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

From: Kees Cook
Date: Thu Dec 01 2022 - 23:46:58 EST


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?)

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);

--
Kees Cook