On Mon, Jan 30, 2023 at 10:50:01PM +0900, Akihiko Odaki wrote:
> The expiration time provided for timer_mod() can overflow if a
> ridiculously large value is set to the comparator register. The
> resulting value can represent a past time after rounded, forcing the
> timer to fire immediately. If the timer is configured as periodic, it
> will rearm the timer again, and form an endless loop.
>
> Check if the expiration value will overflow, and if it will, stop the
> timer instead of rearming the timer with the overflowed time.
>
> This bug was found by Alexander Bulekov when fuzzing igb, a new
> network device emulation:
> https://patchew.org/QEMU/20230129053316.1071513-1-alx...@bu.edu/
>
> The fixed test case is:
> fuzz/crash_2d7036941dcda1ad4380bb8a9174ed0c949bcefd
>
> Fixes: 16b29ae180 ("Add HPET emulation to qemu (Beth Kon)")
> Signed-off-by: Akihiko Odaki <akihiko.od...@daynix.com>
Acked-by: Michael S. Tsirkin <m...@redhat.com>
I'll tag this for merge.
> ---
> hw/timer/hpet.c | 19 +++++++++++++------
> 1 file changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/hw/timer/hpet.c b/hw/timer/hpet.c
> index 9520471be2..3657d5f463 100644
> --- a/hw/timer/hpet.c
> +++ b/hw/timer/hpet.c
> @@ -352,6 +352,16 @@ static const VMStateDescription vmstate_hpet = {
> }
> };
>
> +static void arm(HPETTimer *t, uint64_t ticks)
> +{
> + if (ticks < ns_to_ticks(INT64_MAX / 2)) {
> + timer_mod(t->qemu_timer,
> + qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
> ticks_to_ns(ticks));
> + } else {
> + timer_del(t->qemu_timer);
> + }
> +}
> +
> /*
> * timer expiration callback
> */
> @@ -374,13 +384,11 @@ static void hpet_timer(void *opaque)
> }
> }
> diff = hpet_calculate_diff(t, cur_tick);
> - timer_mod(t->qemu_timer,
> - qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
> (int64_t)ticks_to_ns(diff));
> + arm(t, diff);
> } else if (t->config & HPET_TN_32BIT && !timer_is_periodic(t)) {
> if (t->wrap_flag) {
> diff = hpet_calculate_diff(t, cur_tick);
> - timer_mod(t->qemu_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
> - (int64_t)ticks_to_ns(diff));
> + arm(t, diff);
> t->wrap_flag = 0;
> }
> }
> @@ -407,8 +415,7 @@ static void hpet_set_timer(HPETTimer *t)
> t->wrap_flag = 1;
> }
> }
> - timer_mod(t->qemu_timer,
> - qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
> (int64_t)ticks_to_ns(diff));
> + arm(t, diff);
> }
>
> static void hpet_del_timer(HPETTimer *t)
> --
> 2.39.1
