[PATCH] drm/imx: fix out of bounds array access warning

[PATCH] drm/imx: fix out of bounds array access warning

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

When CONFIG_OF is disabled, building with 'make W=1' produces warnings
about out of bounds array access:

drivers/gpu/drm/imx/imx-ldb.c: In function 'imx_ldb_set_clock.constprop':
drivers/gpu/drm/imx/imx-ldb.c:186:8: error: array subscript -22 is below array bounds of 'struct clk *[4]' [-Werror=array-bounds]

Add an error check before the index is used, which helps with the
warning, as well as any possible other error condition that may be
triggered at runtime.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/gpu/drm/imx/imx-ldb.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/imx/imx-ldb.c b/drivers/gpu/drm/imx/imx-ldb.c
index dbfe39e2f7f6..1210360cec8a 100644
--- a/drivers/gpu/drm/imx/imx-ldb.c
+++ b/drivers/gpu/drm/imx/imx-ldb.c
@@ -197,6 +197,12 @@ static void imx_ldb_encoder_enable(struct drm_encoder *encoder)
 	int dual = ldb->ldb_ctrl & LDB_SPLIT_MODE_EN;
 	int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);
 
+	if (mux < 0) {
+		dev_warn(ldb->dev,
+			 "%s: invalid mux\n", __func__);
+		return;
+	}
+
 	drm_panel_prepare(imx_ldb_ch->panel);
 
 	if (dual) {
@@ -255,6 +261,12 @@ imx_ldb_encoder_atomic_mode_set(struct drm_encoder *encoder,
 	int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);
 	u32 bus_format = imx_ldb_ch->bus_format;
 
+	if (mux < 0) {
+		dev_warn(ldb->dev,
+			 "%s: invalid mux\n", __func__);
+		return;
+	}
+
 	if (mode->clock > 170000) {
 		dev_warn(ldb->dev,
 			 "%s: mode exceeds 170 MHz pixel clock\n", __func__);
-- 
2.29.2

Re: [PATCH] drm/imx: fix out of bounds array access warning

[Fabio Estevam]

Hi Arnd,

On Tue, Mar 23, 2021 at 10:05 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> When CONFIG_OF is disabled, building with 'make W=1' produces warnings
> about out of bounds array access:
>
> drivers/gpu/drm/imx/imx-ldb.c: In function 'imx_ldb_set_clock.constprop':
> drivers/gpu/drm/imx/imx-ldb.c:186:8: error: array subscript -22 is below array bounds of 'struct clk *[4]' [-Werror=array-bounds]

What about making the driver depend on OF instead (like it is done in
DRM_IMX_HDMI) ?

--- a/drivers/gpu/drm/imx/Kconfig
+++ b/drivers/gpu/drm/imx/Kconfig
@@ -27,7 +27,7 @@ config DRM_IMX_TVE

 config DRM_IMX_LDB
        tristate "Support for LVDS displays"
-       depends on DRM_IMX && MFD_SYSCON
+       depends on DRM_IMX && MFD_SYSCON && OF
        depends on COMMON_CLK
        select DRM_PANEL
        help

Re: [PATCH] drm/imx: fix out of bounds array access warning

[Liu Ying]

Hi Fabio,

On Tue, 2021-03-23 at 11:02 -0300, Fabio Estevam wrote:
> Hi Arnd,
> 
> On Tue, Mar 23, 2021 at 10:05 AM Arnd Bergmann <arnd@kernel.org> wrote:
> > From: Arnd Bergmann <arnd@arndb.de>
> > 
> > When CONFIG_OF is disabled, building with 'make W=1' produces warnings
> > about out of bounds array access:
> > 
> > drivers/gpu/drm/imx/imx-ldb.c: In function 'imx_ldb_set_clock.constprop':
> > drivers/gpu/drm/imx/imx-ldb.c:186:8: error: array subscript -22 is below array bounds of 'struct clk *[4]' [-Werror=array-bounds]
> 
> What about making the driver depend on OF instead (like it is done in
> DRM_IMX_HDMI) ?

The below patch made DRM_IMX_HDMI depend on OF,
because of_drm_find_bridge() is not defined when OF is disabled.

drm/imx: dw_hdmi-imx: depend on OF to fix randconfig compile tests on
x86_64

It doesn't look like DRM_IMX_LDB is in the same case.


Moreover, even if OF is enabled, drm_of_encoder_active_endpoint() is
likely to return -EINVAL.  So, it looks ok to add an error check.

Regards,
Liu Ying

> 
> --- a/drivers/gpu/drm/imx/Kconfig
> +++ b/drivers/gpu/drm/imx/Kconfig
> @@ -27,7 +27,7 @@ config DRM_IMX_TVE
> 
>  config DRM_IMX_LDB
>         tristate "Support for LVDS displays"
> -       depends on DRM_IMX && MFD_SYSCON
> +       depends on DRM_IMX && MFD_SYSCON && OF
>         depends on COMMON_CLK
>         select DRM_PANEL
>         help

Re: [PATCH] drm/imx: fix out of bounds array access warning

[Joe Perches]

