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Mon, 26 Oct 2026 23:36:12 -0700 (PDT) Received: from localhost ([116.86.153.182]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ae40614daasm2254704a91.4.2026.10.26.23.36.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Oct 2026 23:36:12 -0700 (PDT) Date: Tue, 27 Oct 2026 14:36:09 +0800 From: Chris Down To: Peter Zijlstra , Ingo Molnar , Kees Cook Cc: Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Ard Biesheuvel , Will Deacon , Sami Tolvanen , Jonathan Corbet , Shuah Khan , Randy Dunlap , Arnd Bergmann , Greg Kroah-Hartman , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , linux-arm-kernel@lists.infradead.org, linux-riscv@lists.infradead.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: [PATCH 1/3] sched/core: Skip the shadow stack end check when SCS is disabled Message-ID: <0e607d3aa7c2c4cc1b5b8ba7b0e25ebdb55726af.1793082868.git.chris@chrisdown.name> References: X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.3.3 (9073d26d) (2026-06-12) With CONFIG_DYNAMIC_SCS, shadow call stacks are only used when the boot CPU lacks pointer authentication. scs_release() already checks scs_is_enabled() before it looks at the shadow stack since commit 9beccca09840 ("scs: add support for dynamic shadow call stacks"), but schedule_debug() does not. With CONFIG_SCHED_STACK_END_CHECK=y it therefore checks init_task's unused shadow stack on every context switch. That is harmless right now, but the check is redundant and costs a load from an unrelated cache line in __schedule(). So, let's guard on scs_is_enabled(). It is a static branch, and it folds to true when CONFIG_DYNAMIC_SCS is not set. Signed-off-by: Chris Down --- kernel/sched/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d7c3b43158de..fc269fd10192 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6152,7 +6152,7 @@ static inline void schedule_debug(struct task_struct *prev, bool preempt) if (task_stack_end_corrupted(prev)) panic("corrupted stack end detected inside scheduler\n"); - if (task_scs_end_corrupted(prev)) + if (scs_is_enabled() && task_scs_end_corrupted(prev)) panic("corrupted shadow stack detected inside scheduler\n"); #endif -- 2.54.0