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From: Ohad Ben-Cohen <ohad@wizery.com>
Date: Fri, 26 Nov 2010 12:16:39 +0200
Message-ID: <AANLkTimS-cSi1B5LdtwhJWhKDuFKOYG1j_p-iQiH=zRe@mail.gmail.com>
Subject: Re: [PATCH v2 1/4] drivers: hwspinlock: add generic framework
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Olof Johansson <olof@lixom.net>, Hari Kanigeri <h-kanigeri2@ti.com>,
        Suman Anna <s-anna@ti.com>, Benoit Cousson <b-cousson@ti.com>,
        Arnd Bergmann <arnd@arndb.de>, Tony Lindgren <tony@atomide.com>,
        Greg KH <greg@kroah.com>, linux-kernel@vger.kernel.org,
        Grant Likely <grant.likely@secretlab.ca>,
        Kevin Hilman <khilman@deeprootsystems.com>, akpm@linux-foundation.org,
        linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org
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On Fri, Nov 26, 2010 at 11:18 AM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Fri, Nov 26, 2010 at 10:53:10AM +0200, Ohad Ben-Cohen wrote:
>> >> +int __hwspin_trylock(struct hwspinlock *hwlock, int mode, unsigned long *flags)
>> >> +{
>> >> + ? ? int ret;
>> >> +
>> >> + ? ? if (unlikely(!hwlock)) {
>> >> + ? ? ? ? ? ? pr_err("invalid hwlock\n");
>> >
>> > These kind of errors can get very spammy for buggy drivers.
>>
>> Yeah, but that's the purpose - I want to catch such egregious drivers
>> who try to crash the kernel.
>
> That can be better - because you get a backtrace, and it causes people
> to report the problem rather than just ignore it. ?It may also prevent
> the driver author releasing his code (as it won't work on their
> initial testing.)
>
...
>
> If it's "extremely buggy behaviour" then the drivers deserve to crash.
> Such stuff should cause them not to get out the door. ?A simple printk
> with an error return can just be ignored.

I like this approach too, but recently we had a few privilege
escalation exploits which involved NULL dereference kernel bugs
(process context mapped address 0 despite a positive mmap_min_addr).

Since we can't rely on the oops to always happen, I decided not to
omit the NULL checks.

>
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