2015-08-18 12:21 GMT+03:00 Aneesh Kumar K.V [off-list ref]:

Andrey Ryabinin [off-list ref] writes:

quoted

2015-08-18 8:42 GMT+03:00 Aneesh Kumar K.V [off-list ref]:

quoted

Andrey Ryabinin [off-list ref] writes:


But that is introducting conditionals in core code for no real benefit.
This also will break when we eventually end up tracking vmalloc ?

Ok, that's a very good reason to not do this.

I see one potential problem in the way you use kasan_zero_page, though.
memset/memcpy of large portions of memory ( > 8 * PAGE_SIZE) will end up
in overflowing kasan_zero_page when we check shadow in memory_is_poisoned_n()

Any suggestion on how to fix that ? I guess we definitely don't want to

Wait, I was wrong, we should be fine.
In memory_is_poisoned_n():

ret = memory_is_zero(kasan_mem_to_shadow((void *)addr),
            kasan_mem_to_shadow((void *)addr + size - 1) + 1);

So this will be: memory_is_zero(kasan_zero_page, (char *)kasan_zero_page + 1);
Which means that we will access only 1 byte of kasan_zero_page.

check for addr and size in memset/memcpy. The other option is to
do zero page mapping as is done for other architectures. That is we map
via page table a zero page. But we still have the issue of memory we
need to map the entire vmalloc range (page table memory). I was hoping to
avoid all those complexities.


-aneesh