rtc: msc313: Fix function prototype mismatch in msc313_rtc_probe()

  With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG),
indirect call targets are validated against the expected function
pointer prototype to make sure the call target is valid to help mitigate
ROP attacks. If they are not identical, there is a failure at run time,
which manifests as either a kernel panic or thread getting killed.

msc313_rtc_probe() was passing clk_disable_unprepare() directly, which
did not have matching prototypes for devm_add_action_or_reset()'s callback
argument. Add a wrapper and remove the cast.

This was found as a result of Clang's new -Wcast-function-type-strict
flag, which is more sensitive than the simpler -Wcast-function-type,
which only checks for type width mismatches.

Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/202211041527.HD8TLSE1-lkp@intel.com
Cc: Daniel Palmer <daniel@thingy.jp>
Cc: Romain Perier <romain.perier@gmail.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-rtc@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/rtc/rtc-msc313.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
  

Le 19/11/2022 à 00:31, Kees Cook a écrit :
> With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG),
> indirect call targets are validated against the expected function
> pointer prototype to make sure the call target is valid to help mitigate
> ROP attacks. If they are not identical, there is a failure at run time,
> which manifests as either a kernel panic or thread getting killed.
> 
> msc313_rtc_probe() was passing clk_disable_unprepare() directly, which
> did not have matching prototypes for devm_add_action_or_reset()'s callback
> argument. Add a wrapper and remove the cast.
> 
> This was found as a result of Clang's new -Wcast-function-type-strict
> flag, which is more sensitive than the simpler -Wcast-function-type,
> which only checks for type width mismatches.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Link: https://lore.kernel.org/lkml/202211041527.HD8TLSE1-lkp@intel.com
> Cc: Daniel Palmer <daniel@thingy.jp>
> Cc: Romain Perier <romain.perier@gmail.com>
> Cc: Alessandro Zummo <a.zummo@towertech.it>
> Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-rtc@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>   drivers/rtc/rtc-msc313.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/rtc/rtc-msc313.c b/drivers/rtc/rtc-msc313.c
> index f3fde013c4b8..36e3e77f303e 100644
> --- a/drivers/rtc/rtc-msc313.c
> +++ b/drivers/rtc/rtc-msc313.c
> @@ -177,6 +177,13 @@ static irqreturn_t msc313_rtc_interrupt(s32 irq, void *dev_id)
>   	return IRQ_HANDLED;
>   }
>   
> +static void msc313_clk_disable_unprepare(void *data)
> +{
> +	struct clk *clk = data;
> +
> +	clk_disable_unprepare(clk);
> +}
> +
>   static int msc313_rtc_probe(struct platform_device *pdev)
>   {
>   	struct device *dev = &pdev->dev;
> @@ -224,7 +231,7 @@ static int msc313_rtc_probe(struct platform_device *pdev)
>   		return ret;
>   	}
>   
> -	ret = devm_add_action_or_reset(dev, (void (*) (void *))clk_disable_unprepare, clk);
> +	ret = devm_add_action_or_reset(dev, msc313_clk_disable_unprepare, clk);
>   	if (ret)
>   		return ret;
>   

Hi,

another way to fix it, is to use devm_clk_get_enabled().

It removes some LoC instead of introducing some new ones and saves a few 
bytes of memory.

