linux-kernel - Re: [PATCH 0/2] irqchip/mmp: A pair of robustness fixed

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Date:   Mon, 9 Mar 2020 11:10:20 +0100
From:   Lubomir Rintel <lkundrak@...sk>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        linux-kernel@...r.kernel.org, Rob Herring <robh@...nel.org>
Subject: Re: [PATCH 0/2] irqchip/mmp: A pair of robustness fixed

On Sun, Mar 08, 2020 at 05:26:35PM +0000, Marc Zyngier wrote:
> On Sun, 08 Mar 2020 14:46:04 +0000,
> Lubomir Rintel <lkundrak@...sk> wrote:
> > 
> > On Sun, Mar 08, 2020 at 02:04:34PM +0000, Marc Zyngier wrote:
> > > On Wed, 19 Feb 2020 09:00:22 +0100
> > > Lubomir Rintel <lkundrak@...sk> wrote:
> > > 
> > > [+RobH]
> > > 
> > > Lubomir,
> > > 
> > > > Hi,
> > > > 
> > > > please consider applying these two patches. Thery are not strictly
> > > > necessary, but improve diagnostics in case the DT is faulty.
> > > 
> > > Can't we instead make sure our DT infrastructure checks for these? I'm
> > > very reluctant to add more "DT validation" to the kernel, as it feels
> > > like the wrong place to do this.
> > 
> > These are not really problems of the DT infrastructure.
> 
> They are. The DT bindings describes the constraints (or at least
> should), and the DT infrastructure could, at least in theory, check
> them at compile time. Adding the checks to the kernel defeats the
> single benefit of DT, which is independence from the kernel.
> 
> > It's that the driver has some constrains resulting from use of
> > global data ([PATCH 1]) and statically sized arrays ([PATCH 2])
> > without enforcing them.
> > 
> > It's probably easier to mess up DT than to mess up board files,
> 
> No, both models can be just as easily broken if people write them
> without thinking twice.
> 
> > but regardless of that, being a little defensive and checking the
> > bounds of arrays is probably a good programming practice anyways.
> 
> Is there even any example of such broken DT in the tree?

No, this didn't occur with a FDT build from the kernel tree.

The device tree from Open Firmware that is used on the OLPC XO-4
machine is broken in this way (but it also needs many more fixes in
order to be able to run mainline kernels).

Lubo

> 
> 	M.
> 
> -- 
> Jazz is not dead, it just smells funny.