* [PATCH] kcov: check kcov_softirq in kcov_remote_stop()
@ 2020-06-08 0:41 Andrey Konovalov
2020-06-08 8:05 ` Dmitry Vyukov
0 siblings, 1 reply; 2+ messages in thread
From: Andrey Konovalov @ 2020-06-08 0:41 UTC (permalink / raw)
To: Andrew Morton
Cc: linux-kernel, Dmitry Vyukov, Alexander Potapenko, Marco Elver,
Tetsuo Handa, Andrey Konovalov
kcov_remote_stop() should check that the corresponding kcov_remote_start()
actually found the specified remote handle and started collecting
coverage. This is done by checking the per thread kcov_softirq flag.
A particular failure scenario where this was observed involved a softirq
with a remote coverage collection section coming between check_kcov_mode()
and the access to t->kcov_area in __sanitizer_cov_trace_pc(). In that
softirq kcov_remote_start() bailed out after kcov_remote_find() check, but
the matching kcov_remote_stop() didn't check if kcov_remote_start()
succeeded, and overwrote per thread kcov parameters with invalid (zero)
values.
Fixes: 5ff3b30ab57d ("kcov: collect coverage from interrupts")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
kernel/kcov.c | 26 ++++++++++++++++++--------
1 file changed, 18 insertions(+), 8 deletions(-)
diff --git a/kernel/kcov.c b/kernel/kcov.c
index 55c5d883a93e..6afae0bcbac4 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -427,7 +427,8 @@ void kcov_task_exit(struct task_struct *t)
* WARN_ON(!kcov->remote && kcov->t != t);
*
* For KCOV_REMOTE_ENABLE devices, the exiting task is either:
- * 2. A remote task between kcov_remote_start() and kcov_remote_stop().
+ *
+ * 1. A remote task between kcov_remote_start() and kcov_remote_stop().
* In this case we should print a warning right away, since a task
* shouldn't be exiting when it's in a kcov coverage collection
* section. Here t points to the task that is collecting remote
@@ -437,7 +438,7 @@ void kcov_task_exit(struct task_struct *t)
* WARN_ON(kcov->remote && kcov->t != t);
*
* 2. The task that created kcov exiting without calling KCOV_DISABLE,
- * and then again we can make sure that t->kcov->t == t:
+ * and then again we make sure that t->kcov->t == t:
* WARN_ON(kcov->remote && kcov->t != t);
*
* By combining all three checks into one we get:
@@ -764,7 +765,7 @@ static const struct file_operations kcov_fops = {
* Internally, kcov_remote_start() looks up the kcov device associated with the
* provided handle, allocates an area for coverage collection, and saves the
* pointers to kcov and area into the current task_struct to allow coverage to
- * be collected via __sanitizer_cov_trace_pc()
+ * be collected via __sanitizer_cov_trace_pc().
* In turns kcov_remote_stop() clears those pointers from task_struct to stop
* collecting coverage and copies all collected coverage into the kcov area.
*/
@@ -972,16 +973,25 @@ void kcov_remote_stop(void)
local_irq_restore(flags);
return;
}
- kcov = t->kcov;
- area = t->kcov_area;
- size = t->kcov_size;
- sequence = t->kcov_sequence;
-
+ /*
+ * When in softirq, check if the corresponding kcov_remote_start()
+ * actually found the remote handle and started collecting coverage.
+ */
+ if (in_serving_softirq() && !t->kcov_softirq) {
+ local_irq_restore(flags);
+ return;
+ }
+ /* Make sure that kcov_softirq is only set when in softirq. */
if (WARN_ON(!in_serving_softirq() && t->kcov_softirq)) {
local_irq_restore(flags);
return;
}
+ kcov = t->kcov;
+ area = t->kcov_area;
+ size = t->kcov_size;
+ sequence = t->kcov_sequence;
+
kcov_stop(t);
if (in_serving_softirq()) {
t->kcov_softirq = 0;
--
2.27.0.278.ge193c7cf3a9-goog
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] kcov: check kcov_softirq in kcov_remote_stop()
2020-06-08 0:41 [PATCH] kcov: check kcov_softirq in kcov_remote_stop() Andrey Konovalov
@ 2020-06-08 8:05 ` Dmitry Vyukov
0 siblings, 0 replies; 2+ messages in thread
From: Dmitry Vyukov @ 2020-06-08 8:05 UTC (permalink / raw)
To: Andrey Konovalov
Cc: Andrew Morton, LKML, Alexander Potapenko, Marco Elver, Tetsuo Handa
On Mon, Jun 8, 2020 at 2:42 AM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> kcov_remote_stop() should check that the corresponding kcov_remote_start()
> actually found the specified remote handle and started collecting
> coverage. This is done by checking the per thread kcov_softirq flag.
