Subject: Re: [PATCH v8 1/5] kasan: support backing vmalloc space with real shadow memory

From: Daniel Axtens <[email-masked]>
Date: Tue, 15 Oct 2019 17:29:40 +1100

>>> @@ -2497,6 +2533,9 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
>>>  	if (!addr)
>>>  		return NULL;
>>>  
>>> +	if (kasan_populate_vmalloc(real_size, area))
>>> +		return NULL;
>>> +
>>
>> KASAN itself uses __vmalloc_node_range() to allocate and map shadow in memory online callback.
>> So we should either skip non-vmalloc and non-module addresses here or teach kasan's memory online/offline
>> callbacks to not use __vmalloc_node_range() (do something similar to kasan_populate_vmalloc() perhaps?). 
>
> Ah, right you are. I haven't been testing that.
>
> I am a bit nervous about further restricting kasan_populate_vmalloc: I
> seem to remember having problems with code using the vmalloc family of
> functions to map memory that doesn't lie within vmalloc space but which
> still has instrumented accesses.

I was wrong or remembering early implementation bugs.

If the memory we're allocating in __vmalloc_node_range falls outside of
vmalloc and module space, it shouldn't be getting shadow mapped for it
by kasan_populate_vmalloc. For v9, I've guarded the call with
is_vmalloc_or_module. It seems to work fine when tested with hotplugged
memory.

Thanks again.

Regards,
Daniel

> On the other hand, I'm not keen on rewriting any of the memory
> on/offline code if I can avoid it!
>
> I'll have a look and get back you as soon as I can.
>
> Thanks for catching this.
>
> Kind regards,
> Daniel
>
>>
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