linux-kernel - Re: [PATCH 1/1] x86/kernel/rtc: add sanity check for RTC date and time

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Message-ID: <YbHDSubjFrQXpfRk@piout.net>
Date:   Thu, 9 Dec 2021 09:50:18 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     "Zeh, Werner" <werner.zeh@...mens.com>
Cc:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
        "a.zummo@...ertech.it" <a.zummo@...ertech.it>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] x86/kernel/rtc: add sanity check for RTC date and
 time

Hello,

On 09/12/2021 08:05:10+0000, Zeh, Werner wrote:
> Hi Alexandre.
> 
> Is there anything more I can do for that patch in order to get some process on it?
> Or why is this patch stuck for a long time?
> 

I'm not the maintainer for that part of the kernel, I expect this to go
through the x86 tree.

> Thanks
> Werner
> 
> > -----Original Message-----
> > From: Alexandre Belloni <alexandre.belloni@...tlin.com>
> > Sent: Friday, July 2, 2021 4:11 PM
> > To: Zeh, Werner (DI MC MTS SP HW 1) <werner.zeh@...mens.com>
> > Cc: tglx@...utronix.de; mingo@...hat.com; bp@...en8.de; x86@...nel.org;
> > a.zummo@...ertech.it; linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH 1/1] x86/kernel/rtc: add sanity check for RTC date and
> > time
> >
> > On 30/06/2021 06:25:44+0000, Zeh, Werner wrote:
> > > Hi Alexandre
> > >
> > > > Hello,
> > > >
> > > > On 24/06/2021 10:15:07+0200, Werner Zeh wrote:
> > > > > The timekeeper is synchronized with the CMOS RTC when it is
> > initialized.
> > > > > If the RTC buffering is bad (not buffered at all, empty battery)
> > > > > the RTC registers can contain random data. In order to avoid date
> > > > > and time being completely rubbish check the sanity of the
> > > > > registers before calling mktime64. If the values are not valid,
> > > > > set tv_sec to 0 so that at least the starting time is valid.
> > > > >
> > > > > Signed-off-by: Werner Zeh <werner.zeh@...mens.com>
> > > > > ---
> > > > > [resent due to wrong lkml address] [added RTC maintainers to the
> > > > > recipients] This change introduces the same validity check that is
> > > > > already done in drivers/rtc/interface.c.
> > > > > If it is not done here, the timekeeper can be set up wrongly in
> > > > > the first run and won't be corrected once the RTC driver is
> > > > > started because the validity check in the RTC driver drops the
> > > > > time and date due to invalid entries.
> > > > >
> > > > >  arch/x86/kernel/rtc.c | 12 +++++++++++-
> > > > >  1 file changed, 11 insertions(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c index
> > > > > 586f718b8e95..f4af7b18c6c0 100644
> > > > > --- a/arch/x86/kernel/rtc.c
> > > > > +++ b/arch/x86/kernel/rtc.c
> > > > > @@ -9,6 +9,7 @@
> > > > >  #include <linux/export.h>
> > > > >  #include <linux/pnp.h>
> > > > >  #include <linux/of.h>
> > > > > +#include <linux/rtc.h>
> > > > >
> > > > >  #include <asm/vsyscall.h>
> > > > >  #include <asm/x86_init.h>
> > > > > @@ -64,6 +65,7 @@ void mach_get_cmos_time(struct timespec64
> > *now)
> > > > {
> > > > >         unsigned int status, year, mon, day, hour, min, sec, century = 0;
> > > > >         unsigned long flags;
> > > > > +       struct rtc_time tm = {0};
> > > > >
> > > > >         /*
> > > > >          * If pm_trace abused the RTC as storage, set the timespec to 0,
> > > > > @@
> > > > > -118,7 +120,15 @@ void mach_get_cmos_time(struct timespec64
> > *now)
> > > > >         } else
> > > > >                 year += CMOS_YEARS_OFFS;
> > > > >
> > > > > -       now->tv_sec = mktime64(year, mon, day, hour, min, sec);
> > > > > +       tm.tm_sec = sec;
> > > > > +       tm.tm_min = min;
> > > > > +       tm.tm_hour = hour;
> > > > > +       tm.tm_mday = day;
> > > > > +       tm.tm_mon = mon;
> > > > > +       tm.tm_year = year;
> > > > > +       now->tv_sec = 0;
> > > > > +       if (rtc_valid_tm(&tm) == 0)
> > > >
> > > > Doesn't that make the x86 architecture depend on CONFIG_RTC_LIB?
> > > >
> > > CONFIG_RTC_LIB is already default enabled for x86, see arch/x86/Kconfig.
> > > Do you have any other dependencies in mind I have overseen?
> > >
> >
> > Nope, everything is fine, it would be better if we could get rid of
> > mach_get_cmos_time but I don't have any clue as to why this is necessary.
> >
> >
> > --
> > Alexandre Belloni, co-owner and COO, Bootlin Embedded Linux and Kernel
> > engineering
> > https://bootlin.com/
> 

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