linux-kernel - [patch part-II V2 02/13] x86/entry: Mark enter_from_user

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Date:   Sun, 08 Mar 2020 23:24:01 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>
Subject: [patch part-II V2 02/13] x86/entry: Mark enter_from_user_mode() notrace and NOKPROBE

Both the callers in the low level ASM code and __context_tracking_exit()
which is invoked from enter_from_user_mode() via user_exit_irqoff() are
marked NOKPROBE. Allowing enter_from_user_mode() to be probed is
inconsistent at best.

Aside of that while function tracing per se is safe the function trace
entry/exit points can be used via BPF as well which is not safe to use
before context tracking has reached CONTEXT_KERNEL and adjusted RCU.

Mark it notrace and NOKROBE.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/entry/common.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -40,11 +40,12 @@

 #ifdef CONFIG_CONTEXT_TRACKING
 /* Called on entry from user mode with IRQs off. */
-__visible inline void enter_from_user_mode(void)
+__visible inline notrace void enter_from_user_mode(void)
 {
 	CT_WARN_ON(ct_state() != CONTEXT_USER);
 	user_exit_irqoff();
 }
+NOKPROBE_SYMBOL(enter_from_user_mode);
 #else
 static inline void enter_from_user_mode(void) {}
 #endif