On 07/10/2014 12:48 PM, Andrey Ryabinin wrote:
>>>> 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?
That's all true for page-size accesses. Address sanitizer's biggest
advantage over using the page tables is that it can do checks at
sub-page granularity. But, we don't have any APIs that I can think of
that _care_ about <PAGE_SIZE outside of the direct map (maybe zsmalloc,
but that's pretty obscure).
So I guess it doesn't matter.
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