[PATCH] rtc-cmos: take rtc_lock while accessing CMOS

[PATCH] rtc-cmos: take rtc_lock while accessing CMOS

[Mateusz Jończyk]

Reading from the CMOS involves writing to the index register and then
reading from the data register. Therefore access to the CMOS has to be
serialized with a spinlock. An invocation in cmos_set_alarm was not
serialized with rtc_lock, fix this.

Use spin_lock_irq() like the rest of the function.

Nothing in kernel modifies the RTC_DM_BINARY bit, so use a separate pair
of spin_lock_irq() / spin_unlock_irq() before doing the math.

Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: stable@vger.kernel.org
---
 drivers/rtc/rtc-cmos.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index 0fa66d1039b9..e6ff0fb7591b 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -463,7 +463,10 @@ static int cmos_set_alarm(struct device *dev, struct rtc_wkalrm *t)
 	min = t->time.tm_min;
 	sec = t->time.tm_sec;
 
+	spin_lock_irq(&rtc_lock);
 	rtc_control = CMOS_READ(RTC_CONTROL);
+	spin_unlock_irq(&rtc_lock);
+
 	if (!(rtc_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
 		/* Writing 0xff means "don't care" or "match all".  */
 		mon = (mon <= 12) ? bin2bcd(mon) : 0xff;
-- 
2.25.1

Re: [PATCH] rtc-cmos: take rtc_lock while accessing CMOS

[Nobuhiro Iwamatsu]

Hi,

2021年8月31日(火) 2:26 Mateusz Jończyk <mat.jonczyk@o2.pl>:
>
> Reading from the CMOS involves writing to the index register and then
> reading from the data register. Therefore access to the CMOS has to be
> serialized with a spinlock. An invocation in cmos_set_alarm was not
> serialized with rtc_lock, fix this.
>
> Use spin_lock_irq() like the rest of the function.
>
> Nothing in kernel modifies the RTC_DM_BINARY bit, so use a separate pair
> of spin_lock_irq() / spin_unlock_irq() before doing the math.
>
> Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
> Cc: Alessandro Zummo <a.zummo@towertech.it>
> Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
> Cc: stable@vger.kernel.org
> ---
>  drivers/rtc/rtc-cmos.c | 3 +++
>  1 file changed, 3 insertions(+)

Reviewed-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>

Best regards,
  Nobuhiro

>
> diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
> index 0fa66d1039b9..e6ff0fb7591b 100644
> --- a/drivers/rtc/rtc-cmos.c
> +++ b/drivers/rtc/rtc-cmos.c
> @@ -463,7 +463,10 @@ static int cmos_set_alarm(struct device *dev, struct rtc_wkalrm *t)
>         min = t->time.tm_min;
>         sec = t->time.tm_sec;
>
> +       spin_lock_irq(&rtc_lock);
>         rtc_control = CMOS_READ(RTC_CONTROL);
> +       spin_unlock_irq(&rtc_lock);
> +
>         if (!(rtc_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
>                 /* Writing 0xff means "don't care" or "match all".  */
>                 mon = (mon <= 12) ? bin2bcd(mon) : 0xff;
> --
> 2.25.1
>


-- 
Nobuhiro Iwamatsu
   iwamatsu at {nigauri.org / debian.org}
   GPG ID: 40AD1FA6