Re: [RFC/PATCH RESEND -next 01/21] Add kernel address sanitizer infrastructure.

From: Andrey Ryabinin
Date: Thu Jul 10 2014 - 15:48:51 EST

2014-07-10 19:55 GMT+04:00 Dave Hansen <dave.hansen@xxxxxxxxx>:
> 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().

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Best regards,
Andrey Ryabinin
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