On Tue, 2021-03-23 at 14:05 +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> When CONFIG_OF is disabled, building with 'make W=1' produces warnings
> about out of bounds array access:
> 
> drivers/gpu/drm/imx/imx-ldb.c: In function 'imx_ldb_set_clock.constprop':
> drivers/gpu/drm/imx/imx-ldb.c:186:8: error: array subscript -22 is below array bounds of 'struct clk *[4]' [-Werror=array-bounds]
> 
> Add an error check before the index is used, which helps with the
> warning, as well as any possible other error condition that may be
> triggered at runtime.
[]
> diff --git a/drivers/gpu/drm/imx/imx-ldb.c b/drivers/gpu/drm/imx/imx-ldb.c
[]
> @@ -197,6 +197,12 @@ static void imx_ldb_encoder_enable(struct drm_encoder *encoder)
>  	int dual = ldb->ldb_ctrl & LDB_SPLIT_MODE_EN;
>  	int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);
> 
> +	if (mux < 0) {
> +		dev_warn(ldb->dev,
> +			 "%s: invalid mux\n", __func__);

trivia:

Any real reason to make this 2 lines?  It fits nicely in 80 chars.  Maybe:

		dev_warn(ldb->dev, "%s: invalid mux: %d\n", __func__, mux);

or maybe:

		dev_warn(ldb->dev, "%s: invalid mux: %pe\n",
			 __func__, ERR_PTR(mux));

> @@ -255,6 +261,12 @@ imx_ldb_encoder_atomic_mode_set(struct drm_encoder *encoder,
[]
> +	if (mux < 0) {
> +		dev_warn(ldb->dev,
> +			 "%s: invalid mux\n", __func__);

etc...

Re: [PATCH] drm/imx: fix out of bounds array access warning

[Liu Ying]

On Tue, 2021-03-23 at 07:19 -0700, Joe Perches wrote:
> On Tue, 2021-03-23 at 14:05 +0100, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@arndb.de>
> > 
> > When CONFIG_OF is disabled, building with 'make W=1' produces warnings
> > about out of bounds array access:
> > 
> > drivers/gpu/drm/imx/imx-ldb.c: In function 'imx_ldb_set_clock.constprop':
> > drivers/gpu/drm/imx/imx-ldb.c:186:8: error: array subscript -22 is below array bounds of 'struct clk *[4]' [-Werror=array-bounds]
> > 
> > Add an error check before the index is used, which helps with the
> > warning, as well as any possible other error condition that may be
> > triggered at runtime.
> []
> > diff --git a/drivers/gpu/drm/imx/imx-ldb.c b/drivers/gpu/drm/imx/imx-ldb.c
> []
> > @@ -197,6 +197,12 @@ static void imx_ldb_encoder_enable(struct drm_encoder *encoder)
> >  	int dual = ldb->ldb_ctrl & LDB_SPLIT_MODE_EN;
> >  	int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);
> > 
> > +	if (mux < 0) {
> > +		dev_warn(ldb->dev,
> > +			 "%s: invalid mux\n", __func__);
> 
> trivia:
> 
> Any real reason to make this 2 lines?  It fits nicely in 80 chars.  Maybe:
> 
> 		dev_warn(ldb->dev, "%s: invalid mux: %d\n", __func__, mux);
> 
> or maybe:
> 
> 		dev_warn(ldb->dev, "%s: invalid mux: %pe\n",
> 			 __func__, ERR_PTR(mux));

+1

The second one looks better as it's more informative.

Regards,
Liu Ying

> 
> > @@ -255,6 +261,12 @@ imx_ldb_encoder_atomic_mode_set(struct drm_encoder *encoder,
> []
> > +	if (mux < 0) {
> > +		dev_warn(ldb->dev,
> > +			 "%s: invalid mux\n", __func__);
> 
> etc...
> 
> 

Re: [PATCH] drm/imx: fix out of bounds array access warning

[Liu Ying]

Hi Arnd,

Thanks for your patch.

It would be good to improve the patch's head line to something like:
drm/imx: imx-ldb: fix out of bounds array access warning

Regards,
Liu Ying

On Tue, 2021-03-23 at 14:05 +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> When CONFIG_OF is disabled, building with 'make W=1' produces warnings
> about out of bounds array access:
> 
> drivers/gpu/drm/imx/imx-ldb.c: In function 'imx_ldb_set_clock.constprop':
> drivers/gpu/drm/imx/imx-ldb.c:186:8: error: array subscript -22 is below array bounds of 'struct clk *[4]' [-Werror=array-bounds]
> 
> Add an error check before the index is used, which helps with the
> warning, as well as any possible other error condition that may be
> triggered at runtime.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/gpu/drm/imx/imx-ldb.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/imx/imx-ldb.c b/drivers/gpu/drm/imx/imx-ldb.c
> index dbfe39e2f7f6..1210360cec8a 100644
> --- a/drivers/gpu/drm/imx/imx-ldb.c
> +++ b/drivers/gpu/drm/imx/imx-ldb.c
> @@ -197,6 +197,12 @@ static void imx_ldb_encoder_enable(struct drm_encoder *encoder)
>  	int dual = ldb->ldb_ctrl & LDB_SPLIT_MODE_EN;
>  	int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);
>  
> +	if (mux < 0) {
> +		dev_warn(ldb->dev,
> +			 "%s: invalid mux\n", __func__);
> +		return;
> +	}
> +
>  	drm_panel_prepare(imx_ldb_ch->panel);
>  
>  	if (dual) {
> @@ -255,6 +261,12 @@ imx_ldb_encoder_atomic_mode_set(struct drm_encoder *encoder,
>  	int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);
>  	u32 bus_format = imx_ldb_ch->bus_format;
>  
> +	if (mux < 0) {
> +		dev_warn(ldb->dev,
> +			 "%s: invalid mux\n", __func__);
> +		return;
> +	}
> +
>  	if (mode->clock > 170000) {
>  		dev_warn(ldb->dev,
>  			 "%s: mode exceeds 170 MHz pixel clock\n", __func__);