2020-08-13 05:45:33

by Victor Ding

Subject: [PATCH] rtc: cmos: initialize rtc time when reading alarm

cmos_read_alarm() may leave certain fields of a struct rtc_time
untouched; therefore, these fields contain garbage if not properly
initialized, leading to inconsistent values when converting into
time64_t.
This patch to set all fields of a struct rtc_time to -1 before calling
cmos_read_alarm().

Signed-off-by: Victor Ding <[email protected]>
---

drivers/rtc/rtc-cmos.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index bcc96ab7793f..c99af567780d 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -1006,6 +1006,7 @@ static int cmos_suspend(struct device *dev)
enable_irq_wake(cmos->irq);
}

+ memset(&cmos->saved_wkalrm.time, -1, sizeof(struct rtc_time));
cmos_read_alarm(dev, &cmos->saved_wkalrm);

dev_dbg(dev, "suspend%s, ctrl %02x\n",
@@ -1054,6 +1055,7 @@ static void cmos_check_wkalrm(struct device *dev)
return;
}

+ memset(&current_alarm.time, -1, sizeof(struct rtc_time));
cmos_read_alarm(dev, &current_alarm);
t_current_expires = rtc_tm_to_time64(&current_alarm.time);
t_saved_expires = rtc_tm_to_time64(&cmos->saved_wkalrm.time);
--
2.28.0.236.gb10cc79966-goog

2020-08-13 07:34:23

by Alexandre Belloni

Subject: Re: [PATCH] rtc: cmos: initialize rtc time when reading alarm

Hi,

On 13/08/2020 15:41:34+1000, Victor Ding wrote:
> cmos_read_alarm() may leave certain fields of a struct rtc_time
> untouched; therefore, these fields contain garbage if not properly
> initialized, leading to inconsistent values when converting into
> time64_t.
> This patch to set all fields of a struct rtc_time to -1 before calling
> cmos_read_alarm().
>

I don't think this actually helps with the conversion as mktime64
is taking unsigned int so I would think you need the whole logic that is
in __rtc_read_alarm

> Signed-off-by: Victor Ding <[email protected]>
> ---
>
> drivers/rtc/rtc-cmos.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
> index bcc96ab7793f..c99af567780d 100644
> --- a/drivers/rtc/rtc-cmos.c
> +++ b/drivers/rtc/rtc-cmos.c
> @@ -1006,6 +1006,7 @@ static int cmos_suspend(struct device *dev)
> enable_irq_wake(cmos->irq);
> }
>
> + memset(&cmos->saved_wkalrm.time, -1, sizeof(struct rtc_time));
> cmos_read_alarm(dev, &cmos->saved_wkalrm);
>
> dev_dbg(dev, "suspend%s, ctrl %02x\n",
> @@ -1054,6 +1055,7 @@ static void cmos_check_wkalrm(struct device *dev)
> return;
> }
>
> + memset(&current_alarm.time, -1, sizeof(struct rtc_time));
> cmos_read_alarm(dev, &current_alarm);
> t_current_expires = rtc_tm_to_time64(&current_alarm.time);
> t_saved_expires = rtc_tm_to_time64(&cmos->saved_wkalrm.time);
> --
> 2.28.0.236.gb10cc79966-goog
>

--
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

2020-08-14 06:11:49

by Victor Ding

Subject: Re: [PATCH] rtc: cmos: initialize rtc time when reading alarm

Hi Alexandre,

On Thu, Aug 13, 2020 at 5:33 PM Alexandre Belloni
<[email protected]> wrote:
>
> Hi,
>
> On 13/08/2020 15:41:34+1000, Victor Ding wrote:
> > cmos_read_alarm() may leave certain fields of a struct rtc_time
> > untouched; therefore, these fields contain garbage if not properly
> > initialized, leading to inconsistent values when converting into
> > time64_t.
> > This patch to set all fields of a struct rtc_time to -1 before calling
> > cmos_read_alarm().
> >
>
> I don't think this actually helps with the conversion as mktime64
> is taking unsigned int so I would think you need the whole logic that is
> in __rtc_read_alarm

It's true that this change does not produce a correct time64_t; however,
it isn't the intention either. The proposed change only produces a
consistent value: calling obtaining identical struct rtc_time if the CMOS
wakealarm is unchanged. In the case of suspend/resume, a correct value
time64_t is not necessary; a consistent value is sufficient to correctly
perform an equality test for `t_current_expires` and `t_saved_expires`.
Logic to deduce a correct time64_t is expensive and hence I would like to
avoid __rtc_read_alarm's logic here.

Prior to this patch, the struct rtc_time is uninitialized. After calling
cmos_read_alarm(), the tm_year field is always left untouched and hence
contains only garbage. On platforms without enhanced RTC timers, the
tm_mon and tm_mday fields are left with garbage as well. Therefore,
`t_current_expires` and `t_saved_expires` from garbage data, which leads
to incorrect equality test results.

>
> > Signed-off-by: Victor Ding <[email protected]>
> > ---
> >
> > drivers/rtc/rtc-cmos.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
> > index bcc96ab7793f..c99af567780d 100644
> > --- a/drivers/rtc/rtc-cmos.c
> > +++ b/drivers/rtc/rtc-cmos.c
> > @@ -1006,6 +1006,7 @@ static int cmos_suspend(struct device *dev)
> > enable_irq_wake(cmos->irq);
> > }
> >
> > + memset(&cmos->saved_wkalrm.time, -1, sizeof(struct rtc_time));
> > cmos_read_alarm(dev, &cmos->saved_wkalrm);
> >
> > dev_dbg(dev, "suspend%s, ctrl %02x\n",
> > @@ -1054,6 +1055,7 @@ static void cmos_check_wkalrm(struct device *dev)
> > return;
> > }
> >
> > + memset(&current_alarm.time, -1, sizeof(struct rtc_time));
> > cmos_read_alarm(dev, &current_alarm);
> > t_current_expires = rtc_tm_to_time64(&current_alarm.time);
> > t_saved_expires = rtc_tm_to_time64(&cmos->saved_wkalrm.time);
> > --
> > 2.28.0.236.gb10cc79966-goog
> >
>
> --
> Alexandre Belloni, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com

Best regards,
Victor Ding

2020-08-14 08:58:55

by Victor Ding

Subject: Re: [PATCH] rtc: cmos: initialize rtc time when reading alarm

Hi Alexandre,

On Fri, Aug 14, 2020 at 6:15 PM Alexandre Belloni
<[email protected]> wrote:
>
> On 14/08/2020 16:10:13+1000, Victor Ding wrote:
> > Hi Alexandre,
> >
> > On Thu, Aug 13, 2020 at 5:33 PM Alexandre Belloni
> > <[email protected]> wrote:
> > >
> > > Hi,
> > >
> > > On 13/08/2020 15:41:34+1000, Victor Ding wrote:
> > > > cmos_read_alarm() may leave certain fields of a struct rtc_time
> > > > untouched; therefore, these fields contain garbage if not properly
> > > > initialized, leading to inconsistent values when converting into
> > > > time64_t.
> > > > This patch to set all fields of a struct rtc_time to -1 before calling
> > > > cmos_read_alarm().
> > > >
> > >
> > > I don't think this actually helps with the conversion as mktime64
> > > is taking unsigned int so I would think you need the whole logic that is
> > > in __rtc_read_alarm
> >
> > It's true that this change does not produce a correct time64_t; however,
> > it isn't the intention either. The proposed change only produces a
> > consistent value: calling obtaining identical struct rtc_time if the CMOS
> > wakealarm is unchanged. In the case of suspend/resume, a correct value
> > time64_t is not necessary; a consistent value is sufficient to correctly
> > perform an equality test for `t_current_expires` and `t_saved_expires`.
> > Logic to deduce a correct time64_t is expensive and hence I would like to
> > avoid __rtc_read_alarm's logic here.
> >
> > Prior to this patch, the struct rtc_time is uninitialized. After calling
> > cmos_read_alarm(), the tm_year field is always left untouched and hence
> > contains only garbage. On platforms without enhanced RTC timers, the
> > tm_mon and tm_mday fields are left with garbage as well. Therefore,
> > `t_current_expires` and `t_saved_expires` from garbage data, which leads
> > to incorrect equality test results.
> >
>
> Seeing that saved_wkalrm is initialized to zero, wouldn't it be
> sufficient to initialize current_alarm to 0? This can be done simply at
> the declaration. I personally find the -1 to be confusing especially
> since the result ends up being architecture dependent.
>

Good point. Initializing the struct to 0 is also sufficient; I'll
update the patch
to initialize the fields to 0 and submit the updated version.

Note that both `saved_wkalrm` and `current_alarm` must be initialized.
`cmos_suspend` may be called multiple times; `cmos_read_alarm` may or
may not update `time.tm_mon` or `time.tm_mday` depends on `cmos->day_alrm`
and `cmos->mon_alrm`. Both `day_alrm` and `mon_alrm` could theoretically
change. Say if at first `day_alrm` is enabled, `cmos_read_alarm` would fill
`time.tm_mday`. Later on, if `day_alrm` becomes disabled, `cmos_read_alarm`
would not update `time.tm_mday` and hence leaves its value as garbage.

