Date:	Tue, 17 May 2016 10:55:13 +0200
From:	Alexander Potapenko <glider@...gle.com>
To:	Alexey Klimov <klimov.linux@...il.com>
Cc:	Andrey Konovalov <adech.fo@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Joonsoo Kim <js1304@...il.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	kasan-dev <kasan-dev@...glegroups.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9] mm: kasan: Initial memory quarantine implementation

Hello Alexey,

On Tue, May 17, 2016 at 12:03 AM, Alexey Klimov <klimov.linux@...il.com> wrote:
> Hi Alexander,
>
> On Wed, May 11, 2016 at 6:18 PM, Alexander Potapenko <glider@...gle.com> wrote:
>> Quarantine isolates freed objects in a separate queue. The objects are
>> returned to the allocator later, which helps to detect use-after-free
>> errors.
>>
>> Freed objects are first added to per-cpu quarantine queues.
>> When a cache is destroyed or memory shrinking is requested, the objects
>> are moved into the global quarantine queue. Whenever a kmalloc call
>> allows memory reclaiming, the oldest objects are popped out of the
>> global queue until the total size of objects in quarantine is less than
>> 3/4 of the maximum quarantine size (which is a fraction of installed
>> physical memory).
>>
>> As long as an object remains in the quarantine, KASAN is able to report
>> accesses to it, so the chance of reporting a use-after-free is increased.
>> Once the object leaves quarantine, the allocator may reuse it, in which
>> case the object is unpoisoned and KASAN can't detect incorrect accesses
>> to it.
>>
>> Right now quarantine support is only enabled in SLAB allocator.
>> Unification of KASAN features in SLAB and SLUB will be done later.
>>
>> This patch is based on the "mm: kasan: quarantine" patch originally
>> prepared by Dmitry Chernenkov. A number of improvements have been
>> suggested by Andrey Ryabinin.
>>
>> Signed-off-by: Alexander Potapenko <glider@...gle.com>
>> ---
>> v2: - added copyright comments
>>     - per request from Joonsoo Kim made __cache_free() more straightforward
>>     - added comments for smp_load_acquire()/smp_store_release()
>>
>> v3: - incorporate changes introduced by the "mm, kasan: SLAB support" patch
>>
>> v4: - fix kbuild compile-time error (missing ___cache_free() declaration)
>>       and a warning (wrong format specifier)
>>
>> v6: - extended the patch description
>>     - dropped the unused qlist_remove() function
>>
>> v9: - incorporate the fixes by Andrey Ryabinin:
>>       * Fix comment styles,
>>       * Get rid of some ifdefs
>>       * Revert needless functions renames in quarantine patch
>>       * Remove needless local_irq_save()/restore() in
>>         per_cpu_remove_cache()
>>       * Add new 'struct qlist_node' instead of 'void **' types. This makes
>>         code a bit more redable.
>>     - remove the non-deterministic quarantine test
>>     - dropped smp_load_acquire()/smp_store_release()
>> ---
>>  include/linux/kasan.h |  13 ++-
>>  mm/kasan/Makefile     |   1 +
>>  mm/kasan/kasan.c      |  57 ++++++++--
>>  mm/kasan/kasan.h      |  21 +++-
>>  mm/kasan/quarantine.c | 291 ++++++++++++++++++++++++++++++++++++++++++++++++++
>>  mm/kasan/report.c     |   1 +
>>  mm/mempool.c          |   2 +-
>>  mm/slab.c             |  12 ++-
>>  mm/slab.h             |   2 +
>>  mm/slab_common.c      |   2 +
>>  10 files changed, 387 insertions(+), 15 deletions(-)
>>  create mode 100644 mm/kasan/quarantine.c
>>
>> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
>> index 737371b..611927f 100644
>> --- a/include/linux/kasan.h
>> +++ b/include/linux/kasan.h
