linux-kernel - Re: [PATCH v2 1/4] drivers: hwspinlock: add generic framework

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Date:	Fri, 26 Nov 2010 12:16:39 +0200
From:	Ohad Ben-Cohen <ohad@...ery.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Olof Johansson <olof@...om.net>,
	Hari Kanigeri <h-kanigeri2@...com>, Suman Anna <s-anna@...com>,
	Benoit Cousson <b-cousson@...com>,
	Arnd Bergmann <arnd@...db.de>,
	Tony Lindgren <tony@...mide.com>, Greg KH <greg@...ah.com>,
	linux-kernel@...r.kernel.org,
	Grant Likely <grant.likely@...retlab.ca>,
	Kevin Hilman <khilman@...prootsystems.com>,
	akpm@...ux-foundation.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/4] drivers: hwspinlock: add generic framework

On Fri, Nov 26, 2010 at 11:18 AM, Russell King - ARM Linux
<linux@....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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