linux-kernel - Re: [PATCH v4 5/7] mm, kasan: Stackdepot implementation. Enable stackdepot for SLAB

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAG_fn=Xg7=vvPet8xcNiLZde_Y98OMuH-DjCgvrcxn7eMaARYQ@mail.gmail.com>
Date:	Fri, 11 Mar 2016 15:49:55 +0100
From:	Alexander Potapenko <glider@...gle.com>
To:	Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Andrey Konovalov <adech.fo@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	JoonSoo Kim <js1304@...il.com>,
	Kostya Serebryany <kcc@...gle.com>,
	kasan-dev <kasan-dev@...glegroups.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH v4 5/7] mm, kasan: Stackdepot implementation. Enable
 stackdepot for SLAB

On Fri, Mar 11, 2016 at 12:43 PM, Andrey Ryabinin
<ryabinin.a.a@...il.com> wrote:
>
>
> On 03/11/2016 02:18 PM, Alexander Potapenko wrote:
>> On Thu, Mar 10, 2016 at 5:58 PM, Andrey Ryabinin <ryabinin.a.a@...il.com> wrote:
>>> 2016-03-08 14:42 GMT+03:00 Alexander Potapenko <glider@...gle.com>:
>>>> On Tue, Mar 1, 2016 at 12:57 PM, Andrey Ryabinin <ryabinin.a.a@...il.com> wrote:
>>>>>>>
>>>>>>>> +                     page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER);
>>>>>>>
>>>>>>> STACK_ALLOC_ORDER = 4 - that's a lot. Do you really need that much?
>>>>>>
>>>>>> Part of the issue the atomic context above. When we can't allocate
>>>>>> memory we still want to save the stack trace. When we have less than
>>>>>> STACK_ALLOC_ORDER memory, we try to preallocate another
>>>>>> STACK_ALLOC_ORDER in advance. So in the worst case, we have
>>>>>> STACK_ALLOC_ORDER memory and that should be enough to handle all
>>>>>> kmalloc/kfree in the atomic context. 1 page does not look enough. I
>>>>>> think Alex did some measuring of the failure race (when we are out of
>>>>>> memory and can't allocate more).
>>>>>>
>>>>>
>>>>> A lot of 4-order pages will lead to high fragmentation. You don't need physically contiguous memory here,
>>>>> so try to use vmalloc(). It is slower, but fragmentation won't be problem.
>>>> I've tried using vmalloc(), but turned out it's calling KASAN hooks
>>>> again. Dealing with reentrancy in this case sounds like an overkill.
>>>
>>> We'll have to deal with recursion eventually. Using stackdepot for
>>> page owner will cause recursion.
>>>
>>>> Given that we only require 9 Mb most of the time, is allocating
>>>> physical pages still a problem?
>>>>
>>>
>>> This is not about size, this about fragmentation. vmalloc allows to
>>> utilize available low-order pages,
>>> hence reduce the fragmentation.
>> I've attempted to add __vmalloc(STACK_ALLOC_SIZE, alloc_flags,
>> PAGE_KERNEL) (also tried vmalloc(STACK_ALLOC_SIZE)) instead of
>> page_alloc() and am now getting a crash in
>> kmem_cache_alloc_node_trace() in mm/slab.c, because it doesn't allow
>> the kmem_cache pointer to be NULL (it's dereferenced when calling
>> trace_kmalloc_node()).
>>
>> Steven, do you know if this because of my code violating some contract
>> (e.g. I'm calling vmalloc() too early, when kmalloc_caches[] haven't
>> been initialized),
>
> Probably. kmem_cache_init() goes before vmalloc_init().
The solution I'm currently testing is to introduce a per-CPU recursion
flag that depot_save_stack() checks and bails out if it's set.
In addition I look at |kmalloc_caches[KMALLOC_SHIFT_HIGH]| and
in_interrupt() to see if vmalloc() is available.
In the case it is not, I fall back to alloc_pages().

Right now (after 20 minutes of running Trinity) vmalloc() has been
called 490 times, alloc_pages() - only 13 times.
I hope it's now much better from the fragmentation point of view.
>
>> or is this a bug in kmem_cache_alloc_node_trace()
>> itself?
>>



-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg