[PATCH 0/2] drm/panic: Avoid crash from invalid CONFIG_DRM_PANIC_SCREEN values

[PATCH 0/2] drm/panic: Avoid crash from invalid CONFIG_DRM_PANIC_SCREEN values

[Nathan Chancellor]

Hi all,

This series addresses a couple of issues I noticed when accessing
/sys/module/drm/parameters/panic_screen on my Arch Linux machines, which
have "qr_code" as the value of CONFIG_DRM_PANIC_SCREEN. This happened to
be unsupported in my configuration since I was missing some Rust
dependencies in my environment for CONFIG_DRM_PANIC_SCREEN_QR_CODE,
resulting in a kernel crash. Patch one addresses the root cause of the
crash and patch two addresses an inconsistency I noticed between this
new code and the documented value for CONFIG_DRM_PANIC_SCREEN in Kconfig
for qr_code.

If there are any issues, please let me know.

---
Nathan Chancellor (2):
      drm/panic: Ensure drm_panic_type is initialized to a valid value
      drm/panic: Fix expected string for QR_CODE in drm_panic_type_map

 drivers/gpu/drm/drm_panic.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)
---
base-commit: 349d4efadc1f831ebc0b872ba1e3a2b7dd58b72b
change-id: 20260105-drm_panic-handle-invalid-drm_panic_screen-097e49e21c49

Best regards,
--  
Nathan Chancellor <nathan@kernel.org>

[PATCH 1/2] drm/panic: Ensure drm_panic_type is initialized to a valid value

[Nathan Chancellor]

If a user has set an invalid CONFIG_DRM_PANIC_SCREEN value (such as
"qr_code" without CONFIG_DRM_PANIC_SCREEN_QR_CODE=y due to missing or
incorrect Rust dependencies), there is a panic when accessing
/sys/module/drm/parameters/panic_screen:

  [   12.218375] BUG: unable to handle page fault for address: 0000000796dd8818
  [   12.219737] #PF: supervisor read access in kernel mode
  ...
  [   12.227167] RIP: 0010:drm_panic_type_get+0x1b/0x30

If drm_panic_type_set() does not find a valid drm_panic_type enumeration
in drm_panic_type_map based on the provided value, it does not change
drm_panic_type from the default -1 value, which is not a valid index for
accessing drm_panic_type_map in drm_panic_type_get(), resulting in the
crash.

Validate the value of CONFIG_DRM_PANIC_SCREEN at boot time via the
return value of drm_panic_type_set() in drm_panic_init() and explicitly
fall back to the default of "user" with a message to the user so that
they can adjust their configuration or fix missing dependencies.

  [    0.800697] Unsupported value for CONFIG_DRM_PANIC_SCREEN ('qr_code'), falling back to 'user'...

Fixes: e85e9ccf3f84 ("drm/panic: Report invalid or unsupported panic modes")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 drivers/gpu/drm/drm_panic.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
index eb7ef17b9c71..0cd574dd9d88 100644
--- a/drivers/gpu/drm/drm_panic.c
+++ b/drivers/gpu/drm/drm_panic.c
@@ -1072,8 +1072,11 @@ void drm_panic_unregister(struct drm_device *dev)
  */
 void __init drm_panic_init(void)
 {
-	if (drm_panic_type == -1)
-		drm_panic_type_set(CONFIG_DRM_PANIC_SCREEN, NULL);
+	if (drm_panic_type == -1 && drm_panic_type_set(CONFIG_DRM_PANIC_SCREEN, NULL)) {
+		pr_warn("Unsupported value for CONFIG_DRM_PANIC_SCREEN ('%s'), falling back to 'user'...\n",
+			CONFIG_DRM_PANIC_SCREEN);
+		drm_panic_type = DRM_PANIC_TYPE_USER;
+	}
 	drm_panic_qr_init();
 }
 

-- 
2.52.0

[PATCH 2/2] drm/panic: Fix expected string for QR_CODE in drm_panic_type_map

[Nathan Chancellor]

The help text of CONFIG_DRM_PANIC_SCREEN_QR_CODE documents the expected
value to CONFIG_DRM_PANIC_SCREEN as "qr_code" but drm_panic_type_map
checks for "qr". Adjust drm_panic_type_map and the module description to
match so that existing configurations do not stop working.

Fixes: e85e9ccf3f84 ("drm/panic: Report invalid or unsupported panic modes")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 drivers/gpu/drm/drm_panic.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
index 0cd574dd9d88..d6d3b8d85dea 100644
--- a/drivers/gpu/drm/drm_panic.c
+++ b/drivers/gpu/drm/drm_panic.c
@@ -823,7 +823,7 @@ static const char *drm_panic_type_map[] = {
 	[DRM_PANIC_TYPE_KMSG] = "kmsg",
 	[DRM_PANIC_TYPE_USER] = "user",
 #if IS_ENABLED(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
-	[DRM_PANIC_TYPE_QR] = "qr",
+	[DRM_PANIC_TYPE_QR] = "qr_code",
 #endif
 };
 
@@ -855,7 +855,7 @@ static const struct kernel_param_ops drm_panic_ops = {
 module_param_cb(panic_screen, &drm_panic_ops, NULL, 0644);
 MODULE_PARM_DESC(panic_screen,
 #if IS_ENABLED(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
-		 "Choose what will be displayed by drm_panic, 'user', 'kmsg' or 'qr' [default="
+		 "Choose what will be displayed by drm_panic, 'user', 'kmsg' or 'qr_code' [default="
 #else
 		 "Choose what will be displayed by drm_panic, 'user' or 'kmsg' [default="
 #endif

-- 
2.52.0

Re: [PATCH 2/2] drm/panic: Fix expected string for QR_CODE in drm_panic_type_map

[Tvrtko Ursulin]

On 06/01/2026 06:19, Nathan Chancellor wrote:
> The help text of CONFIG_DRM_PANIC_SCREEN_QR_CODE documents the expected
> value to CONFIG_DRM_PANIC_SCREEN as "qr_code" but drm_panic_type_map
> checks for "qr". Adjust drm_panic_type_map and the module description to
> match so that existing configurations do not stop working.
> 
> Fixes: e85e9ccf3f84 ("drm/panic: Report invalid or unsupported panic modes")
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>   drivers/gpu/drm/drm_panic.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
> index 0cd574dd9d88..d6d3b8d85dea 100644
> --- a/drivers/gpu/drm/drm_panic.c
> +++ b/drivers/gpu/drm/drm_panic.c
> @@ -823,7 +823,7 @@ static const char *drm_panic_type_map[] = {
>   	[DRM_PANIC_TYPE_KMSG] = "kmsg",
>   	[DRM_PANIC_TYPE_USER] = "user",
>   #if IS_ENABLED(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
> -	[DRM_PANIC_TYPE_QR] = "qr",
> +	[DRM_PANIC_TYPE_QR] = "qr_code",
>   #endif
>   };
>   
> @@ -855,7 +855,7 @@ static const struct kernel_param_ops drm_panic_ops = {
>   module_param_cb(panic_screen, &drm_panic_ops, NULL, 0644);
>   MODULE_PARM_DESC(panic_screen,
>   #if IS_ENABLED(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
> -		 "Choose what will be displayed by drm_panic, 'user', 'kmsg' or 'qr' [default="
> +		 "Choose what will be displayed by drm_panic, 'user', 'kmsg' or 'qr_code' [default="
>   #else
>   		 "Choose what will be displayed by drm_panic, 'user' or 'kmsg' [default="
>   #endif
> 

Looks like I mistyped when refactoring. Should have used copy and paste, 
sorry about that.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>

Regards,

Tvrtko

Re: [PATCH 1/2] drm/panic: Ensure drm_panic_type is initialized to a valid value

[Tvrtko Ursulin]

