linux-hardening - Re: [PATCH] LoongArch: Add kernel address sanitizer support

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Message-ID: <CA+fCnZevgYh7CzJ9gOWJ80SwY4Y9w8UO2ZiFAXEnAhQhFgrffA@mail.gmail.com>
Date:   Wed, 29 Mar 2023 21:02:39 +0200
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Qing Zhang <zhangqing@...ngson.cn>
Cc:     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,
        Andrey Ryabinin <ryabinin.a.a@...il.com>
Subject: Re: [PATCH] LoongArch: Add kernel address sanitizer support

> 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/generic.c b/mm/kasan/generic.c
> index e5eef670735e..f86194750df5 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -175,6 +175,11 @@ static __always_inline bool check_region_inline(unsigned long addr,
>         if (unlikely(!addr_has_metadata((void *)addr)))
>                 return !kasan_report(addr, size, write, ret_ip);
>
> +#ifndef __HAVE_ARCH_SHADOW_MAP
> +       if (unlikely(kasan_mem_to_shadow((unsigned long *)addr) == NULL))
> +               return !kasan_report(addr, size, write, ret_ip);
> +#endif

This should have been ifdef, right?

But I don't think you need this check here at all: addr_has_metadata
already checks that shadow exists.

> +
>         if (likely(!memory_is_poisoned(addr, size)))
>                 return true;
>
> diff --git a/mm/kasan/init.c b/mm/kasan/init.c
> index cc64ed6858c6..860061a22ca9 100644
> --- a/mm/kasan/init.c
> +++ b/mm/kasan/init.c
> @@ -166,8 +166,9 @@ static int __ref zero_pud_populate(p4d_t *p4d, unsigned long addr,
>                                 if (!p)
>                                         return -ENOMEM;
>                         } else {
> -                               pud_populate(&init_mm, pud,
> -                                       early_alloc(PAGE_SIZE, NUMA_NO_NODE));
> +                               p = early_alloc(PAGE_SIZE, NUMA_NO_NODE);
> +                               pmd_init(p);
> +                               pud_populate(&init_mm, pud, p);
>                         }
>                 }
>                 zero_pmd_populate(pud, addr, next);
> @@ -207,8 +208,9 @@ static int __ref zero_p4d_populate(pgd_t *pgd, unsigned long addr,
>                                 if (!p)
>                                         return -ENOMEM;
>                         } else {
> -                               p4d_populate(&init_mm, p4d,
> -                                       early_alloc(PAGE_SIZE, NUMA_NO_NODE));
> +                               p = early_alloc(PAGE_SIZE, NUMA_NO_NODE);
> +                               pud_init(p);
> +                               p4d_populate(&init_mm, p4d, p);

Please explain why these changes are needed in the patch description.

>                         }
>                 }
>                 zero_pud_populate(p4d, addr, next);
> 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
>