> > >
> > > > Signed-off-by: Victor Ding <[email protected]>
> > > > ---
> > > >
> > > > drivers/rtc/rtc-cmos.c | 2 ++
> > > > 1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
> > > > index bcc96ab7793f..c99af567780d 100644
> > > > --- a/drivers/rtc/rtc-cmos.c
> > > > +++ b/drivers/rtc/rtc-cmos.c
> > > > @@ -1006,6 +1006,7 @@ static int cmos_suspend(struct device *dev)
> > > > enable_irq_wake(cmos->irq);
> > > > }
> > > >
> > > > + memset(&cmos->saved_wkalrm.time, -1, sizeof(struct rtc_time));
> > > > cmos_read_alarm(dev, &cmos->saved_wkalrm);
> > > >
> > > > dev_dbg(dev, "suspend%s, ctrl %02x\n",
> > > > @@ -1054,6 +1055,7 @@ static void cmos_check_wkalrm(struct device *dev)
> > > > return;
> > > > }
> > > >
> > > > + memset(&current_alarm.time, -1, sizeof(struct rtc_time));
> > > > cmos_read_alarm(dev, &current_alarm);
> > > > t_current_expires = rtc_tm_to_time64(&current_alarm.time);
> > > > t_saved_expires = rtc_tm_to_time64(&cmos->saved_wkalrm.time);
> > > > --
> > > > 2.28.0.236.gb10cc79966-goog
> > > >
> > >
> > > --
> > > Alexandre Belloni, Bootlin
> > > Embedded Linux and Kernel engineering
> > > https://bootlin.com
> >
> > Best regards,
> > Victor Ding
>
> --
> Alexandre Belloni, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com

Best regards,
Victor Ding

2020-08-14 09:29:09

by Alexandre Belloni

Subject: Re: [PATCH] rtc: cmos: initialize rtc time when reading alarm

On 14/08/2020 16:10:13+1000, Victor Ding wrote:
> Hi Alexandre,
>
> On Thu, Aug 13, 2020 at 5:33 PM Alexandre Belloni
> <[email protected]> wrote:
> >
> > Hi,
> >
> > On 13/08/2020 15:41:34+1000, Victor Ding wrote:
> > > cmos_read_alarm() may leave certain fields of a struct rtc_time
> > > untouched; therefore, these fields contain garbage if not properly
> > > initialized, leading to inconsistent values when converting into
> > > time64_t.
> > > This patch to set all fields of a struct rtc_time to -1 before calling
> > > cmos_read_alarm().
> > >
> >
> > I don't think this actually helps with the conversion as mktime64
> > is taking unsigned int so I would think you need the whole logic that is
> > in __rtc_read_alarm
>
> It's true that this change does not produce a correct time64_t; however,
> it isn't the intention either. The proposed change only produces a
> consistent value: calling obtaining identical struct rtc_time if the CMOS
> wakealarm is unchanged. In the case of suspend/resume, a correct value
> time64_t is not necessary; a consistent value is sufficient to correctly
> perform an equality test for `t_current_expires` and `t_saved_expires`.
> Logic to deduce a correct time64_t is expensive and hence I would like to
> avoid __rtc_read_alarm's logic here.
>
> Prior to this patch, the struct rtc_time is uninitialized. After calling
> cmos_read_alarm(), the tm_year field is always left untouched and hence
> contains only garbage. On platforms without enhanced RTC timers, the
> tm_mon and tm_mday fields are left with garbage as well. Therefore,
> `t_current_expires` and `t_saved_expires` from garbage data, which leads
> to incorrect equality test results.
>

Seeing that saved_wkalrm is initialized to zero, wouldn't it be
sufficient to initialize current_alarm to 0? This can be done simply at
the declaration. I personally find the -1 to be confusing especially
since the result ends up being architecture dependent.

> >
> > > Signed-off-by: Victor Ding <[email protected]>
> > > ---
> > >
> > > drivers/rtc/rtc-cmos.c | 2 ++
> > > 1 file changed, 2 insertions(+)
> > >
> > > diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
> > > index bcc96ab7793f..c99af567780d 100644
> > > --- a/drivers/rtc/rtc-cmos.c
> > > +++ b/drivers/rtc/rtc-cmos.c
> > > @@ -1006,6 +1006,7 @@ static int cmos_suspend(struct device *dev)
> > > enable_irq_wake(cmos->irq);
> > > }
> > >
> > > + memset(&cmos->saved_wkalrm.time, -1, sizeof(struct rtc_time));
> > > cmos_read_alarm(dev, &cmos->saved_wkalrm);
> > >
> > > dev_dbg(dev, "suspend%s, ctrl %02x\n",
> > > @@ -1054,6 +1055,7 @@ static void cmos_check_wkalrm(struct device *dev)
> > > return;
> > > }
> > >
> > > + memset(&current_alarm.time, -1, sizeof(struct rtc_time));
> > > cmos_read_alarm(dev, &current_alarm);
> > > t_current_expires = rtc_tm_to_time64(&current_alarm.time);
> > > t_saved_expires = rtc_tm_to_time64(&cmos->saved_wkalrm.time);
> > > --
> > > 2.28.0.236.gb10cc79966-goog
> > >
> >
> > --
> > Alexandre Belloni, Bootlin
> > Embedded Linux and Kernel engineering
> > https://bootlin.com
>
> Best regards,
> Victor Ding

--
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com