* [Qemu-devel] [PATCH v2] timer: a9gtimer: check auto-increment register value
@ 2016-09-28 9:16 P J P
2016-09-30 17:30 ` Peter Maydell
0 siblings, 1 reply; 5+ messages in thread
From: P J P @ 2016-09-28 9:16 UTC (permalink / raw)
To: Qemu Developers; +Cc: Peter Maydell, Li Qiang, qemu-arm, Prasad J Pandit
From: Prasad J Pandit <pjp@fedoraproject.org>
ARM A9MP processor has a peripheral timer with an auto-increment
register, which holds an increment step value. A user could set
this value to zero, when auto-increment control bit is enabled.
This leads to an infinite loop in 'a9_gtimer_update' while
updating comparator value. Remove the loop incrementing the
comparator value; Add check to avoid value zero.
Reported-by: Li Qiang <liqiang6-s@360.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
hw/timer/a9gtimer.c | 22 ++++++++++------------
1 file changed, 10 insertions(+), 12 deletions(-)
Update per
-> https://lists.gnu.org/archive/html/qemu-devel/2016-09/msg05682.html
diff --git a/hw/timer/a9gtimer.c b/hw/timer/a9gtimer.c
index 772f85f..021ae59 100644
--- a/hw/timer/a9gtimer.c
+++ b/hw/timer/a9gtimer.c
@@ -72,7 +72,7 @@ static void a9_gtimer_update(A9GTimerState *s, bool sync)
{
A9GTimerUpdate update = a9_gtimer_get_update(s);
- int i;
+ uint32_t i, inc;
int64_t next_cdiff = 0;
for (i = 0; i < s->num_cpu; ++i) {
@@ -82,16 +82,14 @@ static void a9_gtimer_update(A9GTimerState *s, bool sync)
if ((s->control & R_CONTROL_TIMER_ENABLE) &&
(gtb->control & R_CONTROL_COMP_ENABLE)) {
/* R2p0+, where the compare function is >= */
- while (gtb->compare < update.new) {
- DB_PRINT("Compare event happened for CPU %d\n", i);
- gtb->status = 1;
- if (gtb->control & R_CONTROL_AUTO_INCREMENT) {
- DB_PRINT("Auto incrementing timer compare by %" PRId32 "\n",
- gtb->inc);
- gtb->compare += gtb->inc;
- } else {
- break;
- }
+ DB_PRINT("Compare event happened for CPU %d\n", i);
+ gtb->status = 1;
+ if (gtb->control & R_CONTROL_AUTO_INCREMENT
+ && gtb->compare < update.new) {
+ inc = ((update.new - gtb->compare - 1) / gtb->inc) * gtb->inc;
+ DB_PRINT("Auto incrementing timer compare by %"
+ PRId32 "\n", inc);
+ gtb->compare += inc;
}
cdiff = (int64_t)gtb->compare - (int64_t)update.new + 1;
if (cdiff > 0 && (cdiff < next_cdiff || !next_cdiff)) {
@@ -210,7 +208,7 @@ static void a9_gtimer_write(void *opaque, hwaddr addr, uint64_t value,
gtb->compare = deposit64(gtb->compare, shift, 32, value);
break;
case R_AUTO_INCREMENT:
- gtb->inc = value;
+ gtb->inc = value ? value : 1;
return;
default:
return;
--
2.5.5
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [Qemu-devel] [PATCH v2] timer: a9gtimer: check auto-increment register value
2016-09-28 9:16 [Qemu-devel] [PATCH v2] timer: a9gtimer: check auto-increment register value P J P
@ 2016-09-30 17:30 ` Peter Maydell
2016-10-02 6:15 ` P J P
0 siblings, 1 reply; 5+ messages in thread
From: Peter Maydell @ 2016-09-30 17:30 UTC (permalink / raw)
To: P J P; +Cc: Qemu Developers, Li Qiang, qemu-arm, Prasad J Pandit
On 28 September 2016 at 02:16, P J P <ppandit@redhat.com> wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> ARM A9MP processor has a peripheral timer with an auto-increment
> register, which holds an increment step value. A user could set
> this value to zero, when auto-increment control bit is enabled.
> This leads to an infinite loop in 'a9_gtimer_update' while
> updating comparator value. Remove the loop incrementing the
> comparator value; Add check to avoid value zero.
>
> Reported-by: Li Qiang <liqiang6-s@360.cn>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
> hw/timer/a9gtimer.c | 22 ++++++++++------------
> 1 file changed, 10 insertions(+), 12 deletions(-)
>
> Update per
> -> https://lists.gnu.org/archive/html/qemu-devel/2016-09/msg05682.html
>
> diff --git a/hw/timer/a9gtimer.c b/hw/timer/a9gtimer.c
> index 772f85f..021ae59 100644
> --- a/hw/timer/a9gtimer.c
> +++ b/hw/timer/a9gtimer.c
> @@ -72,7 +72,7 @@ static void a9_gtimer_update(A9GTimerState *s, bool sync)
> {
>
> A9GTimerUpdate update = a9_gtimer_get_update(s);
> - int i;
> + uint32_t i, inc;
Why have you changed the type of i when you haven't changed
any of the code that works with it?
