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From:   Jann Horn <jannh@google.com>
Date:   Mon, 7 Nov 2022 22:48:20 +0100
Message-ID: <CAG48ez2-xUawSs4ji_+0Bnyn_QTiS930UiOypXreU_RhwhVo_w@mail.gmail.com>
Subject: Re: [PATCH] exit: Put an upper limit on how often we can oops
To:     Solar Designer <solar@openwall.com>
Cc:     Kees Cook <keescook@chromium.org>, linux-hardening@vger.kernel.org,
        kernel-hardening@lists.openwall.com,
        Greg KH <gregkh@linuxfoundation.org>,
        Linus Torvalds <torvalds@linuxfoundation.org>,
        Seth Jenkins <sethjenkins@google.com>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Andy Lutomirski <luto@kernel.org>, linux-kernel@vger.kernel.org
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On Mon, Nov 7, 2022 at 10:15 PM Solar Designer <solar@openwall.com> wrote:
> On Mon, Nov 07, 2022 at 09:13:17PM +0100, Jann Horn wrote:
> > +oops_limit
> > +==========
> > +
> > +Number of kernel oopses after which the kernel should panic when
> > +``panic_on_oops`` is not set.
>
> Rather than introduce this separate oops_limit, how about making
> panic_on_oops (and maybe all panic_on_*) take the limit value(s) instead
> of being Boolean?  I think this would preserve the current behavior at
> panic_on_oops = 0 and panic_on_oops = 1, but would introduce your
> desired behavior at panic_on_oops = 10000.  We can make 10000 the new
> default.  If a distro overrides panic_on_oops, it probably sets it to 1
> like RHEL does.
>
> Are there distros explicitly setting panic_on_oops to 0?  If so, that
> could be a reason to introduce the separate oops_limit.
>
> I'm not advocating one way or the other - I just felt this should be
> explicitly mentioned and decided on.

I think at least internally in the kernel, it probably works better to
keep those two concepts separate? For example, sparc has a function
die_nmi() that uses panic_on_oops to determine whether the system
should panic when a watchdog detects a lockup.