linux-kernel - Re: [PATCH v4 08/11] mtd: brcmnand: add BCM63138 support

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Date:	Wed, 13 May 2015 22:48:19 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Brian Norris <computersforpeace@...il.com>
Cc:	linux-mtd@...ts.infradead.org, Dmitry Torokhov <dtor@...gle.com>,
	Anatol Pomazao <anatol@...gle.com>,
	Ray Jui <rjui@...adcom.com>,
	Corneliu Doban <cdoban@...adcom.com>,
	Jonathan Richardson <jonathar@...adcom.com>,
	Scott Branden <sbranden@...adcom.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Rafał Miłecki <zajec5@...il.com>,
	bcm-kernel-feedback-list@...adcom.com,
	Dan Ehrenberg <dehrenberg@...omium.org>,
	Gregory Fong <gregory.0xf0@...il.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Kevin Cernekee <cernekee@...il.com>
Subject: Re: [PATCH v4 08/11] mtd: brcmnand: add BCM63138 support

On Wednesday 13 May 2015 13:24:15 Brian Norris wrote:
> > > 
> > > static int bcm63138_nand_probe(...)
> > > {
> > >     struct bcm63138_nand_soc *priv;
> > > 
> > >     priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> > >     ...
> > >     return brcmnand_probe(pdev, &priv->soc);
> > > }
> > 
> > That would make struct brcmnand_soc an empty structure, right?
> 
> No, it still contains the function pointers for our callbacks, which is
> the entire point. I guess it's more of a 'nand_soc_ops' structure than a
> 'nand_soc' pointer now though.
> 

Ah, I see.

This is fine for a small number of function pointers, but if you ever
get a structure like this with a lot of pointers, it's better to
keep them separate, so you can define the structure of function pointers
as 'static const' in the client driver, as we do for a number of
other operations.

The main advantage of that is that you don't have to assign the members
manually at run-time, but also putting them into the read-only segment
makes it harder for an attacker to overwrite a known function pointer
with a pointer to an exploit (assuming they have limited control over
writing to kernel memory).

	Arnd
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