Re: [PATCH v3] mm/kasan: dump alloc and free stack for page allocator

Vlastimil Babka
2019-09-12T14:31:46Z

On 9/12/19 4:08 PM, Walter Wu wrote:
>
>> extern void __reset_page_owner(struct page *page, unsigned int order);
>> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
>> index 6c9682ce0254..dc560c7562e8 100644
>> --- a/lib/Kconfig.kasan
>> +++ b/lib/Kconfig.kasan
>> @@ -41,6 +41,8 @@ config KASAN_GENERIC
>> select SLUB_DEBUG if SLUB
>> select CONSTRUCTORS
>> select STACKDEPOT
>> + select PAGE_OWNER
>> + select PAGE_OWNER_FREE_STACK
>> help
>> Enables generic KASAN mode.
>> Supported in both GCC and Clang. With GCC it requires version 4.9.2
>> @@ -63,6 +65,8 @@ config KASAN_SW_TAGS
>> select SLUB_DEBUG if SLUB
>> select CONSTRUCTORS
>> select STACKDEPOT
>> + select PAGE_OWNER
>> + select PAGE_OWNER_FREE_STACK
>> help
>
> What is the difference between PAGE_OWNER+PAGE_OWNER_FREE_STACK and
> DEBUG_PAGEALLOC?

Same memory usage, but debug_pagealloc means also extra checks and
restricting memory access to freed pages to catch UAF.

> If you directly enable PAGE_OWNER+PAGE_OWNER_FREE_STACK
> PAGE_OWNER_FREE_STACK,don't you think low-memory device to want to use
> KASAN?

OK, so it should be optional? But I think it's enough to distinguish no
PAGE_OWNER at all, and PAGE_OWNER+PAGE_OWNER_FREE_STACK together - I
don't see much point in PAGE_OWNER only for this kind of debugging.

So how about this? KASAN wouldn't select PAGE_OWNER* but it would be
recommended in the help+docs. When PAGE_OWNER and KASAN are selected by
user, PAGE_OWNER_FREE_STACK gets also selected, and both will be also
runtime enabled without explicit page_owner=on.
I mostly want to avoid another boot-time option for enabling
PAGE_OWNER_FREE_STACK.
Would that be enough flexibility for low-memory devices vs full-fledged
debugging?