CJ
  

On Sat, Nov 19, 2022 at 09:05:28AM +0100, Christophe JAILLET wrote:
> Le 19/11/2022 à 00:31, Kees Cook a écrit :
> > With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG),
> > indirect call targets are validated against the expected function
> > pointer prototype to make sure the call target is valid to help mitigate
> > ROP attacks. If they are not identical, there is a failure at run time,
> > which manifests as either a kernel panic or thread getting killed.
> > 
> > msc313_rtc_probe() was passing clk_disable_unprepare() directly, which
> > did not have matching prototypes for devm_add_action_or_reset()'s callback
> > argument. Add a wrapper and remove the cast.
> > 
> > This was found as a result of Clang's new -Wcast-function-type-strict
> > flag, which is more sensitive than the simpler -Wcast-function-type,
> > which only checks for type width mismatches.
> > 
> > Reported-by: kernel test robot <lkp@intel.com>
> > Link: https://lore.kernel.org/lkml/202211041527.HD8TLSE1-lkp@intel.com
> > Cc: Daniel Palmer <daniel@thingy.jp>
> > Cc: Romain Perier <romain.perier@gmail.com>
> > Cc: Alessandro Zummo <a.zummo@towertech.it>
> > Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
> > Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> > Cc: linux-arm-kernel@lists.infradead.org
> > Cc: linux-rtc@vger.kernel.org
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> >   drivers/rtc/rtc-msc313.c | 9 ++++++++-
> >   1 file changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/rtc/rtc-msc313.c b/drivers/rtc/rtc-msc313.c
> > index f3fde013c4b8..36e3e77f303e 100644
> > --- a/drivers/rtc/rtc-msc313.c
> > +++ b/drivers/rtc/rtc-msc313.c
> > @@ -177,6 +177,13 @@ static irqreturn_t msc313_rtc_interrupt(s32 irq, void *dev_id)
> >   	return IRQ_HANDLED;
> >   }
> > +static void msc313_clk_disable_unprepare(void *data)
> > +{
> > +	struct clk *clk = data;
> > +
> > +	clk_disable_unprepare(clk);
> > +}
> > +
> >   static int msc313_rtc_probe(struct platform_device *pdev)
> >   {
> >   	struct device *dev = &pdev->dev;
> > @@ -224,7 +231,7 @@ static int msc313_rtc_probe(struct platform_device *pdev)
> >   		return ret;
> >   	}
> > -	ret = devm_add_action_or_reset(dev, (void (*) (void *))clk_disable_unprepare, clk);
> > +	ret = devm_add_action_or_reset(dev, msc313_clk_disable_unprepare, clk);
> >   	if (ret)
> >   		return ret;
> 
> Hi,
> 
> another way to fix it, is to use devm_clk_get_enabled().
> 
> It removes some LoC instead of introducing some new ones and saves a few
> bytes of memory.

Hrm, I'm not familiar with the clk stuff here -- how do I use it? Should
it just be like this? (The NULL argument is ok?)

diff --git a/drivers/rtc/rtc-msc313.c b/drivers/rtc/rtc-msc313.c
index f3fde013c4b8..8d7737e0e2e0 100644
--- a/drivers/rtc/rtc-msc313.c
+++ b/drivers/rtc/rtc-msc313.c
@@ -212,22 +212,12 @@ static int msc313_rtc_probe(struct platform_device *pdev)
 		return ret;
 	}
 
-	clk = devm_clk_get(dev, NULL);
+	clk = devm_clk_get_enabled(dev, NULL);
 	if (IS_ERR(clk)) {
 		dev_err(dev, "No input reference clock\n");
 		return PTR_ERR(clk);
 	}
 
-	ret = clk_prepare_enable(clk);
-	if (ret) {
-		dev_err(dev, "Failed to enable the reference clock, %d\n", ret);
-		return ret;
-	}
-
-	ret = devm_add_action_or_reset(dev, (void (*) (void *))clk_disable_unprepare, clk);
-	if (ret)
-		return ret;
-
 	rate = clk_get_rate(clk);
 	writew(rate & 0xFFFF, priv->rtc_base + REG_RTC_FREQ_CW_L);
 	writew((rate >> 16) & 0xFFFF, priv->rtc_base + REG_RTC_FREQ_CW_H);
  

