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Date: Thu, 10 Jul 2014 23:48:45 +0400
Message-ID: <CAPAsAGwYZ9AVUoOMipZEe8jdmJfd=aULR+yoVH5FqzW1Qa75AQ@mail.gmail.com>
Subject: Re: [RFC/PATCH RESEND -next 01/21] Add kernel address sanitizer infrastructure.
From: Andrey Ryabinin <ryabinin.a.a@gmail.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Andrey Ryabinin <a.ryabinin@samsung.com>, linux-kernel@vger.kernel.org,
        Dmitry Vyukov <dvyukov@google.com>,
        Konstantin Serebryany <kcc@google.com>,
        Alexey Preobrazhensky <preobr@google.com>,
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        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
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        Andrew Morton <akpm@linux-foundation.org>,
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2014-07-10 19:55 GMT+04:00 Dave Hansen <dave.hansen@intel.com>:
> On 07/10/2014 05:12 AM, Andrey Ryabinin wrote:
>> On 07/10/14 00:26, Dave Hansen wrote:
>>> On 07/09/2014 04:29 AM, Andrey Ryabinin wrote:
>>>> Address sanitizer dedicates 1/8 of the low memory to the shadow memory and uses direct
>>>> mapping with a scale and offset to translate a memory address to its corresponding
>>>> shadow address.
>>>>
>>>> Here is function to translate address to corresponding shadow address:
>>>>
>>>>      unsigned long kasan_mem_to_shadow(unsigned long addr)
>>>>      {
>>>>                 return ((addr - PAGE_OFFSET) >> KASAN_SHADOW_SCALE_SHIFT)
>>>>                              + kasan_shadow_start;
>>>>      }
>>>
>>> How does this interact with vmalloc() addresses or those from a kmap()?
>>>
>> It's used only for lowmem:
>>
>> static inline bool addr_is_in_mem(unsigned long addr)
>> {
>>       return likely(addr >= PAGE_OFFSET && addr < (unsigned long)high_memory);
>> }
>
> That's fine, and definitely covers the common cases.  Could you make
> sure to call this out explicitly?  Also, there's nothing to _keep_ this
> approach working for things out of the direct map, right?  It would just
> be a matter of updating the shadow memory to have entries for the other
> virtual address ranges.

Why do you want shadow for things out of the direct map?
If you want to catch use-after-free in vmalloc than DEBUG_PAGEALLOC
will be enough.
If you want catch out-of-bounds in vmalloc you don't need anything,
because vmalloc
allocates guarding hole in the end.
Or do you want something else?

>
> addr_is_in_mem() is a pretty bad name for what it's doing. :)
>
> I'd probably call it something like kasan_tracks_vaddr().
>
Agree

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-- 
Best regards,
Andrey Ryabinin
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