linux-hardening - Re: [PATCH] s390/vfio-ap: Replace one-element array with flexible array member

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Message-ID: <20250130124647.15115-A-hca@linux.ibm.com>
Date: Thu, 30 Jan 2025 13:46:47 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: Halil Pasic <pasic@...ux.ibm.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Thorsten Blum <thorsten.blum@...ux.dev>,
        Tony Krowiak <akrowiak@...ux.ibm.com>,
        Jason Herne <jjherne@...ux.ibm.com>,
        Harald Freudenberger <freude@...ux.ibm.com>,
        Holger Dengler <dengler@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, linux-hardening@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] s390/vfio-ap: Replace one-element array with flexible
 array member

On Thu, Jan 30, 2025 at 12:37:13PM +0100, Alexander Gordeev wrote:
> On Thu, Jan 30, 2025 at 11:46:15AM +0100, Halil Pasic wrote:
> > > > I'm not sure I understand the value of this. What we have here is not
> > > > a flexible array but a one element array. Something that in the generic
> > > > case could be many but particularly for vfio-ap is always one.  
> > > 
> > > You are correct. Only fake flexible arrays should be transformed into
> > > C99 flex-array members [1].
> > > 
> > > Thanks
> > > -Gustavo
> > > 
> > > [1] https://lwn.net/Articles/908817/
> > > 
> > 
> > Thanks! Alex, what do we do with this then? I think you picked it up
> > yesterday late. And I think, it might make sense to make this look
> > less like a fake flex-array...
> 
> Dropped.
> Thanks for looking into it!

Given that we already have 5dd4241964c8 ("vfio/ccw: replace one-element
array with flexible-array member") applied, we now end up with inconsistent
code. I'd prefer if we address _both_ code locations in a way that the code
looks similar, and people won't send similar patches again and again.

Halil, since you started this discussion, can you address this please?