linux-kernel - Re: [PATCH v3 1/5] arm64: kasan: don't populate vmalloc area for CONFIG_KASAN

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Message-ID: <20210319173758.GC6832@arm.com>
Date:   Fri, 19 Mar 2021 17:37:58 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Lecopzer Chen <lecopzer.chen@...iatek.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kasan-dev@...glegroups.com, linux-arm-kernel@...ts.infradead.org,
        will@...nel.org, dan.j.williams@...el.com, aryabinin@...tuozzo.com,
        glider@...gle.com, dvyukov@...gle.com, akpm@...ux-foundation.org,
        linux-mediatek@...ts.infradead.org, yj.chiang@...iatek.com,
        ardb@...nel.org, andreyknvl@...gle.com, broonie@...nel.org,
        linux@...ck-us.net, rppt@...nel.org, tyhicks@...ux.microsoft.com,
        robin.murphy@....com, vincenzo.frascino@....com,
        gustavoars@...nel.org, lecopzer@...il.com
Subject: Re: [PATCH v3 1/5] arm64: kasan: don't populate vmalloc area for
 CONFIG_KASAN_VMALLOC

On Sat, Feb 06, 2021 at 04:35:48PM +0800, Lecopzer Chen wrote:
> Linux support KAsan for VMALLOC since commit 3c5c3cfb9ef4da9
> ("kasan: support backing vmalloc space with real shadow memory")
> 
> Like how the MODULES_VADDR does now, just not to early populate
> the VMALLOC_START between VMALLOC_END.
> 
> Before:
> 
> MODULE_VADDR: no mapping, no zoreo shadow at init
> VMALLOC_VADDR: backed with zero shadow at init
> 
> After:
> 
> MODULE_VADDR: no mapping, no zoreo shadow at init
> VMALLOC_VADDR: no mapping, no zoreo shadow at init

s/zoreo/zero/

> Thus the mapping will get allocated on demand by the core function
> of KASAN_VMALLOC.
> 
>   -----------  vmalloc_shadow_start
>  |           |
>  |           |
>  |           | <= non-mapping
>  |           |
>  |           |
>  |-----------|
>  |///////////|<- kimage shadow with page table mapping.
>  |-----------|
>  |           |
>  |           | <= non-mapping
>  |           |
>  ------------- vmalloc_shadow_end
>  |00000000000|
>  |00000000000| <= Zero shadow
>  |00000000000|
>  ------------- KASAN_SHADOW_END
> 
> Signed-off-by: Lecopzer Chen <lecopzer.chen@...iatek.com>
> ---
>  arch/arm64/mm/kasan_init.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
> index d8e66c78440e..20d06008785f 100644
> --- a/arch/arm64/mm/kasan_init.c
> +++ b/arch/arm64/mm/kasan_init.c
> @@ -214,6 +214,7 @@ static void __init kasan_init_shadow(void)
>  {
>  	u64 kimg_shadow_start, kimg_shadow_end;
>  	u64 mod_shadow_start, mod_shadow_end;
> +	u64 vmalloc_shadow_end;
>  	phys_addr_t pa_start, pa_end;
>  	u64 i;
>  
> @@ -223,6 +224,8 @@ static void __init kasan_init_shadow(void)
>  	mod_shadow_start = (u64)kasan_mem_to_shadow((void *)MODULES_VADDR);
>  	mod_shadow_end = (u64)kasan_mem_to_shadow((void *)MODULES_END);
>  
> +	vmalloc_shadow_end = (u64)kasan_mem_to_shadow((void *)VMALLOC_END);
> +
>  	/*
>  	 * We are going to perform proper setup of shadow memory.
>  	 * At first we should unmap early shadow (clear_pgds() call below).
> @@ -241,12 +244,17 @@ static void __init kasan_init_shadow(void)
>  
>  	kasan_populate_early_shadow(kasan_mem_to_shadow((void *)PAGE_END),
>  				   (void *)mod_shadow_start);
> -	kasan_populate_early_shadow((void *)kimg_shadow_end,
> -				   (void *)KASAN_SHADOW_END);
>  
> -	if (kimg_shadow_start > mod_shadow_end)
> -		kasan_populate_early_shadow((void *)mod_shadow_end,
> -					    (void *)kimg_shadow_start);

Not something introduced by this patch but what happens if this
condition is false? It means that kimg_shadow_end < mod_shadow_start and
the above kasan_populate_early_shadow(PAGE_END, mod_shadow_start)
overlaps with the earlier kasan_map_populate(kimg_shadow_start,
kimg_shadow_end).

> +	if (IS_ENABLED(CONFIG_KASAN_VMALLOC))
> +		kasan_populate_early_shadow((void *)vmalloc_shadow_end,
> +					    (void *)KASAN_SHADOW_END);
> +	else {
> +		kasan_populate_early_shadow((void *)kimg_shadow_end,
> +					    (void *)KASAN_SHADOW_END);
> +		if (kimg_shadow_start > mod_shadow_end)
> +			kasan_populate_early_shadow((void *)mod_shadow_end,
> +						    (void *)kimg_shadow_start);
> +	}
>  
>  	for_each_mem_range(i, &pa_start, &pa_end) {
>  		void *start = (void *)__phys_to_virt(pa_start);
> -- 
> 2.25.1
> 

-- 
Catalin