From: Andrey Ryabinin <aryabinin@virtuozzo.com>
To: Walter Wu <walter-zh.wu@mediatek.com>
Cc: Dmitry Vyukov <dvyukov@google.com>,
Alexander Potapenko <glider@google.com>,
Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Arnd Bergmann <arnd@arndb.de>, Vasily Gorbik <gor@linux.ibm.com>,
Andrey Konovalov <andreyknvl@google.com>,
"Jason A . Donenfeld" <Jason@zx2c4.com>,
Miles Chen <miles.chen@mediatek.com>,
kasan-dev <kasan-dev@googlegroups.com>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
linux-mediatek@lists.infradead.org,
wsd_upstream <wsd_upstream@mediatek.com>
Subject: Re: [PATCH v3] kasan: add memory corruption identification for software tag-based mode
Date: Fri, 26 Jul 2019 15:00:00 +0300 [thread overview]
Message-ID: <e62da62a-2a63-3a1c-faeb-9c5561a5170c@virtuozzo.com> (raw)
In-Reply-To: <1563789162.31223.3.camel@mtksdccf07>
On 7/22/19 12:52 PM, Walter Wu wrote:
> On Thu, 2019-07-18 at 19:11 +0300, Andrey Ryabinin wrote:
>>
>> On 7/15/19 6:06 AM, Walter Wu wrote:
>>> On Fri, 2019-07-12 at 13:52 +0300, Andrey Ryabinin wrote:
>>>>
>>>> On 7/11/19 1:06 PM, Walter Wu wrote:
>>>>> On Wed, 2019-07-10 at 21:24 +0300, Andrey Ryabinin wrote:
>>>>>>
>>>>>> On 7/9/19 5:53 AM, Walter Wu wrote:
>>>>>>> On Mon, 2019-07-08 at 19:33 +0300, Andrey Ryabinin wrote:
>>>>>>>>
>>>>>>>> On 7/5/19 4:34 PM, Dmitry Vyukov wrote:
>>>>>>>>> On Mon, Jul 1, 2019 at 11:56 AM Walter Wu <walter-zh.wu@mediatek.com> wrote:
>>>>>>
>>>>>>>>>
>>>>>>>>> Sorry for delays. I am overwhelm by some urgent work. I afraid to
>>>>>>>>> promise any dates because the next week I am on a conference, then
>>>>>>>>> again a backlog and an intern starting...
>>>>>>>>>
>>>>>>>>> Andrey, do you still have concerns re this patch? This change allows
>>>>>>>>> to print the free stack.
>>>>>>>>
>>>>>>>> I 'm not sure that quarantine is a best way to do that. Quarantine is made to delay freeing, but we don't that here.
>>>>>>>> If we want to remember more free stacks wouldn't be easier simply to remember more stacks in object itself?
>>>>>>>> Same for previously used tags for better use-after-free identification.
>>>>>>>>
>>>>>>>
>>>>>>> Hi Andrey,
>>>>>>>
>>>>>>> We ever tried to use object itself to determine use-after-free
>>>>>>> identification, but tag-based KASAN immediately released the pointer
>>>>>>> after call kfree(), the original object will be used by another
>>>>>>> pointer, if we use object itself to determine use-after-free issue, then
>>>>>>> it has many false negative cases. so we create a lite quarantine(ring
>>>>>>> buffers) to record recent free stacks in order to avoid those false
>>>>>>> negative situations.
>>>>>>
>>>>>> I'm telling that *more* than one free stack and also tags per object can be stored.
>>>>>> If object reused we would still have information about n-last usages of the object.
>>>>>> It seems like much easier and more efficient solution than patch you proposing.
>>>>>>
>>>>> To make the object reused, we must ensure that no other pointers uses it
>>>>> after kfree() release the pointer.
>>>>> Scenario:
>>>>> 1). The object reused information is valid when no another pointer uses
>>>>> it.
>>>>> 2). The object reused information is invalid when another pointer uses
>>>>> it.
