Re: [PATCH v2 1/2] arm: kasan: support CONFIG_KASAN_VMALLOC

[Lecopzer Chen <lecopzer.chen@mediatek.com>]

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.