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Message-ID: <1567607063.32522.24.camel@mtksdccf07>
Subject: Re: [PATCH 1/2] mm/kasan: dump alloc/free stack for page allocator
From:   Walter Wu <walter-zh.wu@mediatek.com>
To:     Vlastimil Babka <vbabka@suse.cz>
CC:     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>,
        Arnd Bergmann <arnd@arndb.de>, <kasan-dev@googlegroups.com>,
        <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-mediatek@lists.infradead.org>, <wsd_upstream@mediatek.com>
Date:   Wed, 4 Sep 2019 22:24:23 +0800
In-Reply-To: <7998e8f1-e5e2-da84-ea1f-33e696015dce@suse.cz>
References: <20190904065133.20268-1-walter-zh.wu@mediatek.com>
         <401064ae-279d-bef3-a8d5-0fe155d0886d@suse.cz>
         <1567605965.32522.14.camel@mtksdccf07>
         <7998e8f1-e5e2-da84-ea1f-33e696015dce@suse.cz>
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On Wed, 2019-09-04 at 16:13 +0200, Vlastimil Babka wrote:
> On 9/4/19 4:06 PM, Walter Wu wrote:
> > On Wed, 2019-09-04 at 14:49 +0200, Vlastimil Babka wrote:
> >> On 9/4/19 8:51 AM, Walter Wu wrote:
> >> > This patch is KASAN report adds the alloc/free stacks for page allocator
> >> > in order to help programmer to see memory corruption caused by page.
> >> > 
> >> > By default, KASAN doesn't record alloc/free stack for page allocator.
> >> > It is difficult to fix up page use-after-free issue.
> >> > 
> >> > This feature depends on page owner to record the last stack of pages.
> >> > It is very helpful for solving the page use-after-free or out-of-bound.
> >> > 
> >> > KASAN report will show the last stack of page, it may be:
> >> > a) If page is in-use state, then it prints alloc stack.
> >> >    It is useful to fix up page out-of-bound issue.
> >> 
> >> I expect this will conflict both in syntax and semantics with my series [1] that
> >> adds the freeing stack to page_owner when used together with debug_pagealloc,
> >> and it's now in mmotm. Glad others see the need as well :) Perhaps you could
> >> review the series, see if it fulfils your usecase (AFAICS the series should be a
> >> superset, by storing both stacks at once), and perhaps either make KASAN enable
> >> debug_pagealloc, or turn KASAN into an alternative enabler of the functionality
> >> there?
> >> 
> >> Thanks, Vlastimil
> >> 
> >> [1] https://lore.kernel.org/linux-mm/20190820131828.22684-1-vbabka@suse.cz/t/#u
> >> 
> > Thanks your information.
> > We focus on the smartphone, so it doesn't enable
> > CONFIG_TRANSPARENT_HUGEPAGE, Is it invalid for our usecase?
> 
> The THP fix is not required for the rest of the series, it was even merged to
> mainline separately.
> 
> > And It looks like something is different, because we only need last
> > stack of page, so it can decrease memory overhead.
> 
> That would save you depot_stack_handle_t (which is u32) per page. I guess that's
> nothing compared to KASAN overhead?
> 
If we can use less memory, we can achieve what we want. Why not?

Thanks.
Walter