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

From: Linus Walleij <linus.walleij@linaro.org>
To: Hailong liu <hailongliiu@yeah.net>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Ziliang Guo <guo.ziliang@zte.com.cn>,
	 Hailong Liu <liu.hailong6@zte.com.cn>,
	Russell King <linux@armlinux.org.uk>,
	 kasan-dev <kasan-dev@googlegroups.com>,
	 "linux-kernel@vger.kernel.org" <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>
Subject: Re: [PATCH] arm/kasan:fix the arry size of kasan_early_shadow_pte
Date: Sat, 9 Jan 2021 22:26:08 +0100	[thread overview]
Message-ID: <CACRpkdb73diprma9Z1-4nm5A9OTQMeGVK=Hcqiwny9VOVdA=QQ@mail.gmail.com> (raw)
In-Reply-To: <20210109044622.8312-1-hailongliiu@yeah.net>

On Sat, Jan 9, 2021 at 5:51 AM 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>

OK I see the problem, I think.

> +#ifndef PTE_HWTABLE_PTRS
> +#define PTE_HWTABLE_PTRS 0
> +#endif

Can this even happen? We have either pgtable-2level.h or
pgtable-3level.h, both of which define PTE_HWTABLE_PTRS.

>  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];

Yeah this looks exactly like bm_pte so it makes sense.

If you drop the first ifndef,
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij