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Subject: Re: [PATCH v3] mm/kasan: dump alloc and free stack for page allocator
To:     Walter Wu <walter-zh.wu@mediatek.com>
Cc:     Qian Cai <cai@lca.pw>, Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Andrey Konovalov <andreyknvl@google.com>,
        Arnd Bergmann <arnd@arndb.de>, linux-kernel@vger.kernel.org,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com
References: <20190911083921.4158-1-walter-zh.wu@mediatek.com>
 <5E358F4B-552C-4542-9655-E01C7B754F14@lca.pw>
 <c4d2518f-4813-c941-6f47-73897f420517@suse.cz>
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From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <613f9f23-c7f0-871f-fe13-930c35ef3105@suse.cz>
Date:   Thu, 12 Sep 2019 16:31:42 +0200
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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?