Since the gtb->compare field is 64 bit your inc variable should
probably be uint64_t.
> int64_t next_cdiff = 0;
>
> for (i = 0; i < s->num_cpu; ++i) {
> @@ -82,16 +82,14 @@ static void a9_gtimer_update(A9GTimerState *s, bool sync)
> if ((s->control & R_CONTROL_TIMER_ENABLE) &&
> (gtb->control & R_CONTROL_COMP_ENABLE)) {
> /* R2p0+, where the compare function is >= */
> - while (gtb->compare < update.new) {
> - DB_PRINT("Compare event happened for CPU %d\n", i);
> - gtb->status = 1;
> - if (gtb->control & R_CONTROL_AUTO_INCREMENT) {
> - DB_PRINT("Auto incrementing timer compare by %" PRId32 "\n",
> - gtb->inc);
> - gtb->compare += gtb->inc;
> - } else {
> - break;
> - }
> + DB_PRINT("Compare event happened for CPU %d\n", i);
This is wrong -- this debug print should only happen when the
comparator matches (ie when gtb->compare is less than update.new),
not every time.
> + gtb->status = 1;
Similarly the status flag should only be set when the comparator
matches.
> + if (gtb->control & R_CONTROL_AUTO_INCREMENT
> + && gtb->compare < update.new) {
> + inc = ((update.new - gtb->compare - 1) / gtb->inc) * gtb->inc;
I suggest using either QEMU_ALIGN_UP or QEMU_ALIGN_DOWN here,
depending on which way round you're trying for.
Also this will divide by zero if gtb->inc is 0 (as for instance
it will be on reset).
> + DB_PRINT("Auto incrementing timer compare by %"
> + PRId32 "\n", inc);
> + gtb->compare += inc;
> }
> cdiff = (int64_t)gtb->compare - (int64_t)update.new + 1;
> if (cdiff > 0 && (cdiff < next_cdiff || !next_cdiff)) {
> @@ -210,7 +208,7 @@ static void a9_gtimer_write(void *opaque, hwaddr addr, uint64_t value,
> gtb->compare = deposit64(gtb->compare, shift, 32, value);
> break;
> case R_AUTO_INCREMENT:
> - gtb->inc = value;
> + gtb->inc = value ? value : 1;
Where has this change come from ??
> return;
> default:
> return;
> --
> 2.5.5
>
thanks
-- PMM
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [Qemu-devel] [PATCH v2] timer: a9gtimer: check auto-increment register value
2016-09-30 17:30 ` Peter Maydell
@ 2016-10-02 6:15 ` P J P
2016-10-02 14:58 ` Peter Maydell
0 siblings, 1 reply; 5+ messages in thread
From: P J P @ 2016-10-02 6:15 UTC (permalink / raw)
To: Peter Maydell; +Cc: Qemu Developers, Li Qiang, qemu-arm
Hello Peter,
+-- On Fri, 30 Sep 2016, Peter Maydell wrote --+
| > - int i;
| > + uint32_t i, inc;
|
| Why have you changed the type of i when you haven't changed
| any of the code that works with it?
Actually I declared 'inc' on the same line, then changed type to 'uint32' as
'gtb->inc' is of the same type.
| Since the gtb->compare field is 64 bit your inc variable should
| probably be uint64_t.
Okay. I was wondering about its values, as gtb->inc is 'uint32_t' type.
| > + DB_PRINT("Compare event happened for CPU %d\n", i);
|
| This is wrong -- this debug print should only happen when the
| comparator matches (ie when gtb->compare is less than update.new),
| not every time.
|
| > + gtb->status = 1;
|
| Similarly the status flag should only be set when the comparator
| matches.
|
| > + if (gtb->control & R_CONTROL_AUTO_INCREMENT
| > + && gtb->compare < update.new) {
| > + inc = ((update.new - gtb->compare - 1) / gtb->inc) * gtb->inc;
|
| I suggest using either QEMU_ALIGN_UP or QEMU_ALIGN_DOWN here,
| depending on which way round you're trying for.
Okay.
| Also this will divide by zero if gtb->inc is 0 (as for instance
| it will be on reset).
|
| > + gtb->inc = value ? value : 1;
|
| Where has this change come from ??
This was to avoid the possible divide by zero. Couldn't find if zero could
be valid value for 'gtb->inc' and a non-zero default value if not. If
'gtb->inc' could be zero, should the 'gtb->compare += inc' only happen when
it's non-zero ? Ie gtb->status would be set if gtb->inc > 0.
Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [Qemu-devel] [PATCH v2] timer: a9gtimer: check auto-increment register value
2016-10-02 6:15 ` P J P
@ 2016-10-02 14:58 ` Peter Maydell
2016-10-03 9:13 ` P J P
0 siblings, 1 reply; 5+ messages in thread
From: Peter Maydell @ 2016-10-02 14:58 UTC (permalink / raw)
To: P J P; +Cc: Qemu Developers, Li Qiang, qemu-arm
On 1 October 2016 at 23:15, P J P <ppandit@redhat.com> wrote:
> Hello Peter,
>
> +-- On Fri, 30 Sep 2016, Peter Maydell wrote --+
> | Since the gtb->compare field is 64 bit your inc variable should
> | probably be uint64_t.
>
> Okay. I was wondering about its values, as gtb->inc is 'uint32_t' type.
The timer can't autoincrement by more than a 32 bit value, but
the timer value is 64 bits, and since this code may be doing more than
one autoincrement it's better to use 64 bits.
> | > + DB_PRINT("Compare event happened for CPU %d\n", i);
> |
> | This is wrong -- this debug print should only happen when the
> | comparator matches (ie when gtb->compare is less than update.new),
> | not every time.
> |
> | > + gtb->status = 1;
> |
> | Similarly the status flag should only be set when the comparator
> | matches.
> |
> | > + if (gtb->control & R_CONTROL_AUTO_INCREMENT
> | > + && gtb->compare < update.new) {
> | > + inc = ((update.new - gtb->compare - 1) / gtb->inc) * gtb->inc;
> |
> | I suggest using either QEMU_ALIGN_UP or QEMU_ALIGN_DOWN here,
> | depending on which way round you're trying for.
>
> Okay.
>
> | Also this will divide by zero if gtb->inc is 0 (as for instance
> | it will be on reset).
> |
> | > + gtb->inc = value ? value : 1;
> |
> | Where has this change come from ??
>
> This was to avoid the possible divide by zero. Couldn't find if zero could
> be valid value for 'gtb->inc' and a non-zero default value if not.
If in doubt, you need to check the datasheet/technical reference
manual for the hardware, in this case
http://infocenter.arm.com/help/topic/com.arm.doc.100486_0401_10_en/ada1443777319205.html
Zero is a valid value for the auto-increment register,
and in fact it is the documented reset value.
> If
> 'gtb->inc' could be zero, should the 'gtb->compare += inc'
> only happen when
> it's non-zero ? Ie gtb->status would be set if gtb->inc > 0.
If gtb->inc is zero, then when the timer fires
the compare register should increment by the increment value
(which will be zero, so it won't change). This is not a
particularly useful setting for the guest to put the timer
into, but the behaviour is well-defined. (Effectively, setting
the increment to 0 is equivalent to disabling auto-increment.)
gtb->status should be set whenever the timer comparator
fires, whether we are auto-incrementing or not, and
whatever the value of the auto-increment register is.
It is the "timer matched" interrupt output. (Your current
patch is wrong in that it has moved setting gtb->status
into the wrong place, as I mentioned above.)
thanks
-- PMM
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [Qemu-devel] [PATCH v2] timer: a9gtimer: check auto-increment register value
2016-10-02 14:58 ` Peter Maydell
@ 2016-10-03 9:13 ` P J P
0 siblings, 0 replies; 5+ messages in thread
From: P J P @ 2016-10-03 9:13 UTC (permalink / raw)
To: Peter Maydell; +Cc: Qemu Developers, qemu-arm, Li Qiang
Hello Peter,
+-- On Sun, 2 Oct 2016, Peter Maydell wrote --+
| The timer can't autoincrement by more than a 32 bit value, but
| the timer value is 64 bits, and since this code may be doing more than
| one autoincrement it's better to use 64 bits.
Okay.
| If in doubt, you need to check the datasheet/technical reference manual for
| the hardware, in this case
| http://infocenter.arm.com/help/topic/com.arm.doc.100486_0401_10_en/ada1443777319205.html
| Zero is a valid value for the auto-increment register, and in fact it is the
| documented reset value.
Yes, I was following the same. It does mention zero as a valid reset value,
but does not mention about value to be writen to Timer Load Register. As in,
when user attempts to write to a register.
| gtb->status should be set whenever the timer comparator
| fires, whether we are auto-incrementing or not, and
| whatever the value of the auto-increment register is.
| It is the "timer matched" interrupt output. (Your current
| patch is wrong in that it has moved setting gtb->status
| into the wrong place, as I mentioned above.)
Done; I've sent a revised patch v3.
Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F
^ permalink raw reply [flat|nested] 5+ messages in thread
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2016-09-28 9:16 [Qemu-devel] [PATCH v2] timer: a9gtimer: check auto-increment register value P J P
2016-09-30 17:30 ` Peter Maydell
2016-10-02 6:15 ` P J P
2016-10-02 14:58 ` Peter Maydell
2016-10-03 9:13 ` P J P
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