[PATCH 5.10 83/95] sched/scs: Reset the shadow stack when idle_task_exit

[Greg Kroah-Hartman]

From: Woody Lin <woodylin@xxxxxxxxxx>

[ Upstream commit 63acd42c0d4942f74710b11c38602fb14dea7320 ]

Commit f1a0a376ca0c ("sched/core: Initialize the idle task with
preemption disabled") removed the init_idle() call from
idle_thread_get(). This was the sole call-path on hotplug that resets
the Shadow Call Stack (scs) Stack Pointer (sp).

Not resetting the scs-sp leads to scs overflow after enough hotplug
cycles. Therefore add an explicit scs_task_reset() to the hotplug code
to make sure the scs-sp does get reset on hotplug.

Fixes: f1a0a376ca0c ("sched/core: Initialize the idle task with preemption disabled")
Signed-off-by: Woody Lin <woodylin@xxxxxxxxxx>
[peterz: Changelog]
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Link: https://lore.kernel.org/r/20211012083521.973587-1-woodylin@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/sched/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 6db20a66e8e6..e4551d1736fa 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6677,6 +6677,7 @@ void idle_task_exit(void)
 		finish_arch_post_lock_switch();
 	}
 
+	scs_task_reset(current);
 	/* finish_cpu(), as ran on the BP, will clean up the active_mm state */
 }
 
-- 
2.33.0