Re: [PATCH] x86/kasan: map shadow for percpu pages on demand

["Yin, Fengwei" <fengwei.yin@intel.com>]

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