Re: [PATCH v2 1/2] kasan: Refactor pcpu kasan vmalloc unpoison

[Andrey Konovalov <andreyknvl@gmail.com>]

On Tue, Dec 2, 2025 at 3:29 PM Maciej Wieczor-Retman
<m.wieczorretman@pm.me> wrote:
>
> From: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.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.
>
> 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.
>
> Fixes: 1d96320f8d53 ("kasan, vmalloc: add vmalloc tagging for SW_TAGS")
> Cc: <stable@vger.kernel.org> # 6.1+
> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
> ---
> Changelog v2:
> - Redo the whole patch so it's an actual refactor.
>
>  include/linux/kasan.h | 16 +++++++++++++---
>  mm/kasan/common.c     | 17 +++++++++++++++++
>  mm/kasan/hw_tags.c    | 15 +++++++++++++--
>  mm/kasan/shadow.c     | 16 ++++++++++++++--
>  mm/vmalloc.c          |  4 +---
>  5 files changed, 58 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index d12e1a5f5a9a..4a3d3dba9764 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -595,14 +595,14 @@ static inline void kasan_release_vmalloc(unsigned long start,
>
>  #endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
>
> -void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
> -                              kasan_vmalloc_flags_t flags);
> +void *__kasan_random_unpoison_vmalloc(const void *start, unsigned long size,
> +                                     kasan_vmalloc_flags_t flags);
>  static __always_inline void *kasan_unpoison_vmalloc(const void *start,
>                                                 unsigned long size,
>                                                 kasan_vmalloc_flags_t flags)
>  {
>         if (kasan_enabled())
> -               return __kasan_unpoison_vmalloc(start, size, flags);
> +               return __kasan_random_unpoison_vmalloc(start, size, flags);
>         return (void *)start;
>  }
>
> @@ -614,6 +614,11 @@ static __always_inline void kasan_poison_vmalloc(const void *start,
>                 __kasan_poison_vmalloc(start, size);
>  }
>
> +void *__kasan_unpoison_vmap_areas(void *addr, unsigned long size,
> +                                 kasan_vmalloc_flags_t flags, u8 tag);
> +void kasan_unpoison_vmap_areas(struct vm_struct **vms, int nr_vms,
> +                              kasan_vmalloc_flags_t flags);
> +
>  #else /* CONFIG_KASAN_VMALLOC */
>
>  static inline void kasan_populate_early_vm_area_shadow(void *start,
> @@ -638,6 +643,11 @@ 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..7884ea7d13f9 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)

kasan_unpoison_vmap_areas() needs to be defined in
inclunde/linux/kasan.h and call __kasan_unpoison_vmap_areas() when
kasan_enabled() == true, similar to the other wrappers.

And check my comment for patch #2: with that, you should not need to
add so many new __helpers: just __kasan_unpoison_vmalloc and
__kasan_unpoison_vmap_areas should suffice.


> +{
> +       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_vmap_areas(addr, size, flags);
> +       }
> +}
> +#endif
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index 1c373cc4b3fa..4b7936a2bd6f 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -316,8 +316,8 @@ static void init_vmalloc_pages(const void *start, unsigned long size)
>         }
>  }
>
> -void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
> -                               kasan_vmalloc_flags_t flags)
> +static void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
> +                                     kasan_vmalloc_flags_t flags)
>  {
>         u8 tag;
>         unsigned long redzone_start, redzone_size;
> @@ -387,6 +387,12 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
>         return (void *)start;
>  }
>
> +void *__kasan_random_unpoison_vmalloc(const void *start, unsigned long size,
> +                                     kasan_vmalloc_flags_t flags)
> +{
> +       return __kasan_unpoison_vmalloc(start, size, flags);
> +}
> +
>  void __kasan_poison_vmalloc(const void *start, unsigned long size)
>  {
>         /*
> @@ -396,6 +402,11 @@ void __kasan_poison_vmalloc(const void *start, unsigned long size)
>          */
>  }
>
> +void *__kasan_unpoison_vmap_areas(void *addr, unsigned long size,
> +                                 kasan_vmalloc_flags_t flags, u8 tag)
> +{
> +       return __kasan_unpoison_vmalloc(addr, size, flags);
> +}
>  #endif
>
>  void kasan_enable_hw_tags(void)
> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> index 5d2a876035d6..0a8d8bf6e9cf 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -624,8 +624,8 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
>         }
>  }
>
> -void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
> -                              kasan_vmalloc_flags_t flags)
> +static void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
> +                                     kasan_vmalloc_flags_t flags)
>  {
>         /*
>          * Software KASAN modes unpoison both VM_ALLOC and non-VM_ALLOC
> @@ -653,6 +653,18 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
>         return (void *)start;
>  }
>
> +void *__kasan_random_unpoison_vmalloc(const void *start, unsigned long size,
> +                                     kasan_vmalloc_flags_t flags)
> +{
> +       return __kasan_unpoison_vmalloc(start, size, flags);
> +}
> +
> +void *__kasan_unpoison_vmap_areas(void *addr, unsigned long size,
> +                                 kasan_vmalloc_flags_t flags, u8 tag)
> +{
> +       return __kasan_unpoison_vmalloc(addr, size, flags);
> +}
> +
>  /*
>   * Poison the shadow for a vmalloc region. Called as part of the
>   * freeing process at the time the region is freed.
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 798b2ed21e46..32ecdb8cd4b8 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -4870,9 +4870,7 @@ 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
>
>