linux-kernel - Re: [PATCH -next 3/3] kasan: arm64: Fix pcpu_page_first_chunk crash with KASAN

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Date:   Mon, 5 Jul 2021 17:04:16 +0200
From:   Marco Elver <elver@...gle.com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        Daniel Axtens <dja@...ens.net>
Subject: Re: [PATCH -next 3/3] kasan: arm64: Fix pcpu_page_first_chunk crash
 with KASAN_VMALLOC

On Mon, Jul 05, 2021 at 07:14PM +0800, Kefeng Wang wrote:
[...]
> +#ifdef CONFIG_KASAN_VMALLOC
> +void __init __weak kasan_populate_early_vm_area_shadow(void *start,
> +						       unsigned long size)

This should probably not be __weak, otherwise you now have 2 __weak
functions.

> +{
> +	unsigned long shadow_start, shadow_end;
> +
> +	if (!is_vmalloc_or_module_addr(start))
> +		return;
> +
> +	shadow_start = (unsigned long)kasan_mem_to_shadow(start);
> +	shadow_start = ALIGN_DOWN(shadow_start, PAGE_SIZE);
> +	shadow_end = (unsigned long)kasan_mem_to_shadow(start + size);
> +	shadow_end = ALIGN(shadow_end, PAGE_SIZE);
> +	kasan_map_populate(shadow_start, shadow_end,
> +			   early_pfn_to_nid(virt_to_pfn(start)));
> +}
> +#endif

This function looks quite generic -- would any of this also apply to
other architectures? I see that ppc and sparc at least also define
CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK.

>  void __init kasan_init(void)
>  {
>  	kasan_init_shadow();
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 5310e217bd74..79d3895b0240 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -49,6 +49,8 @@ extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
>  int kasan_populate_early_shadow(const void *shadow_start,
>  				const void *shadow_end);
>  
> +void kasan_populate_early_vm_area_shadow(void *start, unsigned long size);
> +
>  static inline void *kasan_mem_to_shadow(const void *addr)
>  {
>  	return (void *)((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT)
> diff --git a/mm/kasan/init.c b/mm/kasan/init.c
> index cc64ed6858c6..d39577d088a1 100644
> --- a/mm/kasan/init.c
> +++ b/mm/kasan/init.c
> @@ -279,6 +279,11 @@ int __ref kasan_populate_early_shadow(const void *shadow_start,
>  	return 0;
>  }
>  
> +void __init __weak kasan_populate_early_vm_area_shadow(void *start,
> +						       unsigned long size)
> +{
> +}

I'm just wondering if this could be a generic function, perhaps with an
appropriate IS_ENABLED() check of a generic Kconfig option
(CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK ?) to short-circuit it, if it's
not only an arm64 problem.

But I haven't looked much further, so would appeal to you to either
confirm or reject this idea.

Thanks,
-- Marco