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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 3 Feb 2020 14:08:32 -0000 Received: from b06wcsmtp001.portsmouth.uk.ibm.com (b06wcsmtp001.portsmouth.uk.ibm.com [9.149.105.160]) by b06avi18878370.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 013E8VcA32440800 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 3 Feb 2020 14:08:31 GMT Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 31782A405C; Mon, 3 Feb 2020 14:08:31 +0000 (GMT) Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A6E1BA4062; Mon, 3 Feb 2020 14:08:30 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.152.99.16]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 3 Feb 2020 14:08:30 +0000 (GMT) Subject: Re: [PATCH 1/1] mm: sysctl: add panic_on_inconsistent_mm sysctl To: Qian Cai , Grzegorz Halat Cc: Linux Kernel Mailing List , Linux-MM , linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, ssaner@redhat.com, atomlin@redhat.com, oleksandr@redhat.com, vbendel@redhat.com, kirill@shutemov.name, khlebnikov@yandex-team.ru, Andrew Morton , Iurii Zaikin , Kees Cook , Luis Chamberlain , Jonathan Corbet , Tetsuo Handa References: <20200129180851.551109-1-ghalat@redhat.com> <84C253EB-B348-4B62-B863-F192FBA8C202@lca.pw> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <84C253EB-B348-4B62-B863-F192FBA8C202@lca.pw> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-TM-AS-GCONF: 00 x-cbid: 20020314-0008-0000-0000-0000034F4DD3 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20020314-0009-0000-0000-00004A6FD797 Message-Id: <34467005-1742-47a0-cd2b-05567584b91e@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.572 definitions=2020-02-03_04:2020-02-02,2020-02-03 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 malwarescore=0 suspectscore=27 priorityscore=1501 bulkscore=0 phishscore=0 lowpriorityscore=0 impostorscore=0 mlxlogscore=808 clxscore=1015 mlxscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1911200001 definitions=main-2002030106 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 29.01.20 19:39, Qian Cai wrote: >=20 >=20 >> On Jan 29, 2020, at 1:08 PM, Grzegorz Halat wrote: >> >> Memory management subsystem performs various checks at runtime, >> if an inconsistency is detected then such event is being logged and ke= rnel >> continues to run. While debugging such problems it is helpful to colle= ct >> memory dump as early as possible. Currently, there is no easy way to p= anic >> kernel when such error is detected. >> >> It was proposed[1] to panic the kernel if panic_on_oops is set but thi= s >> approach was not accepted. One of alternative proposals was introducti= on of >> a new sysctl. >> >> Add a new sysctl - panic_on_inconsistent_mm. If the sysctl is set then= the >> kernel will be crashed when an inconsistency is detected by memory >> management. This currently means panic when bad page or bad PTE >> is detected(this may be extended to other places in MM). >> >> Another use case of this sysctl may be in security-wise environments, >> it may be more desired to crash machine than continue to run with >> potentially damaged data structures. >=20 > It is annoying that I have to repeat my feedback, but I don=E2=80=99t k= now why > admins want to enable this by allowing normal users to crash the system= s > more easily through recoverable MM bugs where I am sure we have plenty. > How does that improve the security? There are cases where data corruption is a no-go, while "one node going d= own"=20 is acceptable. And then there is also the case for payed service providers that often ne= ed a dump at the time of the problem to understand rare issues. So I DO see value in such a thing. We should just piggy-back on panic_on_= warn I guess.