Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v2] Add kernel config option for fuzz testing.
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Andrew Morton <akpm@linux-foundation.org>,
        Matthew Garrett <mjg59@google.com>,
        Andi Kleen <ak@linux.intel.com>,
        "Theodore Y . Ts'o" <tytso@mit.edu>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>
References: <20200307135822.3894-1-penguin-kernel@I-love.SAKURA.ne.jp>
 <6f2e27de-c820-7de3-447d-cd9f7c650add@suse.com>
 <20200308065258.GE3983392@kroah.com>
From:   Jiri Slaby <jslaby@suse.com>
Autocrypt: addr=jslaby@suse.com; prefer-encrypt=mutual; keydata=
 mQINBE6S54YBEACzzjLwDUbU5elY4GTg/NdotjA0jyyJtYI86wdKraekbNE0bC4zV+ryvH4j
 rrcDwGs6tFVrAHvdHeIdI07s1iIx5R/ndcHwt4fvI8CL5PzPmn5J+h0WERR5rFprRh6axhOk
 rSD5CwQl19fm4AJCS6A9GJtOoiLpWn2/IbogPc71jQVrupZYYx51rAaHZ0D2KYK/uhfc6neJ
 i0WqPlbtIlIrpvWxckucNu6ZwXjFY0f3qIRg3Vqh5QxPkojGsq9tXVFVLEkSVz6FoqCHrUTx
 wr+aw6qqQVgvT/McQtsI0S66uIkQjzPUrgAEtWUv76rM4ekqL9stHyvTGw0Fjsualwb0Gwdx
 ReTZzMgheAyoy/umIOKrSEpWouVoBt5FFSZUyjuDdlPPYyPav+hpI6ggmCTld3u2hyiHji2H
 cDpcLM2LMhlHBipu80s9anNeZhCANDhbC5E+NZmuwgzHBcan8WC7xsPXPaiZSIm7TKaVoOcL
 9tE5aN3jQmIlrT7ZUX52Ff/hSdx/JKDP3YMNtt4B0cH6ejIjtqTd+Ge8sSttsnNM0CQUkXps
 w98jwz+Lxw/bKMr3NSnnFpUZaxwji3BC9vYyxKMAwNelBCHEgS/OAa3EJoTfuYOK6wT6nadm
 YqYjwYbZE5V/SwzMbpWu7Jwlvuwyfo5mh7w5iMfnZE+vHFwp/wARAQABtBxKaXJpIFNsYWJ5
 IDxqc2xhYnlAc3VzZS5jb20+iQI4BBMBAgAiBQJOkujrAhsDBgsJCAcDAgYVCAIJCgsEFgID
 AQIeAQIXgAAKCRC9JbEEBrRwSc1VD/9CxnyCYkBrzTfbi/F3/tTstr3cYOuQlpmufoEjCIXx
 PNnBVzP7XWPaHIUpp5tcweG6HNmHgnaJScMHHyG83nNAoCEPihyZC2ANQjgyOcnzDOnW2Gzf
 8v34FDQqj8CgHulD5noYBrzYRAss6K42yUxUGHOFI1Ky1602OCBRtyJrMihio0gNuC1lE4YZ
 juGZEU6MYO1jKn8QwGNpNKz/oBs7YboU7bxNTgKrxX61cSJuknhB+7rHOQJSXdY02Tt31R8G
 diot+1lO/SoB47Y0Bex7WGTXe13gZvSyJkhZa5llWI/2d/s1aq5pgrpMDpTisIpmxFx2OEkb
 jM95kLOs/J8bzostEoEJGDL4u8XxoLnOEjWyT82eKkAe4j7IGQlA9QQR2hCMsBdvZ/EoqTcd
 SqZSOto9eLQkjZLz0BmeYIL8SPkgnVAJ/FEK44NrHUGzjzdkE7a0jNvHt8ztw6S+gACVpysi
 QYo2OH8hZGaajtJ8mrgN2Lxg7CpQ0F6t/N1aa/+A2FwdRw5sHBqA4PH8s0Apqu66Q94YFzzu
 8OWkSPLgTjtyZcez79EQt02u8xH8dikk7API/PYOY+462qqbahpRGaYdvloaw7tOQJ224pWJ
 4xePwtGyj4raAeczOcBQbKKW6hSH9iz7E5XUdpJqO3iZ9psILk5XoyO53wwhsLgGcrkCDQRO
 kueGARAAz5wNYsv5a9z1wuEDY5dn+Aya7s1tgqN+2HVTI64F3l6Yg753hF8UzTZcVMi3gzHC
 ECvKGwpBBwDiJA2V2RvJ6+Jis8paMtONFdPlwPaWlbOv4nHuZfsidXkk7PVCr4/6clZggGNQ
 qEjTe7Hz2nnwJiKXbhmnKfYXlxftT6KdjyUkgHAs8Gdz1nQCf8NWdQ4P7TAhxhWdkAoOIhc4
 OQapODd+FnBtuL4oCG0c8UzZ8bDZVNR/rYgfNX54FKdqbM84FzVewlgpGjcUc14u5Lx/jBR7
 ttZv07ro88Ur9GR6o1fpqSQUF/1V+tnWtMQoDIna6p/UQjWiVicQ2Tj7TQgFr4Fq8ZDxRb10
 Zbeds+t+45XlRS9uexJDCPrulJ2sFCqKWvk3/kf3PtUINDR2G4k228NKVN/aJQUGqCTeyaWf
 fU9RiJU+sw/RXiNrSL2q079MHTWtN9PJdNG2rPneo7l0axiKWIk7lpSaHyzBWmi2Arj/nuHf
 Maxpc708aCecB2p4pUhNoVMtjUhKD4+1vgqiWKI6OsEyZBRIlW2RRcysIwJ648MYejvf1dzv
 mVweUa4zfIQH/+G0qPKmtst4t/XLjE/JN54XnOD/TO1Fk0pmJyASbHJQ0EcecEodDHPWP6bM
 fQeNlm1eMa7YosnXwbTurR+nPZk+TYPndbDf1U0j8n0AEQEAAYkCHwQYAQIACQUCTpLnhgIb
 DAAKCRC9JbEEBrRwSTe1EACA74MWlvIhrhGWd+lxbXsB+elmL1VHn7Ovj3qfaMf/WV3BE79L
 5A1IDyp0AGoxv1YjgE1qgA2ByDQBLjb0yrS1ppYqQCOSQYBPuYPVDk+IuvTpj/4rN2v3R5RW
 d6ozZNRBBsr4qHsnCYZWtEY2pCsOT6BE28qcbAU15ORMq0nQ/yNh3s/WBlv0XCP1gvGOGf+x
 UiE2YQEsGgjs8v719sguok8eADBbfmumerh/8RhPKRuTWxrXdNq/pu0n7hA6Btx7NYjBnnD8
 lV8Qlb0lencEUBXNFDmdWussMAlnxjmKhZyb30m1IgjFfG30UloZzUGCyLkr/53JMovAswmC
 IHNtXHwb58Ikn1i2U049aFso+WtDz4BjnYBqCL1Y2F7pd8l2HmDqm2I4gubffSaRHiBbqcSB
