linux-kernel - Re: [PATCH v2 1/2] arm: kasan: support CONFIG_KASAN

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Date:   Mon, 14 Feb 2022 00:06:56 +0800
From:   Lecopzer Chen <lecopzer.chen@...iatek.com>
To:     <linus.walleij@...aro.org>
CC:     <andreyknvl@...il.com>, <anshuman.khandual@....com>,
        <ardb@...nel.org>, <arnd@...db.de>, <dvyukov@...gle.com>,
        <geert+renesas@...der.be>, <glider@...gle.com>,
        <kasan-dev@...glegroups.com>, <lecopzer.chen@...iatek.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux@...linux.org.uk>,
        <lukas.bulwahn@...il.com>, <mark.rutland@....com>,
        <masahiroy@...nel.org>, <matthias.bgg@...il.com>,
        <rmk+kernel@...linux.org.uk>, <ryabinin.a.a@...il.com>,
        <yj.chiang@...iatek.com>
Subject: Re: [PATCH v2 1/2] arm: kasan: support CONFIG_KASAN_VMALLOC

Hi Linus
 
Thanks for your review.
 
> > -       kasan_populate_early_shadow(kasan_mem_to_shadow((void *)VMALLOC_START),
> > +       if (!IS_ENABLED(CONFIG_KASAN_VMALLOC))
> > +               kasan_populate_early_shadow(kasan_mem_to_shadow((void *)VMALLOC_START),
> > +                                           kasan_mem_to_shadow((void *)VMALLOC_END));
> > +
> > +       kasan_populate_early_shadow(kasan_mem_to_shadow((void *)VMALLOC_END),
> >                                     kasan_mem_to_shadow((void *)-1UL) + 1);
> 
> Where is this actually mapped?
> 
> Can you print out where
> kasan_mem_to_shadow((void *)VMALLOC_START)
> kasan_mem_to_shadow((void *)VMALLOC_END)
> as well as KASAN_SHADOW_START and KASAN_SHADOW_END
> points?
> 
> When I looked into this getting the shadow memory between
> KASAN_SHADOW_START and KASAN_SHADOW_END
> seemed like the big problem since this is static, so how is Kasan
> solving this now?

For quick answer:
As I knwon, the definition of KASAN_SHADOW_START and END

(@arch/arm/include/asm/kasan_def.h)
* 1) KASAN_SHADOW_START
 *   This value begins with the MODULE_VADDR's shadow address. It is the
 *   start of kernel virtual space....
 *
 * 2) KASAN_SHADOW_END
 *   This value is the 0x100000000's shadow address: the mapping that would
 *   be after the end of the kernel memory at 0xffffffff....

and the virt address of vmalloc for ARM32 is also between MODULE_VADDR and
0x100000000 (ZONE_HIGHMEM), so nothing needs to do.

If there is any cases may break this assumption, please correct me, thanks.

> 
> Please patch the picture in
> include/asm/kasan_def.h
> and the info in
> Documentation/arm/memory.rst
> so it clearly reflects where VMALLOC is shadowed.

Thanks for suggestion, Yes, we really do need to update doc for memory layout.
I'll study how to add it and provide in v3.