>
> A particular failure scenario where this was observed involved a softirq
> with a remote coverage collection section coming between check_kcov_mode()
> and the access to t->kcov_area in __sanitizer_cov_trace_pc(). In that
> softirq kcov_remote_start() bailed out after kcov_remote_find() check, but
> the matching kcov_remote_stop() didn't check if kcov_remote_start()
> succeeded, and overwrote per thread kcov parameters with invalid (zero)
> values.
>
> Fixes: 5ff3b30ab57d ("kcov: collect coverage from interrupts")
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
> ---
> kernel/kcov.c | 26 ++++++++++++++++++--------
> 1 file changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 55c5d883a93e..6afae0bcbac4 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -427,7 +427,8 @@ void kcov_task_exit(struct task_struct *t)
> * WARN_ON(!kcov->remote && kcov->t != t);
> *
> * For KCOV_REMOTE_ENABLE devices, the exiting task is either:
> - * 2. A remote task between kcov_remote_start() and kcov_remote_stop().
> + *
> + * 1. A remote task between kcov_remote_start() and kcov_remote_stop().
> * In this case we should print a warning right away, since a task
> * shouldn't be exiting when it's in a kcov coverage collection
> * section. Here t points to the task that is collecting remote
> @@ -437,7 +438,7 @@ void kcov_task_exit(struct task_struct *t)
> * WARN_ON(kcov->remote && kcov->t != t);
> *
> * 2. The task that created kcov exiting without calling KCOV_DISABLE,
> - * and then again we can make sure that t->kcov->t == t:
> + * and then again we make sure that t->kcov->t == t:
> * WARN_ON(kcov->remote && kcov->t != t);
> *
> * By combining all three checks into one we get:
> @@ -764,7 +765,7 @@ static const struct file_operations kcov_fops = {
> * Internally, kcov_remote_start() looks up the kcov device associated with the
> * provided handle, allocates an area for coverage collection, and saves the
> * pointers to kcov and area into the current task_struct to allow coverage to
> - * be collected via __sanitizer_cov_trace_pc()
> + * be collected via __sanitizer_cov_trace_pc().
> * In turns kcov_remote_stop() clears those pointers from task_struct to stop
> * collecting coverage and copies all collected coverage into the kcov area.
> */
> @@ -972,16 +973,25 @@ void kcov_remote_stop(void)
> local_irq_restore(flags);
> return;
> }
> - kcov = t->kcov;
> - area = t->kcov_area;
> - size = t->kcov_size;
> - sequence = t->kcov_sequence;
> -
> + /*
> + * When in softirq, check if the corresponding kcov_remote_start()
> + * actually found the remote handle and started collecting coverage.
> + */
> + if (in_serving_softirq() && !t->kcov_softirq) {
> + local_irq_restore(flags);
> + return;
> + }
> + /* Make sure that kcov_softirq is only set when in softirq. */
> if (WARN_ON(!in_serving_softirq() && t->kcov_softirq)) {
> local_irq_restore(flags);
> return;
> }
>
> + kcov = t->kcov;
> + area = t->kcov_area;
> + size = t->kcov_size;
> + sequence = t->kcov_sequence;
> +
> kcov_stop(t);
> if (in_serving_softirq()) {
> t->kcov_softirq = 0;
> --
> 2.27.0.278.ge193c7cf3a9-goog
>
^ permalink raw reply [flat|nested] 2+ messages in thread
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