From: Walter Wu <walter-zh.wu@mediatek.com>
To: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: wsd_upstream@mediatek.com,
"Jason A . Donenfeld" <Jason@zx2c4.com>,
Vasily Gorbik <gor@linux.ibm.com>, Arnd Bergmann <arnd@arndb.de>,
linux-mm@kvack.org, Andrey Konovalov <andreyknvl@google.com>,
linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
Pekka Enberg <penberg@kernel.org>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Miles Chen <miles.chen@mediatek.com>,
Alexander Potapenko <glider@google.com>,
linux-arm-kernel@lists.infradead.org,
David Rientjes <rientjes@google.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
linux-mediatek@lists.infradead.org,
Christoph Lameter <cl@linux.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Dmitry Vyukov <dvyukov@google.com>
Subject: Re: [PATCH v3] kasan: add memory corruption identification for software tag-based mode
Date: Fri, 14 Jun 2019 01:46:39 +0800 [thread overview]
Message-ID: <1560447999.15814.15.camel@mtksdccf07> (raw)
In-Reply-To: <da7591c9-660d-d380-d59e-6d70b39eaa6b@virtuozzo.com>
On Thu, 2019-06-13 at 15:27 +0300, Andrey Ryabinin wrote:
>
> On 6/13/19 11:13 AM, Walter Wu wrote:
> > This patch adds memory corruption identification at bug report for
> > software tag-based mode, the report show whether it is "use-after-free"
> > or "out-of-bound" error instead of "invalid-access" error.This will make
> > it easier for programmers to see the memory corruption problem.
> >
> > Now we extend the quarantine to support both generic and tag-based kasan.
> > For tag-based kasan, the quarantine stores only freed object information
> > to check if an object is freed recently. When tag-based kasan reports an
> > error, we can check if the tagged addr is in the quarantine and make a
> > good guess if the object is more like "use-after-free" or "out-of-bound".
> >
>
>
> We already have all the information and don't need the quarantine to make such guess.
> Basically if shadow of the first byte of object has the same tag as tag in pointer than it's out-of-bounds,
> otherwise it's use-after-free.
>
> In pseudo-code it's something like this:
>
> u8 object_tag = *(u8 *)kasan_mem_to_shadow(nearest_object(cacche, page, access_addr));
>
> if (access_addr_tag == object_tag && object_tag != KASAN_TAG_INVALID)
> // out-of-bounds
> else
> // use-after-free
Thanks your explanation.
I see, we can use it to decide corruption type.
But some use-after-free issues, it may not have accurate free-backtrace.
Unfortunately in that situation, free-backtrace is the most important.
please see below example
In generic KASAN, it gets accurate free-backrace(ptr1).
In tag-based KASAN, it gets wrong free-backtrace(ptr2). It will make
programmer misjudge, so they may not believe tag-based KASAN.
So We provide this patch, we hope tag-based KASAN bug report is the same
accurate with generic KASAN.
---
ptr1 = kmalloc(size, GFP_KERNEL);
ptr1_free(ptr1);
ptr2 = kmalloc(size, GFP_KERNEL);
ptr2_free(ptr2);
ptr1[size] = 'x'; //corruption here
static noinline void ptr1_free(char* ptr)
{
kfree(ptr);
}
static noinline void ptr2_free(char* ptr)
{
kfree(ptr);
}
---
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next prev parent reply other threads:[~2019-06-13 17:47 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 [this message]
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
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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