[PATCH v2] drm/omap: dsi: do not copy isr table

[PATCH v2] drm/omap: dsi: do not copy isr table

[Andreas Kemnade]

To te able to unregister stuff from isrs, the corresponding table was
copied.  Nobody seems to unregister stuff that way, so it does not help.
But there are stack-allocated objects passed to these isrs giving chances
of UAF of these objects if irqs are unregistered while they are handled,
so better do not copy that table.

Fixes: 4ae2ddddf44cd ("OMAP: DSS2: DSI: Add ISR support")
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
---
If this gets backported, it should be re-checked that
no isr unregisters itself in older kernel versions`.
---
Changes in v2:
- remove variable definition (Sashiko)
- Link to v1: https://patch.msgid.link/20260629-dsi-uaf-v1-1-a5e894f4e4d1@kemnade.info

To: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
To: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
To: Maxime Ripard <mripard@kernel.org>
To: Thomas Zimmermann <tzimmermann@suse.de>
To: David Airlie <airlied@gmail.com>
To: Simona Vetter <simona@ffwll.ch>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
---
 drivers/gpu/drm/omapdrm/dss/dsi.c | 7 +------
 drivers/gpu/drm/omapdrm/dss/dsi.h | 2 --
 2 files changed, 1 insertion(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/omapdrm/dss/dsi.c b/drivers/gpu/drm/omapdrm/dss/dsi.c
index 27fe7bca9e2c..70cfb779d6ae 100644
--- a/drivers/gpu/drm/omapdrm/dss/dsi.c
+++ b/drivers/gpu/drm/omapdrm/dss/dsi.c
@@ -455,15 +455,10 @@ static irqreturn_t omap_dsi_irq_handler(int irq, void *arg)
 		timer_delete(&dsi->te_timer);
 #endif
 
-	/* make a copy and unlock, so that isrs can unregister
-	 * themselves */
-	memcpy(&dsi->isr_tables_copy, &dsi->isr_tables,
-		sizeof(dsi->isr_tables));
+	dsi_handle_isrs(&dsi->isr_tables, irqstatus, vcstatus, ciostatus);
 
 	spin_unlock(&dsi->irq_lock);
 
-	dsi_handle_isrs(&dsi->isr_tables_copy, irqstatus, vcstatus, ciostatus);
-
 	dsi_handle_irq_errors(dsi, irqstatus, vcstatus, ciostatus);
 
 	dsi_collect_irq_stats(dsi, irqstatus, vcstatus, ciostatus);
diff --git a/drivers/gpu/drm/omapdrm/dss/dsi.h b/drivers/gpu/drm/omapdrm/dss/dsi.h
index 601707c0ecc4..2b25247ea893 100644
--- a/drivers/gpu/drm/omapdrm/dss/dsi.h
+++ b/drivers/gpu/drm/omapdrm/dss/dsi.h
@@ -379,8 +379,6 @@ struct dsi_data {
 
 	spinlock_t irq_lock;
 	struct dsi_isr_tables isr_tables;
-	/* space for a copy used by the interrupt handler */
-	struct dsi_isr_tables isr_tables_copy;
 
 	int update_vc;
 #ifdef DSI_PERF_MEASURE

---
base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
change-id: 20260629-dsi-uaf-71bfbf3553bf

Best regards,
--  
Andreas Kemnade <andreas@kemnade.info>

Re: [PATCH v2] drm/omap: dsi: do not copy isr table

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Missed fix / Use-After-Free in fbdev omapfb driver
--

commit 84bfbe9de64eb5f62f575283f7f6c859c07c8287
Author: Andreas Kemnade <andreas@kemnade.info>

drm/omap: dsi: do not copy isr table

This commit stops copying the ISR table in the OMAP DSI interrupt handler
to prevent potential use-after-free vulnerabilities. By directly handling
ISRs with the original table, it avoids accessing stack-allocated objects
that might have been unregistered and destroyed.

> diff --git a/drivers/gpu/drm/omapdrm/dss/dsi.c b/drivers/gpu/drm/omapdrm/dss/dsi.c
> index 27fe7bca9e2cf..70cfb779d6ae5 100644
> --- a/drivers/gpu/drm/omapdrm/dss/dsi.c
> +++ b/drivers/gpu/drm/omapdrm/dss/dsi.c
> @@ -455,15 +455,10 @@ static irqreturn_t omap_dsi_irq_handler(int irq, void *arg)
>  		timer_delete(&dsi->te_timer);
>  #endif
>  
> -	/* make a copy and unlock, so that isrs can unregister
> -	 * themselves */
> -	memcpy(&dsi->isr_tables_copy, &dsi->isr_tables,
> -		sizeof(dsi->isr_tables));
> +	dsi_handle_isrs(&dsi->isr_tables, irqstatus, vcstatus, ciostatus);

[Severity: High]
This is a pre-existing issue, but does the same vulnerability still exist
in the fbdev omapfb driver?

Looking at drivers/video/fbdev/omap2/omapfb/dss/dsi.c in omap_dsi_irq_handler(),
it still contains the copied table pattern:

	/* make a copy and unlock, so that isrs can unregister
	 * themselves */
	memcpy(&dsi->isr_tables_copy, &dsi->isr_tables,
		sizeof(dsi->isr_tables));

	spin_unlock(&dsi->irq_lock);

	dsi_handle_isrs(&dsi->isr_tables_copy, irqstatus, vcstatus, ciostatus);

If a timed-out waiter unregisters its ISR and its on-stack completion object
is destroyed, could the interrupt handler still access it via the copied
isr_tables_copy table?

Should this fix be applied to the fbdev driver as well?

>  
>  	spin_unlock(&dsi->irq_lock);
>  
> -	dsi_handle_isrs(&dsi->isr_tables_copy, irqstatus, vcstatus, ciostatus);
> -
>  	dsi_handle_irq_errors(dsi, irqstatus, vcstatus, ciostatus);
>  
>  	dsi_collect_irq_stats(dsi, irqstatus, vcstatus, ciostatus);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260702-dsi-uaf-v2-1-dbb4aa0f0b8e@kemnade.info?part=1