* [PATCH v3] sched: Fix out-of-bound access in uclamp
@ 2021-04-30 15:14 Quentin Perret
2021-04-30 15:27 ` Vincent Guittot
2021-05-06 13:48 ` [tip: sched/urgent] " tip-bot2 for Quentin Perret
0 siblings, 2 replies; 5+ messages in thread
From: Quentin Perret @ 2021-04-30 15:14 UTC (permalink / raw)
To: mingo, peterz, vincent.guittot, juri.lelli
Cc: dietmar.eggemann, rostedt, bsegall, mgorman, bristot,
qais.yousef, kernel-team, linux-kernel, patrick.bellasi
Util-clamp places tasks in different buckets based on their clamp values
for performance reasons. However, the size of buckets is currently
computed using a rounding division, which can lead to an off-by-one
error in some configurations.
For instance, with 20 buckets, the bucket size will be 1024/20=51. A
task with a clamp of 1024 will be mapped to bucket id 1024/51=20. Sadly,
correct indexes are in range [0,19], hence leading to an out of bound
memory access.
Clamp the bucket id to fix the issue.
Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting")
Suggested-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Quentin Perret <qperret@google.com>
---
Changes in v3:
- Keep rounding div to improve fairness (Vincent)
---
kernel/sched/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 98191218d891..c12ec648423e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -928,7 +928,7 @@ DEFINE_STATIC_KEY_FALSE(sched_uclamp_used);
static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
{
- return clamp_value / UCLAMP_BUCKET_DELTA;
+ return min_t(unsigned int, clamp_value / UCLAMP_BUCKET_DELTA, UCLAMP_BUCKETS - 1);
}
static inline unsigned int uclamp_none(enum uclamp_id clamp_id)
--
2.31.1.527.g47e6f16901-goog
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v3] sched: Fix out-of-bound access in uclamp
2021-04-30 15:14 [PATCH v3] sched: Fix out-of-bound access in uclamp Quentin Perret
@ 2021-04-30 15:27 ` Vincent Guittot
2021-05-03 10:55 ` Dietmar Eggemann
2021-05-06 13:48 ` [tip: sched/urgent] " tip-bot2 for Quentin Perret
1 sibling, 1 reply; 5+ messages in thread
From: Vincent Guittot @ 2021-04-30 15:27 UTC (permalink / raw)
To: Quentin Perret
Cc: Ingo Molnar, Peter Zijlstra, Juri Lelli, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Qais Yousef, Android Kernel Team,
linux-kernel, Patrick Bellasi
On Fri, 30 Apr 2021 at 17:14, Quentin Perret <qperret@google.com> wrote:
>
> Util-clamp places tasks in different buckets based on their clamp values
> for performance reasons. However, the size of buckets is currently
> computed using a rounding division, which can lead to an off-by-one
> error in some configurations.
>
> For instance, with 20 buckets, the bucket size will be 1024/20=51. A
> task with a clamp of 1024 will be mapped to bucket id 1024/51=20. Sadly,
> correct indexes are in range [0,19], hence leading to an out of bound
> memory access.
>
> Clamp the bucket id to fix the issue.
>
> Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting")
> Suggested-by: Qais Yousef <qais.yousef@arm.com>
> Signed-off-by: Quentin Perret <qperret@google.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
> Changes in v3:
> - Keep rounding div to improve fairness (Vincent)
> ---
> kernel/sched/core.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 98191218d891..c12ec648423e 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -928,7 +928,7 @@ DEFINE_STATIC_KEY_FALSE(sched_uclamp_used);
>
> static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
> {
> - return clamp_value / UCLAMP_BUCKET_DELTA;
> + return min_t(unsigned int, clamp_value / UCLAMP_BUCKET_DELTA, UCLAMP_BUCKETS - 1);
> }
>
> static inline unsigned int uclamp_none(enum uclamp_id clamp_id)
> --
> 2.31.1.527.g47e6f16901-goog
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v3] sched: Fix out-of-bound access in uclamp
2021-04-30 15:27 ` Vincent Guittot
@ 2021-05-03 10:55 ` Dietmar Eggemann
2021-05-03 14:45 ` Peter Zijlstra
0 siblings, 1 reply; 5+ messages in thread
From: Dietmar Eggemann @ 2021-05-03 10:55 UTC (permalink / raw)
To: Vincent Guittot, Quentin Perret
Cc: Ingo Molnar, Peter Zijlstra, Juri Lelli, Steven Rostedt,
Ben Segall, Mel Gorman, Daniel Bristot de Oliveira, Qais Yousef,
Android Kernel Team, linux-kernel, Patrick Bellasi
On 30/04/2021 17:27, Vincent Guittot wrote:
> On Fri, 30 Apr 2021 at 17:14, Quentin Perret <qperret@google.com> wrote:
>>
>> Util-clamp places tasks in different buckets based on their clamp values
>> for performance reasons. However, the size of buckets is currently
>> computed using a rounding division, which can lead to an off-by-one
>> error in some configurations.
>>
>> For instance, with 20 buckets, the bucket size will be 1024/20=51. A
>> task with a clamp of 1024 will be mapped to bucket id 1024/51=20. Sadly,
>> correct indexes are in range [0,19], hence leading to an out of bound
>> memory access.
>>
>> Clamp the bucket id to fix the issue.
