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

[Kees Cook]

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 at intel.com>
Link: https://lore.kernel.org/lkml/202211041527.HD8TLSE1-lkp@intel.com
Cc: Daniel Palmer <daniel at thingy.jp>
Cc: Romain Perier <romain.perier at gmail.com>
Cc: Alessandro Zummo <a.zummo at towertech.it>
Cc: Alexandre Belloni <alexandre.belloni at bootlin.com>
Cc: "Gustavo A. R. Silva" <gustavoars at kernel.org>
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-rtc at vger.kernel.org
Signed-off-by: Kees Cook <keescook at 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;
 
-- 
2.34.1