Le 02/12/2022 à 05:46, Kees Cook a écrit :
> On Sat, Nov 19, 2022 at 09:05:28AM +0100, Christophe JAILLET wrote:
>> Le 19/11/2022 à 00:31, Kees Cook a écrit :
>>> With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG),
>>> indirect call targets are validated against the expected function
>>> pointer prototype to make sure the call target is valid to help mitigate
>>> ROP attacks. If they are not identical, there is a failure at run time,
>>> which manifests as either a kernel panic or thread getting killed.
>>>
>>> msc313_rtc_probe() was passing clk_disable_unprepare() directly, which
>>> did not have matching prototypes for devm_add_action_or_reset()'s callback
>>> argument. Add a wrapper and remove the cast.
>>>
>>> This was found as a result of Clang's new -Wcast-function-type-strict
>>> flag, which is more sensitive than the simpler -Wcast-function-type,
>>> which only checks for type width mismatches.
>>>
>>> Reported-by: kernel test robot <lkp@intel.com>
>>> Link: https://lore.kernel.org/lkml/202211041527.HD8TLSE1-lkp@intel.com
>>> Cc: Daniel Palmer <daniel@thingy.jp>
>>> Cc: Romain Perier <romain.perier@gmail.com>
>>> Cc: Alessandro Zummo <a.zummo@towertech.it>
>>> Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
>>> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
>>> Cc: linux-arm-kernel@lists.infradead.org
>>> Cc: linux-rtc@vger.kernel.org
>>> Signed-off-by: Kees Cook <keescook@chromium.org>
>>> ---
>>>    drivers/rtc/rtc-msc313.c | 9 ++++++++-
>>>    1 file changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/rtc/rtc-msc313.c b/drivers/rtc/rtc-msc313.c
>>> index f3fde013c4b8..36e3e77f303e 100644
>>> --- a/drivers/rtc/rtc-msc313.c
>>> +++ b/drivers/rtc/rtc-msc313.c
>>> @@ -177,6 +177,13 @@ static irqreturn_t msc313_rtc_interrupt(s32 irq, void *dev_id)
>>>    	return IRQ_HANDLED;
>>>    }
>>> +static void msc313_clk_disable_unprepare(void *data)
>>> +{
>>> +	struct clk *clk = data;
>>> +
>>> +	clk_disable_unprepare(clk);
>>> +}
>>> +
>>>    static int msc313_rtc_probe(struct platform_device *pdev)
>>>    {
>>>    	struct device *dev = &pdev->dev;
>>> @@ -224,7 +231,7 @@ static int msc313_rtc_probe(struct platform_device *pdev)
>>>    		return ret;
>>>    	}
>>> -	ret = devm_add_action_or_reset(dev, (void (*) (void *))clk_disable_unprepare, clk);
>>> +	ret = devm_add_action_or_reset(dev, msc313_clk_disable_unprepare, clk);
>>>    	if (ret)
>>>    		return ret;
>>
>> Hi,
>>
>> another way to fix it, is to use devm_clk_get_enabled().
>>
>> It removes some LoC instead of introducing some new ones and saves a few
>> bytes of memory.
> 
> Hrm, I'm not familiar with the clk stuff here -- how do I use it? Should
> it just be like this? (The NULL argument is ok?)

Yes, the code below looks fine.
NULL argument is ok.

See [1]. Both function are very similar. devm_clk_get_enabled() just 
pass some additional init() and exit() functions.

CJ


[1]: 
https://elixir.bootlin.com/linux/v6.1-rc7/source/drivers/clk/clk-devres.c#L63
> 
> diff --git a/drivers/rtc/rtc-msc313.c b/drivers/rtc/rtc-msc313.c
> index f3fde013c4b8..8d7737e0e2e0 100644
> --- a/drivers/rtc/rtc-msc313.c
> +++ b/drivers/rtc/rtc-msc313.c
> @@ -212,22 +212,12 @@ static int msc313_rtc_probe(struct platform_device *pdev)
>   		return ret;
>   	}
>   
> -	clk = devm_clk_get(dev, NULL);
> +	clk = devm_clk_get_enabled(dev, NULL);
>   	if (IS_ERR(clk)) {
>   		dev_err(dev, "No input reference clock\n");
>   		return PTR_ERR(clk);
>   	}
>   
> -	ret = clk_prepare_enable(clk);
> -	if (ret) {
> -		dev_err(dev, "Failed to enable the reference clock, %d\n", ret);
> -		return ret;
> -	}
> -
> -	ret = devm_add_action_or_reset(dev, (void (*) (void *))clk_disable_unprepare, clk);
> -	if (ret)
> -		return ret;
> -
>   	rate = clk_get_rate(clk);
>   	writew(rate & 0xFFFF, priv->rtc_base + REG_RTC_FREQ_CW_L);
>   	writew((rate >> 16) & 0xFFFF, priv->rtc_base + REG_RTC_FREQ_CW_H);
>