Re: [PATCH] rtc: msc313: Fix function prototype mismatch in msc313_rtc_probe()

[Christophe JAILLET]

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@xxxxxxxxx>
> > > Link: https://lore.kernel.org/lkml/202211041527.HD8TLSE1-lkp@xxxxxxxxx
> > > Cc: Daniel Palmer <daniel@xxxxxxxxx>
> > > Cc: Romain Perier <romain.perier@xxxxxxxxx>
> > > Cc: Alessandro Zummo <a.zummo@xxxxxxxxxxxx>
> > > Cc: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
> > > Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
> > > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > > Cc: linux-rtc@xxxxxxxxxxxxxxx
> > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > > ---
> > >    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);