[PATCH v2] 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. Refactor to use devm_clk_get_enabled() instead.

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
Suggested-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
Cc: Daniel Palmer <daniel@xxxxxxxxx>
Cc: Romain Perier <romain.perier@xxxxxxxxx>
Cc: Alessandro Zummo <a.zummo@xxxxxxxxxxxx>
Cc: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-rtc@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
v1: https://lore.kernel.org/lkml/20221118233101.never.215-kees@xxxxxxxxxx/
v2: use devm_clk_get_enabled() (christophe)
---
 drivers/rtc/rtc-msc313.c | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

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);
-- 
2.34.1