linux-kernel - [PATCH] x86: Use preempt_disable_notrace() in cycles_2

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20140204141315.2a968a72@gandalf.local.home>
Date:	Tue, 4 Feb 2014 14:13:15 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: [PATCH] x86: Use preempt_disable_notrace() in cycles_2_ns()

When debug preempt is enabled, preempt_disable() can be traced by
function and function graph tracing.

There's a place in the function graph tracer that calls trace_clock()
which eventually calls cycles_2_ns() outside of the recursion
protection. When cycles_2_ns() calls preempt_disable() it gets traced
and the graph tracer will go into a recursive loop causing a crash or
worse, a triple fault.

Simple fix is to use preempt_disable_notrace() in cycles_2_ns, which
makes sense because the preempt_disable() tracing may use that code
too, and it tracing it, even with recursion protection is rather
pointless.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 19e5adb..acb3b60 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -209,7 +209,7 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
 	 * dance when its actually needed.
 	 */

-	preempt_disable();
+	preempt_disable_notrace();
 	data = this_cpu_read(cyc2ns.head);
 	tail = this_cpu_read(cyc2ns.tail);

@@ -229,7 +229,7 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
 		if (!--data->__count)
 			this_cpu_write(cyc2ns.tail, data);
 	}
-	preempt_enable();
+	preempt_enable_notrace();

 	return ns;
 }
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/