>>
>> Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting")
>> Suggested-by: Qais Yousef <qais.yousef@arm.com>
>> Signed-off-by: Quentin Perret <qperret@google.com>
>
> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
I forgot that config UCLAMP_BUCKETS_COUNT is in range 5 ... 20.
So the error is bound to [-2 ... 5] (13/79, 20/51). I agree that we can
live with that.
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
>> ---
>> Changes in v3:
>> - Keep rounding div to improve fairness (Vincent)
>> ---
>> kernel/sched/core.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 98191218d891..c12ec648423e 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -928,7 +928,7 @@ DEFINE_STATIC_KEY_FALSE(sched_uclamp_used);
>>
>> static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
>> {
>> - return clamp_value / UCLAMP_BUCKET_DELTA;
>> + return min_t(unsigned int, clamp_value / UCLAMP_BUCKET_DELTA, UCLAMP_BUCKETS - 1);
>> }
>>
>> static inline unsigned int uclamp_none(enum uclamp_id clamp_id)
>> --
>> 2.31.1.527.g47e6f16901-goog
>>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v3] sched: Fix out-of-bound access in uclamp
2021-05-03 10:55 ` Dietmar Eggemann
@ 2021-05-03 14:45 ` Peter Zijlstra
0 siblings, 0 replies; 5+ messages in thread
From: Peter Zijlstra @ 2021-05-03 14:45 UTC (permalink / raw)
To: Dietmar Eggemann
Cc: Vincent Guittot, Quentin Perret, Ingo Molnar, Juri Lelli,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Qais Yousef, Android Kernel Team,
linux-kernel, Patrick Bellasi
On Mon, May 03, 2021 at 12:55:34PM +0200, Dietmar Eggemann wrote:
> On 30/04/2021 17:27, Vincent Guittot wrote:
> > On Fri, 30 Apr 2021 at 17:14, Quentin Perret <qperret@google.com> wrote:
> >>
> >> Util-clamp places tasks in different buckets based on their clamp values
> >> for performance reasons. However, the size of buckets is currently
> >> computed using a rounding division, which can lead to an off-by-one
> >> error in some configurations.
> >>
> >> For instance, with 20 buckets, the bucket size will be 1024/20=51. A
> >> task with a clamp of 1024 will be mapped to bucket id 1024/51=20. Sadly,
> >> correct indexes are in range [0,19], hence leading to an out of bound
> >> memory access.
> >>
> >> Clamp the bucket id to fix the issue.
> >>
> >> Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting")
> >> Suggested-by: Qais Yousef <qais.yousef@arm.com>
> >> Signed-off-by: Quentin Perret <qperret@google.com>
> >
> > Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Thanks!
^ permalink raw reply [flat|nested] 5+ messages in thread
* [tip: sched/urgent] sched: Fix out-of-bound access in uclamp
2021-04-30 15:14 [PATCH v3] sched: Fix out-of-bound access in uclamp Quentin Perret
2021-04-30 15:27 ` Vincent Guittot
@ 2021-05-06 13:48 ` tip-bot2 for Quentin Perret
1 sibling, 0 replies; 5+ messages in thread
From: tip-bot2 for Quentin Perret @ 2021-05-06 13:48 UTC (permalink / raw)
To: linux-tip-commits
Cc: Qais Yousef, Quentin Perret, Peter Zijlstra (Intel),
Vincent Guittot, Dietmar Eggemann, x86, linux-kernel
The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: 6d2f8909a5fabb73fe2a63918117943986c39b6c
Gitweb: https://git.kernel.org/tip/6d2f8909a5fabb73fe2a63918117943986c39b6c
Author: Quentin Perret <qperret@google.com>
AuthorDate: Fri, 30 Apr 2021 15:14:12
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 06 May 2021 15:33:26 +02:00
sched: Fix out-of-bound access in uclamp
Util-clamp places tasks in different buckets based on their clamp values
for performance reasons. However, the size of buckets is currently
computed using a rounding division, which can lead to an off-by-one
error in some configurations.
For instance, with 20 buckets, the bucket size will be 1024/20=51. A
task with a clamp of 1024 will be mapped to bucket id 1024/51=20. Sadly,
correct indexes are in range [0,19], hence leading to an out of bound
memory access.
Clamp the bucket id to fix the issue.
Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting")
Suggested-by: Qais Yousef <qais.yousef@arm.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lkml.kernel.org/r/20210430151412.160913-1-qperret@google.com
---
kernel/sched/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9143163..5226cc2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -938,7 +938,7 @@ DEFINE_STATIC_KEY_FALSE(sched_uclamp_used);
static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
{
- return clamp_value / UCLAMP_BUCKET_DELTA;
+ return min_t(unsigned int, clamp_value / UCLAMP_BUCKET_DELTA, UCLAMP_BUCKETS - 1);
}
static inline unsigned int uclamp_none(enum uclamp_id clamp_id)
^ permalink raw reply related [flat|nested] 5+ messages in thread
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2021-04-30 15:14 [PATCH v3] sched: Fix out-of-bound access in uclamp Quentin Perret
2021-04-30 15:27 ` Vincent Guittot
2021-05-03 10:55 ` Dietmar Eggemann
2021-05-03 14:45 ` Peter Zijlstra
2021-05-06 13:48 ` [tip: sched/urgent] " tip-bot2 for Quentin Perret
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