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

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Message-ID: <YNn6FqAfLwQ/Wwnu@piout.net>
Date:   Mon, 28 Jun 2021 18:34:30 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Werner Zeh <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

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?


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