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Message-ID: <7afa3099-cc62-b439-24ea-4d04f03ab402@intel.com>
Date:   Mon, 31 Oct 2022 08:15:40 +0800
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Subject: Re: [PATCH] x86/kasan: map shadow for percpu pages on demand
Content-Language: en-US
To:     Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "kernel test robot" <yujie.liu@intel.com>
CC:     Seth Jenkins <sethjenkins@google.com>,
        Kees Cook <keescook@chromium.org>,
        <linux-kernel@vger.kernel.org>, <x86@kernel.org>,
        Alexander Potapenko <glider@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        <kasan-dev@googlegroups.com>, Thomas Gleixner <tglx@linutronix.de>,
        "Ingo Molnar" <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, Andy Lutomirski <luto@kernel.org>
References: <864b4fbe-4462-9962-7afd-9140d5165cdb@intel.com>
 <20221027213105.4905-1-ryabinin.a.a@gmail.com>
 <3a372c25-7ce1-e931-8d7e-a2e14b82c8f0@intel.com>
 <c6fbc75a-4e8c-05f4-c1d9-53693a7c604f@gmail.com>
From:   "Yin, Fengwei" <fengwei.yin@intel.com>
In-Reply-To: <c6fbc75a-4e8c-05f4-c1d9-53693a7c604f@gmail.com>
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On 10/28/2022 10:20 PM, Andrey Ryabinin wrote:
> 
> 
> On 10/28/22 05:51, Yin, Fengwei wrote:
>> Hi Andrey,
>>
> 
>>>  void __init kasan_init(void)
>>>  {
>>>  	int i;
>>> @@ -393,9 +405,6 @@ void __init kasan_init(void)
>>>  		kasan_mem_to_shadow((void *)VMALLOC_END + 1),
>>>  		shadow_cpu_entry_begin);
>>>  
>>> -	kasan_populate_shadow((unsigned long)shadow_cpu_entry_begin,
>>> -			      (unsigned long)shadow_cpu_entry_end, 0);
>>> -
>> There will be address in the range (shadow_cpu_entry_begin, shadow_cpu_entry_end)
>> which has no KASAN shadow mapping populated after the patch. Not sure whether
>> it could be a problem. Thanks.
>>
> 
> 
> This shouldn't be a problem. It's vital to have shadow *only* for addresses with mapped memory.
> Shadow address accessed only if the address itself accessed. So the difference between not having shadow
> for address with no mapping vs having it, is whether we crash on access to KASAN shadow or crash few
> instructions later on access to the address itself.

Thanks for clarification.

Regards
Yin, Fengwei