linux-kernel - Re: [PATCH v5 02/15] drm/edid: Break out reading block 0 of the EDID

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Date:   Mon, 4 Oct 2021 19:13:47 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Steev Klimaszewski <steev@...i.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Linus W <linus.walleij@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Maxime Ripard <mripard@...nel.org>,
        Jani Nikula <jani.nikula@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v5 02/15] drm/edid: Break out reading block 0 of the EDID

Hi Doug,

On Mon, Oct 4, 2021 at 6:26 PM Doug Anderson <dianders@...omium.org> wrote:
> On Mon, Oct 4, 2021 at 8:42 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > -       if ((edid = kmalloc(EDID_LENGTH, GFP_KERNEL)) == NULL)
> > > +       edid = (u8 *)drm_do_get_edid_base_block(get_edid_block, data,
> > > +                                               &connector->edid_corrupt,
> > > +                                               &connector->null_edid_counter);
> > > +       if (IS_ERR_OR_NULL(edid)) {
> > > +               if (IS_ERR(edid))
> >
> > So edid is an error code, not a valid pointer...
> >
> > > +                       connector_bad_edid(connector, edid, 1);
> >
> > ... while connector_bad_edid() expects edid to be a valid pointer,
> > causing a crash:
> >
> > Unable to handle kernel NULL pointer dereference at virtual address
>
> Sigh. Thanks for the report and analysis. I guess I don't have any
> displays reporting invalid EDIDs to test with. Hopefully this will
> help:

It doesn't happen all the time.  Looks like my EDID is only invalid after
a reset needed to resolve an s2ram crash in the adv7511 driver...

> https://lore.kernel.org/r/20211004092100.1.Ic90a5ebd44c75db963112be167a03cc96f9fb249@changeid/

Thanks for the quick fix!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds