motorhead/qemu
1
0
Fork 0
mirror of https://github.com/Motorhead1991/qemu.git synced 2025-08-07 01:33:56 -06:00
Code Issues Projects Releases Packages Wiki Activity Actions

rtc: Only call rtc_set_cmos when Register B SET flag is disabled.

Browse source 
This bug occurs when the SET flag of Register B is enabled. When an RTC
data register (i.e. any of the ten time/calender CMOS bytes) is set, the
data is (as expected) correctly stored in the cmos_data array. However,
since the SET flag is enabled, the function rtc_set_time is not invoked.
As a result, the field base_rtc in RTCState remains uninitialized. This
causes a problem on subsequent writes which can end up overwriting data.
To see this, consider writing data to Register A after having written
data to any of the RTC data registers; the following figure illustrates
the call stack for the Register A write operation:

 +- cmos_io_port_write
 +-- check_update_timer
 +---- get_next_alarm
 +------ rtc_update_time

In rtc_update_time, get_guest_rtc calculates the wrong time and
overwrites the previously written RTC data register values.

Signed-off-by: Alex Horn <alex.horn@cs.ox.ac.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Alex Horn 2012-11-26 17:32:54 +01:00 • committed by Anthony Liguori
parent 03a36f17d7
commit 02c6ccc6dd
2 changed files with 45 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

6
hw/mc146818rtc.c
View file

@ -570,7 +570,11 @@ static void rtc_update_time(RTCState *s)
guest_nsec = get_guest_rtc_ns(s);
guest_sec = guest_nsec / NSEC_PER_SEC;
gmtime_r(&guest_sec, &ret);
rtc_set_cmos(s, &ret);
/* Is SET flag of Register B disabled? */
if ((s->cmos_data[RTC_REG_B] & REG_B_SET) == 0) {
rtc_set_cmos(s, &ret);
}
}
static int update_in_progress(RTCState *s)