Re: [RFC/PATCH v2 02/10] x86_64: add KASan support

[H. Peter Anvin]

On 09/10/2014 10:31 PM, Andrey Ryabinin wrote:
> On 09/11/2014 08:01 AM, H. Peter Anvin wrote:
>> On 09/10/2014 07:31 AM, Andrey Ryabinin wrote:
>>> This patch add arch specific code for kernel address sanitizer.
>>>
>>> 16TB of virtual addressed used for shadow memory.
>>> It's located in range [0xffff800000000000 - 0xffff900000000000]
>>> Therefore PAGE_OFFSET has to be changed from 0xffff880000000000
>>> to 0xffff900000000000.
>>
>> NAK on this.
>>
>> 0xffff880000000000 is the lowest usable address because we have agreed
>> to leave 0xffff800000000000-0xffff880000000000 for the hypervisor or
>> other non-OS uses.
>>
>> Bumping PAGE_OFFSET seems needlessly messy, why not just designate a
>> zone higher up in memory?
>>
> 
> I already answered to Dave why I choose to place shadow bellow PAGE_OFFSET (answer copied bellow).
> In short - yes, shadow could be higher. But for some sort of kernel bugs we could have confusing oopses in kasan kernel.
> 

Confusing how?  I presume you are talking about something trying to
touch a non-canonical address, which is usually a very blatant type of bug.

	-hpa


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