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;
Message-ID: <1580742371.7365.1.camel@lca.pw>
Subject: Re: [PATCH 1/1] mm: sysctl: add panic_on_inconsistent_mm sysctl
From:   Qian Cai <cai@lca.pw>
To:     Christian Borntraeger <borntraeger@de.ibm.com>,
        Grzegorz Halat <ghalat@redhat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>, 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 <akpm@linux-foundation.org>,
        Iurii Zaikin <yzaikin@google.com>,
        Kees Cook <keescook@chromium.org>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Date:   Mon, 03 Feb 2020 10:06:11 -0500
In-Reply-To: <34467005-1742-47a0-cd2b-05567584b91e@de.ibm.com>
References: <20200129180851.551109-1-ghalat@redhat.com>
         <84C253EB-B348-4B62-B863-F192FBA8C202@lca.pw>
         <34467005-1742-47a0-cd2b-05567584b91e@de.ibm.com>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, 2020-02-03 at 15:08 +0100, Christian Borntraeger wrote:
> 
> On 29.01.20 19:39, Qian Cai wrote:
> > 
> > 
> > > On Jan 29, 2020, at 1:08 PM, Grzegorz Halat <ghalat@redhat.com> wrote:
> > > 
> > > Memory management subsystem performs various checks at runtime,
> > > if an inconsistency is detected then such event is being logged and kernel
> > > continues to run. While debugging such problems it is helpful to collect
> > > memory dump as early as possible. Currently, there is no easy way to panic
> > > kernel when such error is detected.
> > > 
> > > It was proposed[1] to panic the kernel if panic_on_oops is set but this
> > > approach was not accepted. One of alternative proposals was introduction 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.
> > 
> > It is annoying that I have to repeat my feedback, but I don’t know why
> > admins want to enable this by allowing normal users to crash the systems
> > 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 down" 
> is acceptable.
> And then there is also the case for payed service providers that often need
> 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.
> 

Indeed, so change pr_alert() to pr_warn() there then?