Re: [PATCH] drm/bridge: adv7511: fix crash on irq during probe

[Alvin Šipraga]

Hi Laurent,

Thanks for the quick review!

On Mon, Oct 16, 2023 at 11:14:44AM +0300, Laurent Pinchart wrote:
> Hello Alvin,
> 
> On Sat, Oct 14, 2023 at 08:46:12PM +0200, Alvin Šipraga wrote:
> > From: Mads Bligaard Nielsen <bli@xxxxxxxxxxxxxxx>
> > 
> > Moved IRQ registration down to end of adv7511_probe().
> > 
> > If an IRQ already is pending during adv7511_probe
> > (before adv7511_cec_init) then cec_received_msg_ts
> > could crash using uninitialized data:
> > 
> >     Unable to handle kernel read from unreadable memory at virtual address 00000000000003d5
> >     Internal error: Oops: 96000004 [#1] PREEMPT_RT SMP
> >     Call trace:
> >      cec_received_msg_ts+0x48/0x990 [cec]
> >      adv7511_cec_irq_process+0x1cc/0x308 [adv7511]
> >      adv7511_irq_process+0xd8/0x120 [adv7511]
> >      adv7511_irq_handler+0x1c/0x30 [adv7511]
> >      irq_thread_fn+0x30/0xa0
> >      irq_thread+0x14c/0x238
> >      kthread+0x190/0x1a8
> > 
> > Fixes: 3b1b975003e4 ("drm: adv7511/33: add HDMI CEC support")
> 
> Isn't the issue older than that ?

I don't think so. The stacktrace shows the crash is in CEC handling code, which
was added in the blamed commit. A static analysis of adv7511_irq_process()
suggests that the only other place where data could be uninitialized is if the
hpd_work is scheduled:

	if (process_hpd && irq0 & ADV7511_INT0_HPD && adv7511->bridge.encoder)
		schedule_work(&adv7511->hpd_work);

... but this has a check on bridge.encoder, which seems to have been introduced
in a similar fix here:

| commit a1d0503d26ea2ef04f3f013d379e8f4d29c27127
| Author: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>
| Date:   Thu May 14 00:31:07 2015 +0300
| 
|     drm: adv7511: Fix crash in IRQ handler when no encoder is associated
|     
|     The ADV7511 is probed before its slave encoder init function associates
|     it with an encoder. This creates a time window during which hot plug
|     detection interrupts can occur with an encoder, resulting in a crash in
|     the IRQ handler.
|     
|     Fix this by ignoring hot plug detection IRQs when no encoder is
|     associated yet.
|     
|     Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>
|     Acked-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
| 
| diff --git a/drivers/gpu/drm/i2c/adv7511.c b/drivers/gpu/drm/i2c/adv7511.c
| index b728523e194f..2aaa3c88999e 100644
| --- a/drivers/gpu/drm/i2c/adv7511.c
| +++ b/drivers/gpu/drm/i2c/adv7511.c
| @@ -438,7 +438,7 @@ static int adv7511_irq_process(struct adv7511 *adv7511)
|         regmap_write(adv7511->regmap, ADV7511_REG_INT(0), irq0);
|         regmap_write(adv7511->regmap, ADV7511_REG_INT(1), irq1);
|  
| -       if (irq0 & ADV7511_INT0_HDP)
| +       if (irq0 & ADV7511_INT0_HDP && adv7511->encoder)
|                 drm_helper_hpd_irq_event(adv7511->encoder->dev);
|  
|         if (irq0 & ADV7511_INT0_EDID_READY || irq1 & ADV7511_INT1_DDC_ERROR) {

So assuming that is the case, I am not sure which Fixes: tag I ought to
otherwise use. What do you think?

> 
> > Signed-off-by: Mads Bligaard Nielsen <bli@xxxxxxxxxxxxxxx>
> > Signed-off-by: Alvin Šipraga <alsi@xxxxxxxxxxxxxxx>
> 
> With the Fixes: tag updated,
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>

Kind regards,
Alvin