linux-kernel - [PATCH v4 19/30] stackleack: Mark stack_erasing

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Message-ID: <20250114175143.81438-20-vschneid@redhat.com>
Date: Tue, 14 Jan 2025 18:51:32 +0100
From: Valentin Schneider <vschneid@...hat.com>
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Cc: Josh Poimboeuf <jpoimboe@...nel.org>,
	Juergen Gross <jgross@...e.com>,
	Ajay Kaher <ajay.kaher@...adcom.com>,
	Alexey Makhalov <alexey.amakhalov@...adcom.com>,
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Subject: [PATCH v4 19/30] stackleack: Mark stack_erasing_bypass key as allowed in .noinstr

Later commits will cause objtool to warn about static keys being used in
.noinstr sections in order to safely defer instruction patching IPIs
targeted at NOHZ_FULL CPUs.

stack_erasing_bypass is used in .noinstr code, and can be modified at runtime
(proc/sys/kernel/stack_erasing write). However it is not expected that it
will be  flipped during latency-sensitive operations, and thus shouldn't be
a source of interference wrt the text patching IPI.

Mark it to let objtool know not to warn about it.

Reported-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Valentin Schneider <vschneid@...hat.com>
---
 kernel/stackleak.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/stackleak.c b/kernel/stackleak.c
index 39fd620a7db6f..a4f07fbc13f61 100644
--- a/kernel/stackleak.c
+++ b/kernel/stackleak.c
@@ -18,7 +18,11 @@
 #include <linux/sysctl.h>
 #include <linux/init.h>
 
-static DEFINE_STATIC_KEY_FALSE(stack_erasing_bypass);
+/*
+ * This static key can only be modified via its sysctl interface. It is
+ * expected it will remain stable during latency-senstive operations.
+ */
+static DEFINE_STATIC_KEY_FALSE_NOINSTR(stack_erasing_bypass);
 
 #ifdef CONFIG_SYSCTL
 static int stack_erasing_sysctl(const struct ctl_table *table, int write,
-- 
2.43.0