 lXIjJOrd6Q66u5+1Yv32qk/nOL542syYtFDH2J5wM2AWvfjZH1tMOVvVMu5Fv7+0n3x/9shY
 ivRypCapDfcWBGGsbX5eaXpRfInaMTGaU7wmWO44Z5diHpmQgTLOrN9/MEtdkK6OVhAMVenI
 w1UnZnA+ZfaZYShi5oFTQk3vAz7/NaA5/bNHCES4PcDZw7Y/GiIh/JQR8H1JKZ99or9LjFeg
 HrC8YQ1nzkeDfsLtYM11oC3peHa5AiXLmCuSC9ammQ3LhkfET6N42xTu2A==
Message-ID: <3e9f47f7-a6c1-7cec-a84f-e621ae5426be@suse.com>
Date:   Mon, 9 Mar 2020 16:39:47 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.5.0
MIME-Version: 1.0
In-Reply-To: <20200308065258.GE3983392@kroah.com>
Content-Type: text/plain; charset=iso-8859-2
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 08. 03. 20, 7:52, Greg Kroah-Hartman wrote:
> On Sat, Mar 07, 2020 at 05:28:22PM +0100, Jiri Slaby wrote:
>> On 07. 03. 20, 14:58, Tetsuo Handa wrote:
>>> While syzkaller is finding many bugs, sometimes syzkaller examines
>>> stupid operations. Currently we prevent syzkaller from examining
>>> stupid operations by blacklisting syscall arguments and/or disabling
>>> whole functionality using existing kernel config options, but it is
>>> a whack-a-mole approach. We need cooperation from kernel side [1].
>>>
>>> This patch introduces a kernel config option which allows disabling
>>> only specific operations. This kernel config option should be enabled
>>> only when building kernels for fuzz testing.
>>>
>>> We discussed possibility of disabling specific operations at run-time
>>> using some lockdown mechanism [2], but conclusion seems that build-time
>>> control (i.e. kernel config option) fits better for this purpose.
>>> Since patches for users of this kernel config option will want a lot of
>>> explanation [3], this patch provides only kernel config option for them.
>>>
>>> [1] https://github.com/google/syzkaller/issues/1622
>>> [2] https://lkml.kernel.org/r/CACdnJutc7OQeoor6WLTh8as10da_CN=crs79v3Fp0mJTaO=+yw@mail.gmail.com
>>> [3] https://lkml.kernel.org/r/20191216163155.GB2258618@kroah.com
>>>
>>> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>>> Cc: Dmitry Vyukov <dvyukov@google.com>
>>> ---
>>>  lib/Kconfig.debug | 10 ++++++++++
>>>  1 file changed, 10 insertions(+)
>>>
>>> Changes since v1:
>>>   Drop users of this kernel config option.
>>>   Update patch description.
>>>
>>> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
>>> index 53e786e0a604..e360090e24c5 100644
>>> --- a/lib/Kconfig.debug
>>> +++ b/lib/Kconfig.debug
>>> @@ -2208,4 +2208,14 @@ config HYPERV_TESTING
>>>  
>>>  endmenu # "Kernel Testing and Coverage"
>>>  
>>> +config KERNEL_BUILT_FOR_FUZZ_TESTING
>>> +       bool "Build kernel for fuzz testing"
>>
>> If we really want to go this way, I wouldn't limit it for fuzz testing
>> only. Static analyzers, symbolic executors, formal verifiers, etc. --
>> all of them should avoid the paths.
> 
> No, anything that just evaluates the code should be fine, we want static
> analyzers to be processing those code paths.  Just not to run them as
> root on a live system.

Even static analyzers generate real-world counter-examples in .c. They
are ran dynamically to check if the issue is real or if it's only a
shortcoming of static analysis. Klee is one of those and I used to run
it on the kernel some time ago. Throwing such generated input results in
the same weird behavior as using fuzzy testing, while it's still not
fuzzy testing, but accurate testing.

thanks,
-- 
js
suse labs