drivers/pc80/mc146818rtc: Check date and time for sanity

There are cases where the RTC_VRT bit in register D stays set after a
power failure while the real date and time registers can contain rubbish
values (can happen when RTC is not buffered). If we do not detect this
invalid date and/or time here and keep it, Linux will use these bad
values for the initial timekeeper init. This in turn can lead to dates
before 1970 in user land which can break a lot assumptions.

To fix this, check date and time sanity when the RTC is initialized and
reset the values if needed.

Change-Id: I5bc600c78bab50c70372600347f63156df127012
Signed-off-by: Werner Zeh <werner.zeh@siemens.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/54914
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/drivers/pc80/rtc/mc146818rtc.c

@@ -175,6 +175,15 @@ static void wait_uip(void)
 		;
 }
 
+/* Perform a sanity check of current date and time. */
+static int cmos_date_invalid(void)
+{
+	struct rtc_time now;
+
+	rtc_get(&now);
+	return rtc_invalid(&now);
+}
+
 /*
  * If the CMOS is cleared, the rtc_reg has the invalid date. That
  * hurts some OSes. Even if we don't set USE_OPTION_TABLE, we need
@@ -190,11 +199,11 @@ void cmos_check_update_date(void)
 	year = cmos_read(RTC_CLK_YEAR);
 
 	/*
-	 * TODO: If century is 0xFF, 100% that the CMOS is cleared.
-	 * Other than that, so far rtc_year is the only entry to check
-	 * if the date is valid.
+	 * If century is 0xFF, 100% that the CMOS is cleared.
+	 * In addition, check the sanity of all values and reset the date in case of
+	 * insane values.
 	 */
-	if (century > 0x99 || year > 0x99) /* Invalid date */
+	if (century > 0x99 || year > 0x99 || cmos_date_invalid()) /* Invalid date */
 		cmos_reset_date();
 }
 

src/lib/Makefile.inc

@@ -59,6 +59,7 @@ bootblock-y += memchr.c
 bootblock-y += memcmp.c
 bootblock-y += boot_device.c
 bootblock-y += fmap.c
+bootblcok-y += rtc.c
 
 verstage-y += prog_loaders.c
 verstage-y += prog_ops.c