linux-kernel - [PATCH 5.14 154/169] sched/scs: Reset the shadow stack when idle_task

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Message-Id: <20211025191036.972654970@linuxfoundation.org>
Date:   Mon, 25 Oct 2021 21:15:35 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Woody Lin <woodylin@...gle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.14 154/169] sched/scs: Reset the shadow stack when idle_task_exit

From: Woody Lin <woodylin@...gle.com>

[ 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@...gle.com>
[peterz: Changelog]
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@....com>
Link: https://lore.kernel.org/r/20211012083521.973587-1-woodylin@google.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/sched/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 399c37c95392..e165d28cf73b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8495,6 +8495,7 @@ 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