Re: [RFC PATCH v2 13/15] khwasan: add hooks implementation

From: Andrey Konovalov <andreyknvl@google.com>
To: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>,
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Subject: Re: [RFC PATCH v2 13/15] khwasan: add hooks implementation
Date: Thu, 12 Apr 2018 19:37:27 +0200	[thread overview]
Message-ID: <CAAeHK+w1f4QSuan4onv-2ZxxSsi-ZYsdPOSuJ4=2ygJ2=q=VmA@mail.gmail.com> (raw)
In-Reply-To: <a29d22c7-bcae-ec8d-1810-95eef013e699@virtuozzo.com>

On Thu, Apr 12, 2018 at 7:20 PM, Andrey Ryabinin
<aryabinin@virtuozzo.com> wrote:
>> 1. Tag memory with a random tag in kasan_alloc_pages() and returned a
>> tagged pointer from pagealloc.
>
> Tag memory with a random tag in kasan_alloc_pages() and store that tag in page struct (that part is also in kasan_alloc_pages()).
> page_address(page) will retrieve that tag from struct page to return tagged address.
>
> I've no idea what do you mean by "returning a tagged pointer from pagealloc".
> Once again, the page allocator (__alloc_pages_nodemask()) returns pointer to *struct page*,
> not the address in the linear mapping where is that page mapped (or not mapped at all if this is highmem).
> One have to call page_address()/kmap() to use that page.

Ah, that's what I've been missing.

OK, I'll do that.

Thanks!

>
>
>> 2. Restore the tag for the pointers returned from page_address for
>> !PageSlab() pages.
>>
>
> Right.
>
>> 3. Set the tag to 0xff for the pointers returned from page_address for
>> PageSlab() pages.
>>
>
> Right.
>
>> Is this correct?
>>
>> In 2 instead of storing the tag in page_struct, we can just recover it
>> from the shadow memory that corresponds to that page. What do you
>> think about this?
>
> Sounds ok. Don't see any problem with that.
>
>