Re: [PATCH] arm/kasan:fix the arry size of kasan_early_shadow_pte

From: Ard Biesheuvel <ardb@kernel.org>
To: Hailong liu <hailongliiu@yeah.net>,
	Linus Walleij <linus.walleij@linaro.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Ziliang Guo <guo.ziliang@zte.com.cn>,
	 Hailong Liu <liu.hailong6@zte.com.cn>,
	kasan-dev <kasan-dev@googlegroups.com>,
	 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	 Linux Memory Management List <linux-mm@kvack.org>,
	Alexander Potapenko <glider@google.com>,
	 Dmitry Vyukov <dvyukov@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	 Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Russell King <linux@armlinux.org.uk>
Subject: Re: [PATCH] arm/kasan:fix the arry size of kasan_early_shadow_pte
Date: Sat, 9 Jan 2021 09:51:19 +0100	[thread overview]
Message-ID: <CAMj1kXGBo_EBg+SYRd_cwPwQRq1NmRwJNyV6vjMMgA_S7Yff=A@mail.gmail.com> (raw)
In-Reply-To: <20210109044622.8312-1-hailongliiu@yeah.net>

(+ Linus)

On Sat, 9 Jan 2021 at 05:50, Hailong liu <hailongliiu@yeah.net> wrote:
>
> From: Hailong Liu <liu.hailong6@zte.com.cn>
>
> The size of kasan_early_shadow_pte[] now is PTRS_PER_PTE which defined to
> 512 for arm architecture. This means that it only covers the prev Linux pte
> entries, but not the HWTABLE pte entries for arm.
>
> The reason it works well current is that the symbol kasan_early_shadow_page
> immediately following kasan_early_shadow_pte in memory is page aligned,
> which makes kasan_early_shadow_pte look like a 4KB size array. But we can't
> ensure the order always right with different compiler/linker, nor more bss
> symbols be introduced.
>
> We had a test with QEMU + vexpress：put a 512KB-size symbol with attribute
> __section(".bss..page_aligned") after kasan_early_shadow_pte, and poison it
> after kasan_early_init(). Then enabled CONFIG_KASAN, it failed to boot up.
>
> Signed-off-by: Hailong Liu <liu.hailong6@zte.com.cn>
> Signed-off-by: Ziliang Guo <guo.ziliang@zte.com.cn>
> ---
>  include/linux/kasan.h | 6 +++++-
>  mm/kasan/init.c       | 3 ++-
>  2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 5e0655fb2a6f..fe1ae73ff8b5 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -35,8 +35,12 @@ struct kunit_kasan_expectation {
>  #define KASAN_SHADOW_INIT 0
>  #endif
>
> +#ifndef PTE_HWTABLE_PTRS
> +#define PTE_HWTABLE_PTRS 0
> +#endif
> +
>  extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
> -extern pte_t kasan_early_shadow_pte[PTRS_PER_PTE];
> +extern pte_t kasan_early_shadow_pte[PTRS_PER_PTE + PTE_HWTABLE_PTRS];
>  extern pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD];
>  extern pud_t kasan_early_shadow_pud[PTRS_PER_PUD];
>  extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
> diff --git a/mm/kasan/init.c b/mm/kasan/init.c
> index bc0ad208b3a7..7ca0b92d5886 100644
> --- a/mm/kasan/init.c
> +++ b/mm/kasan/init.c
> @@ -64,7 +64,8 @@ static inline bool kasan_pmd_table(pud_t pud)
>         return false;
>  }
>  #endif
> -pte_t kasan_early_shadow_pte[PTRS_PER_PTE] __page_aligned_bss;
> +pte_t kasan_early_shadow_pte[PTRS_PER_PTE + PTE_HWTABLE_PTRS]
> +       __page_aligned_bss;
>
>  static inline bool kasan_pte_table(pmd_t pmd)
>  {
> --
> 2.17.1
>
>
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