linux-kernel - Re: [PATCH] ARM: EXYNOS: use BUG

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <50A11B3B.1080600@oracle.com>
Date:	Mon, 12 Nov 2012 10:52:27 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Maarten Lankhorst <m.b.lankhorst@...il.com>,
	linux-kernel@...r.kernel.org, Kukjin Kim <kgene.kim@...sung.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH] ARM: EXYNOS: use BUG_ON where possible

On 11/12/2012 10:23 AM, Russell King - ARM Linux wrote:
> On Mon, Nov 12, 2012 at 04:12:29PM +0100, Maarten Lankhorst wrote:
>> Op 08-11-12 21:23, Sasha Levin schreef:
>>> @@ -465,10 +465,8 @@ static void __init combiner_cascade_irq(unsigned int combiner_nr, unsigned int i
>>>  	else
>>>  		max_nr = EXYNOS4_MAX_COMBINER_NR;
>>>  
>>> -	if (combiner_nr >= max_nr)
>>> -		BUG();
>>> -	if (irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0)
>>> -		BUG();
>>> +	BUG_ON(combiner_nr >= max_nr);
>>> +	BUG_ON(irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0);
>>
>> Is it really a good idea to put functions that perform work in a BUG_ON?
>> I don't know, but for some reason it just feels wrong. I'd expect code to
>> compile fine if BUG_ON was a noop, so doing verification calls only, not
>> actual work..
> 
> Well, it is currently defined as:
> 
> include/asm-generic/bug.h:#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while(0)
> include/asm-generic/bug.h:#define BUG_ON(condition) do { if (condition) ; } while(0)
> 
> but as these can be overridden, I don't think relying on those
> implementations is a good idea; to do so would be fragile.  Eg, what if
> the BUG_ON() implementation becomes just:
> 
> #define BUG_ON(x)
> 
> then the function call itself vanishes.  So, only put the actual bug test
> inside a BUG_ON(), not the functional part which must always be executed.

Even if we ignore that modifying the side-effects is wrong, there's already
more than enough code in the kernel (both in kernel/ / mm/, and in arch/) to
cause breakage if for some reason the expression is not evaluated.

If some arch decides to not evaluate the expression there it's going to be
inherently broken.


Thanks,
Sasha


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/