linux-hardening - Re: [PATCH v2 4/6] kasan: Add __HAVE_ARCH_SHADOW

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Date:   Wed, 5 Apr 2023 00:09:38 +0200
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Qing Zhang <zhangqing@...ngson.cn>
Cc:     Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Huacai Chen <chenhuacai@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        WANG Xuerui <kernel@...0n.name>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        kasan-dev@...glegroups.com, linux-doc@...r.kernel.org,
        linux-mm@...ck.org, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 4/6] kasan: Add __HAVE_ARCH_SHADOW_MAP to support arch
 specific mapping

On Tue, Apr 4, 2023 at 10:43 AM Qing Zhang <zhangqing@...ngson.cn> wrote:
>
> Like the LoongArch, which has many holes between different segments
> and valid address space(256T available) is insufficient to map all
> these segments to kasan shadow memory with the common formula provided
> by kasan core, We need architecture specific mapping formula,different
> segments are mapped individually, and only limited length of space of
> that specific segment is mapped to shadow.
>
> Therefore, when the incoming address is converted to a shadow, we need
> to add a condition to determine whether it is valid.
>
> Signed-off-by: Qing Zhang <zhangqing@...ngson.cn>
> ---
>  include/linux/kasan.h | 2 ++
>  mm/kasan/kasan.h      | 6 ++++++
>  2 files changed, 8 insertions(+)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index f7ef70661ce2..3b91b941873d 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -54,11 +54,13 @@ extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
>  int kasan_populate_early_shadow(const void *shadow_start,
>                                 const void *shadow_end);
>
> +#ifndef __HAVE_ARCH_SHADOW_MAP
>  static inline void *kasan_mem_to_shadow(const void *addr)
>  {
>         return (void *)((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT)
>                 + KASAN_SHADOW_OFFSET;
>  }
> +#endif
>
>  int kasan_add_zero_shadow(void *start, unsigned long size);
>  void kasan_remove_zero_shadow(void *start, unsigned long size);
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index a61eeee3095a..033335c13b25 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -291,16 +291,22 @@ struct kasan_stack_ring {
>
>  #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
>
> +#ifndef __HAVE_ARCH_SHADOW_MAP
>  static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
>  {
>         return (void *)(((unsigned long)shadow_addr - KASAN_SHADOW_OFFSET)
>                 << KASAN_SHADOW_SCALE_SHIFT);
>  }
> +#endif
>
>  static __always_inline bool addr_has_metadata(const void *addr)
>  {
> +#ifdef __HAVE_ARCH_SHADOW_MAP
> +       return (kasan_mem_to_shadow((void *)addr) != NULL);
> +#else
>         return (kasan_reset_tag(addr) >=
>                 kasan_shadow_to_mem((void *)KASAN_SHADOW_START));
> +#endif
>  }
>
>  /**
> --
> 2.20.1
>

Reviewed-by: Andrey Konovalov <andreyknvl@...il.com>

Thanks!