The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x 6a0e5b333842cf65d6f4e4f0a2a4386504802515 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2026010532-stained-crumpet-3d80@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 6a0e5b333842cf65d6f4e4f0a2a4386504802515 Mon Sep 17 00:00:00 2001 From: Maciej Wieczor-Retman maciej.wieczor-retman@intel.com Date: Thu, 4 Dec 2025 19:00:11 +0000 Subject: [PATCH] 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-xY36kxVdFvwmag2Z... [maciej.wieczor-retman@intel.com: remove unneeded pr_warn()] Link: https://lkml.kernel.org/r/919897daaaa3c982a27762a2ee038769ad033991.176494539... Link: https://lkml.kernel.org/r/873821114a9f722ffb5d6702b94782e902883fdf.176487457... 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;

- for (area = 0 ; area < nr_vms ; area++) { + /* + * 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 = 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