linux-kernel - [PATCH] sched/scs: Reset the shadow stack when idle_task

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Date:   Tue, 12 Oct 2021 16:35:21 +0800
From:   Woody Lin <woodylin@...gle.com>
To:     Ingo Molnar <mingo@...hat.com>, Ben Segall <bsegall@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        linux-kernel@...r.kernel.org, Woody Lin <woodylin@...gle.com>
Subject: [PATCH] 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@...gle.com>
---
 kernel/sched/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1bba4128a3e6..f21714ea3db8 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 */
 }
 
-- 
2.33.0.882.g93a45727a2-goog