linux-hardening - Re: [PATCH] [next] drm/amdgpu: Replace one-element array with flexible-array member

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Message-ID: <Y1x3MtRJ8ckXxlJn@mail.google.com>
Date:   Sat, 29 Oct 2022 13:43:30 +1300
From:   Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@...il.com>
To:     Christian König <christian.koenig@....com>
Cc:     Kees Cook <keescook@...omium.org>,
        Alex Deucher <alexander.deucher@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Hans de Goede <hdegoede@...hat.com>,
        Grigory Vasilyev <h0tc0d3@...il.com>,
        Claudio Suarez <cssk@...-c.es>,
        Slark Xiao <slark_xiao@....com>,
        Rongguang Wei <weirongguang@...inos.cn>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] [next] drm/amdgpu: Replace one-element array with
 flexible-array member

On Fri, Oct 28, 2022 at 07:33:17PM +0200, Christian König wrote:
> Am 28.10.22 um 18:36 schrieb Kees Cook:
> 
> > All that said, converting away from them can be tricky, and I think such
> > conversions need to explicitly show how they were checked for binary
> > differences[2].
> 
> Oh, that's a great idea! Yes, if this can be guaranteed then the change is
> obviously perfectly ok.
> 
> > 
> > Paulo, can you please check for deltas and report your findings in the
> > commit log? Note that add struct_size() use in the same patch may result
> > in binary differences, so for more complex cases, you may want to split
> > the 1-element conversion from the struct_size() conversions.
> > 
> > -Kees

Noted. I will reporting my findings on commit logs from now onwards. 

Given that I split the if-ternary to avoid checking "fake_edid_record->ucFakeEDIDLength"
twice then (for the current patch), yes, there will be changes to *.o|ko files.

Knowing that Christian would feel more confident with no binary changes
at this point, I will send a different patch aiming solely on the
replacement of 1-elem array without incurring binary changes.

--
Paulo A.