>> @@ -50,6 +50,8 @@ void kasan_free_pages(struct page *page, unsigned int order);
>>
>
> [...]
>
>> diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
>> new file mode 100644
>> index 0000000..4973505
>> --- /dev/null
>> +++ b/mm/kasan/quarantine.c
>> @@ -0,0 +1,291 @@
>> +/*
>> + * KASAN quarantine.
>> + *
>> + * Author: Alexander Potapenko <glider@...gle.com>
>> + * Copyright (C) 2016 Google, Inc.
>> + *
>> + * Based on code by Dmitry Chernenkov.
>> + *
>> + * This program is free software; you can redistribute it and/or
>> + * modify it under the terms of the GNU General Public License
>> + * version 2 as published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope that it will be useful, but
>> + * WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> + * General Public License for more details.
>> + *
>> + */
>> +
>> +#include <linux/gfp.h>
>> +#include <linux/hash.h>
>> +#include <linux/kernel.h>
>> +#include <linux/mm.h>
>> +#include <linux/percpu.h>
>> +#include <linux/printk.h>
>> +#include <linux/shrinker.h>
>> +#include <linux/slab.h>
>> +#include <linux/string.h>
>> +#include <linux/types.h>
>> +
>> +#include "../slab.h"
>> +#include "kasan.h"
>> +
>> +/* Data structure and operations for quarantine queues. */
>> +
>> +/*
>> + * Each queue is a signle-linked list, which also stores the total size of
>> + * objects inside of it.
>> + */
>> +struct qlist_head {
>> +       struct qlist_node *head;
>> +       struct qlist_node *tail;
>> +       size_t bytes;
>> +};
>> +
>> +#define QLIST_INIT { NULL, NULL, 0 }
>> +
>> +static bool qlist_empty(struct qlist_head *q)
>> +{
>> +       return !q->head;
>> +}
>> +
>> +static void qlist_init(struct qlist_head *q)
>> +{
>> +       q->head = q->tail = NULL;
>> +       q->bytes = 0;
>> +}
>> +
>> +static void qlist_put(struct qlist_head *q, struct qlist_node *qlink,
>> +               size_t size)
>> +{
>> +       if (unlikely(qlist_empty(q)))
>> +               q->head = qlink;
>> +       else
>> +               q->tail->next = qlink;
>> +       q->tail = qlink;
>> +       qlink->next = NULL;
>> +       q->bytes += size;
>> +}
>> +
>> +static void qlist_move_all(struct qlist_head *from, struct qlist_head *to)
>> +{
>> +       if (unlikely(qlist_empty(from)))
>> +               return;
>> +
>> +       if (qlist_empty(to)) {
>> +               *to = *from;
>> +               qlist_init(from);
>> +               return;
>> +       }
>> +
>> +       to->tail->next = from->head;
>> +       to->tail = from->tail;
>> +       to->bytes += from->bytes;
>> +
>> +       qlist_init(from);
>> +}
>> +
>> +static void qlist_move(struct qlist_head *from, struct qlist_node *last,
>> +               struct qlist_head *to, size_t size)
>> +{
>> +       if (unlikely(last == from->tail)) {
>> +               qlist_move_all(from, to);
>> +               return;
>> +       }
>> +       if (qlist_empty(to))
>> +               to->head = from->head;
>> +       else
>> +               to->tail->next = from->head;
>> +       to->tail = last;
>> +       from->head = last->next;
>> +       last->next = NULL;
>> +       from->bytes -= size;
>> +       to->bytes += size;
>> +}
>
> I see conversation with Andrew in previous emails about moving this
> code above into generic library facility but I don't anything is going
> on here. I also feel like this belongs to lib/*.
> Do I miss something or did you decide to do it later?
>
> [...]
I remember Andrew said that, but I think it will be cleaner to make
that change in a separate patch.
> --
> Best regards, Klimov Alexey



-- 
Alexander Potapenko
Software Engineer

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