[tip: sched/urgent] sched/scs: Reset the shadow stack when idle_task_exit

[tip-bot2 for Woody Lin]

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     45dfb89b8f96643268449c25d7025b17de46717c
Gitweb:        https://git.kernel.org/tip/45dfb89b8f96643268449c25d7025b17de46717c
Author:        Woody Lin <woodylin@xxxxxxxxxx>
AuthorDate:    Tue, 12 Oct 2021 16:35:21 +08:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 18 Oct 2021 16:58:41 +02:00

sched/scs: Reset the shadow stack when idle_task_exit

There was a 'init_idle' that resets scs sp to base, but is removed by
f1a0a376ca0c. Without the resetting, the hot-plugging implemented by
cpu_psci_cpu_boot will use the previous scs sp as new base when starting
up a CPU core, so the usage on scs page is being stacked up until
overflow.

This only happens on idle task since __cpu_up is using idle task as the
main thread to start up a CPU core, so the overflow can be fixed by
resetting scs sp to base in 'idle_task_exit'.

Fixes: f1a0a376ca0c ("sched/core: Initialize the idle task with preemption disabled")
Signed-off-by: Woody Lin <woodylin@xxxxxxxxxx>
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
---
 kernel/sched/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1bba412..f21714e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8795,6 +8795,7 @@ 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 */
 }