On 06/01/2026 06:19, Nathan Chancellor wrote:
> If a user has set an invalid CONFIG_DRM_PANIC_SCREEN value (such as
> "qr_code" without CONFIG_DRM_PANIC_SCREEN_QR_CODE=y due to missing or
> incorrect Rust dependencies), there is a panic when accessing
> /sys/module/drm/parameters/panic_screen:
> 
>    [   12.218375] BUG: unable to handle page fault for address: 0000000796dd8818
>    [   12.219737] #PF: supervisor read access in kernel mode
>    ...
>    [   12.227167] RIP: 0010:drm_panic_type_get+0x1b/0x30
> 
> If drm_panic_type_set() does not find a valid drm_panic_type enumeration
> in drm_panic_type_map based on the provided value, it does not change
> drm_panic_type from the default -1 value, which is not a valid index for
> accessing drm_panic_type_map in drm_panic_type_get(), resulting in the
> crash.
> 
> Validate the value of CONFIG_DRM_PANIC_SCREEN at boot time via the
> return value of drm_panic_type_set() in drm_panic_init() and explicitly
> fall back to the default of "user" with a message to the user so that
> they can adjust their configuration or fix missing dependencies.
> 
>    [    0.800697] Unsupported value for CONFIG_DRM_PANIC_SCREEN ('qr_code'), falling back to 'user'...
> 
> Fixes: e85e9ccf3f84 ("drm/panic: Report invalid or unsupported panic modes")
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>   drivers/gpu/drm/drm_panic.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
> index eb7ef17b9c71..0cd574dd9d88 100644
> --- a/drivers/gpu/drm/drm_panic.c
> +++ b/drivers/gpu/drm/drm_panic.c
> @@ -1072,8 +1072,11 @@ void drm_panic_unregister(struct drm_device *dev)
>    */
>   void __init drm_panic_init(void)
>   {
> -	if (drm_panic_type == -1)
> -		drm_panic_type_set(CONFIG_DRM_PANIC_SCREEN, NULL);
> +	if (drm_panic_type == -1 && drm_panic_type_set(CONFIG_DRM_PANIC_SCREEN, NULL)) {
> +		pr_warn("Unsupported value for CONFIG_DRM_PANIC_SCREEN ('%s'), falling back to 'user'...\n",
> +			CONFIG_DRM_PANIC_SCREEN);
> +		drm_panic_type = DRM_PANIC_TYPE_USER;
> +	}
>   	drm_panic_qr_init();
>   }

I actually tested bad string on the kernel command line but did not 
think to test a bad string in CONFIG_DRM_PANIC_SCREEN. :( And that is 
despite the fact I saw that the kconfig is a free-form input so again my 
bad. Even worse is, I briefly considered converting kconfig to a 
mutually exclusive fixed list but then gave up not wanting to think 
about kconfig backward compatibility issues. We should probably tackle 
that problem since free form inputs are bad. We have another one in DRM 
as well for the fbdev client IIRC.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>

Regards,

Tvrtko

Re: [PATCH 1/2] drm/panic: Ensure drm_panic_type is initialized to a valid value

[Jocelyn Falempe]

On 06/01/2026 07:19, Nathan Chancellor wrote:
> If a user has set an invalid CONFIG_DRM_PANIC_SCREEN value (such as
> "qr_code" without CONFIG_DRM_PANIC_SCREEN_QR_CODE=y due to missing or
> incorrect Rust dependencies), there is a panic when accessing
> /sys/module/drm/parameters/panic_screen:
> 
>    [   12.218375] BUG: unable to handle page fault for address: 0000000796dd8818
>    [   12.219737] #PF: supervisor read access in kernel mode
>    ...
>    [   12.227167] RIP: 0010:drm_panic_type_get+0x1b/0x30
> 
> If drm_panic_type_set() does not find a valid drm_panic_type enumeration
> in drm_panic_type_map based on the provided value, it does not change
> drm_panic_type from the default -1 value, which is not a valid index for
> accessing drm_panic_type_map in drm_panic_type_get(), resulting in the
> crash.
> 
> Validate the value of CONFIG_DRM_PANIC_SCREEN at boot time via the
> return value of drm_panic_type_set() in drm_panic_init() and explicitly
> fall back to the default of "user" with a message to the user so that
> they can adjust their configuration or fix missing dependencies.
> 
>    [    0.800697] Unsupported value for CONFIG_DRM_PANIC_SCREEN ('qr_code'), falling back to 'user'...
> 

Good catch, thanks for the fix.

Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>

> Fixes: e85e9ccf3f84 ("drm/panic: Report invalid or unsupported panic modes")
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>   drivers/gpu/drm/drm_panic.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
> index eb7ef17b9c71..0cd574dd9d88 100644
> --- a/drivers/gpu/drm/drm_panic.c
> +++ b/drivers/gpu/drm/drm_panic.c
> @@ -1072,8 +1072,11 @@ void drm_panic_unregister(struct drm_device *dev)
>    */
>   void __init drm_panic_init(void)
>   {
> -	if (drm_panic_type == -1)
> -		drm_panic_type_set(CONFIG_DRM_PANIC_SCREEN, NULL);
> +	if (drm_panic_type == -1 && drm_panic_type_set(CONFIG_DRM_PANIC_SCREEN, NULL)) {
> +		pr_warn("Unsupported value for CONFIG_DRM_PANIC_SCREEN ('%s'), falling back to 'user'...\n",
> +			CONFIG_DRM_PANIC_SCREEN);
> +		drm_panic_type = DRM_PANIC_TYPE_USER;
> +	}
>   	drm_panic_qr_init();
>   }
>   
> 

Re: [PATCH 2/2] drm/panic: Fix expected string for QR_CODE in drm_panic_type_map

[Jocelyn Falempe]

On 06/01/2026 07:19, Nathan Chancellor wrote:
> The help text of CONFIG_DRM_PANIC_SCREEN_QR_CODE documents the expected
> value to CONFIG_DRM_PANIC_SCREEN as "qr_code" but drm_panic_type_map
> checks for "qr". Adjust drm_panic_type_map and the module description to
> match so that existing configurations do not stop working.

Good catch, thanks for the fix.

Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
> 
> Fixes: e85e9ccf3f84 ("drm/panic: Report invalid or unsupported panic modes")
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>   drivers/gpu/drm/drm_panic.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c
> index 0cd574dd9d88..d6d3b8d85dea 100644
> --- a/drivers/gpu/drm/drm_panic.c
> +++ b/drivers/gpu/drm/drm_panic.c
> @@ -823,7 +823,7 @@ static const char *drm_panic_type_map[] = {
>   	[DRM_PANIC_TYPE_KMSG] = "kmsg",
>   	[DRM_PANIC_TYPE_USER] = "user",
>   #if IS_ENABLED(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
> -	[DRM_PANIC_TYPE_QR] = "qr",
> +	[DRM_PANIC_TYPE_QR] = "qr_code",
>   #endif
>   };
>   
> @@ -855,7 +855,7 @@ static const struct kernel_param_ops drm_panic_ops = {
>   module_param_cb(panic_screen, &drm_panic_ops, NULL, 0644);
>   MODULE_PARM_DESC(panic_screen,
>   #if IS_ENABLED(CONFIG_DRM_PANIC_SCREEN_QR_CODE)
> -		 "Choose what will be displayed by drm_panic, 'user', 'kmsg' or 'qr' [default="
> +		 "Choose what will be displayed by drm_panic, 'user', 'kmsg' or 'qr_code' [default="
>   #else
>   		 "Choose what will be displayed by drm_panic, 'user' or 'kmsg' [default="
>   #endif
> 

Re: [PATCH 0/2] drm/panic: Avoid crash from invalid CONFIG_DRM_PANIC_SCREEN values

[Tvrtko Ursulin]

On 06/01/2026 06:19, Nathan Chancellor wrote:
> Hi all,
> 
> This series addresses a couple of issues I noticed when accessing
> /sys/module/drm/parameters/panic_screen on my Arch Linux machines, which
> have "qr_code" as the value of CONFIG_DRM_PANIC_SCREEN. This happened to
> be unsupported in my configuration since I was missing some Rust
> dependencies in my environment for CONFIG_DRM_PANIC_SCREEN_QR_CODE,
> resulting in a kernel crash. Patch one addresses the root cause of the
> crash and patch two addresses an inconsistency I noticed between this
> new code and the documented value for CONFIG_DRM_PANIC_SCREEN in Kconfig
> for qr_code.
> 
> If there are any issues, please let me know.

I've pushed the series to drm-misc-next, thanks for fixing it up!

Regards,

Tvrtko

> 
> ---
> Nathan Chancellor (2):
>        drm/panic: Ensure drm_panic_type is initialized to a valid value
>        drm/panic: Fix expected string for QR_CODE in drm_panic_type_map
> 
>   drivers/gpu/drm/drm_panic.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> ---
> base-commit: 349d4efadc1f831ebc0b872ba1e3a2b7dd58b72b
> change-id: 20260105-drm_panic-handle-invalid-drm_panic_screen-097e49e21c49
> 
> Best regards,
> --
> Nathan Chancellor <nathan@kernel.org>
>