>>>>> Do you mean that the object reused is scenario 1) ?
>>>>> If yes, maybe we can change the calling quarantine_put() location. It
>>>>> will be fully use that quarantine, but at scenario 2) it looks like to
>>>>> need this patch.
>>>>> If no, maybe i miss your meaning, would you tell me how to use invalid
>>>>> object information? or?
>>>>>
>>>>
>>>>
>>>> KASAN keeps information about object with the object, right after payload in the kasan_alloc_meta struct.
>>>> This information is always valid as long as slab page allocated. Currently it keeps only one last free stacktrace.
>>>> It could be extended to record more free stacktraces and also record previously used tags which will allow you
>>>> to identify use-after-free and extract right free stacktrace.
>>>
>>> Thanks for your explanation.
>>>
>>> For extend slub object, if one record is 9B (sizeof(u8)+ sizeof(struct
>>> kasan_track)) and add five records into slub object, every slub object
>>> may add 45B usage after the system runs longer.
>>> Slub object number is easy more than 1,000,000(maybe it may be more
>>> bigger), then the extending object memory usage should be 45MB, and
>>> unfortunately it is no limit. The memory usage is more bigger than our
>>> patch.
>>
>> No, it's not necessarily more.
>> And there are other aspects to consider such as performance, how simple reliable the code is.
>>
>>>
>>> We hope tag-based KASAN advantage is smaller memory usage. If it’s
>>> possible, we should spend less memory in order to identify
>>> use-after-free. Would you accept our patch after fine tune it?
>>
>> Sure, if you manage to fix issues and demonstrate that performance penalty of your
>> patch is close to zero.
>
>
> I remember that there are already the lists which you concern. Maybe we
> can try to solve those problems one by one.
>
> 1. deadlock issue? cause by kmalloc() after kfree()?
smp_call_on_cpu()
> 2. decrease allocation fail, to modify GFP_NOWAIT flag to GFP_KERNEL?
No, this is not gonna work. Ideally we shouldn't have any allocations there.
It's not reliable and it hurts performance.
> 3. check whether slim 48 bytes (sizeof (qlist_object) +
> sizeof(kasan_alloc_meta)) and additional unique stacktrace in
> stackdepot?
> 4. duplicate struct 'kasan_track' information in two different places
>
Yup.
> Would you have any other concern? or?
>
It would be nice to see some performance numbers. Something that uses slab allocations a lot, e.g. netperf STREAM_STREAM test.
next prev parent reply other threads:[~2019-07-26 12:00 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-13 8:13 [PATCH v3] kasan: add memory corruption identification for software tag-based mode Walter Wu
2019-06-13 12:27 ` Andrey Ryabinin
2019-06-13 13:05 ` Dmitry Vyukov
2019-06-13 15:50 ` Andrey Ryabinin
2019-06-13 17:46 ` Walter Wu
2019-06-14 2:32 ` Walter Wu
2019-06-17 4:00 ` Walter Wu
2019-06-17 11:57 ` Dmitry Vyukov
2019-06-17 12:32 ` Walter Wu
2019-07-01 9:56 ` Walter Wu
2019-07-05 13:34 ` Dmitry Vyukov
2019-07-08 16:33 ` Andrey Ryabinin
2019-07-09 2:53 ` Walter Wu
2019-07-10 18:24 ` Andrey Ryabinin
2019-07-11 10:06 ` Walter Wu
2019-07-12 10:52 ` Andrey Ryabinin
2019-07-15 3:06 ` Walter Wu
2019-07-18 16:11 ` Andrey Ryabinin
2019-07-22 9:52 ` Walter Wu
2019-07-26 12:00 ` Andrey Ryabinin [this message]
2019-07-26 12:28 ` Walter Wu
2019-07-26 12:52 ` Andrey Ryabinin
2019-07-26 13:19 ` Walter Wu
2019-07-31 17:04 ` Andrey Ryabinin
2019-08-02 3:04 ` Walter Wu
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