag that disables random tag assignment in
__kasan_unpoison_vmalloc() - pass the same random tag to all the
vm_structs by tagging the pointers before they go inside
__kasan_unpoison_vmalloc().  Assigning a common tag resolves the pcpu
chunk address mismatch.

[akpm@linux-foundation.org: use WARN_ON_ONCE(), per Andrey]
  Link: https://lkml.kernel.org/r/CA+fCnZeuGdKSEm11oGT6FS71_vGq1vjq-xY36kxVdFvwmag2ZQ@mail.gmail.com
[maciej.wieczor-retman@intel.com: remove unneeded pr_warn()]
  Link: https://lkml.kernel.org/r/919897daaaa3c982a27762a2ee038769ad033991.1764945396.git.m.wieczorretman@pm.me
Link: https://lkml.kernel.org/r/873821114a9f722ffb5d6702b94782e902883fdf.1764874575.git.m.wieczorretman@pm.me
Fixes: 1d96320f8d53 ("kasan, vmalloc: add vmalloc tagging for SW_TAGS")
Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
Cc: Kees Cook <kees@kernel.org>
Cc: Marco Elver <elver@google.com>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: <stable@vger.kernel.org>	[6.1+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index b2b40c59ce18..ed489a14dddf 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -584,11 +584,26 @@ void __kasan_unpoison_vmap_areas(struct vm_struct **vms, int nr_vms,
 	unsigned long size;
 	void *addr;
 	int area;
+	u8 tag;
+
+	/*
+	 * If KASAN_VMALLOC_KEEP_TAG was set at this point, all vms[] pointers
+	 * would be unpoisoned with the KASAN_TAG_KERNEL which would disable
+	 * KASAN checks down the line.
+	 */
+	if (WARN_ON_ONCE(flags & KASAN_VMALLOC_KEEP_TAG))
+		return;
+
+	size = vms[0]->size;
+	addr = vms[0]->addr;
+	vms[0]->addr = __kasan_unpoison_vmalloc(addr, size, flags);
+	tag = get_tag(vms[0]->addr);
 
-	for (area = 0 ; area < nr_vms ; area++) {
+	for (area = 1 ; area < nr_vms ; area++) {
 		size = vms[area]->size;
-		addr = vms[area]->addr;
-		vms[area]->addr = __kasan_unpoison_vmalloc(addr, size, flags);
+		addr = set_tag(vms[area]->addr, tag);
+		vms[area]->addr =
+			__kasan_unpoison_vmalloc(addr, size, flags | KASAN_VMALLOC_KEEP_TAG);
 	}
 }
 #endif