linux-kernel - [PATCH RT] apparmor: use a locallock instead preempt

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Date:   Mon, 16 Oct 2017 20:16:28 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-rt-users@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: [PATCH RT] apparmor: use a locallock instead preempt_disable()

get_buffers() disables preemption which acts as a lock for the per-CPU
variable. Since we can't disable preemption here on RT, a local_lock is
is used in order to remain on the same CPU and not to have more than one
user within the critical section.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 security/apparmor/include/path.h |   21 +++++++++++++++++----
 security/apparmor/lsm.c          |    2 +-
 2 files changed, 18 insertions(+), 5 deletions(-)

--- a/security/apparmor/include/path.h
+++ b/security/apparmor/include/path.h
@@ -38,9 +38,10 @@ struct aa_buffers {
 };
 
 #include <linux/percpu.h>
-#include <linux/preempt.h>
+#include <linux/locallock.h>
 
 DECLARE_PER_CPU(struct aa_buffers, aa_buffers);
+DECLARE_LOCAL_IRQ_LOCK(aa_buffers_lock);
 
 #define COUNT_ARGS(X...) COUNT_ARGS_HELPER(, ##X, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
 #define COUNT_ARGS_HELPER(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, n, X...) n
@@ -54,12 +55,24 @@ DECLARE_PER_CPU(struct aa_buffers, aa_bu
 
 #define for_each_cpu_buffer(I) for ((I) = 0; (I) < MAX_PATH_BUFFERS; (I)++)
 
-#ifdef CONFIG_DEBUG_PREEMPT
+#ifdef CONFIG_PREEMPT_RT_BASE
+
+static inline void AA_BUG_PREEMPT_ENABLED(const char *s)
+{
+	struct local_irq_lock *lv;
+
+	lv = this_cpu_ptr(&aa_buffers_lock);
+	WARN_ONCE(lv->owner != current,
+		  "__get_buffer without aa_buffers_lock\n");
+}
+
+#elif CONFIG_DEBUG_PREEMPT
 #define AA_BUG_PREEMPT_ENABLED(X) AA_BUG(preempt_count() <= 0, X)
 #else
 #define AA_BUG_PREEMPT_ENABLED(X) /* nop */
 #endif
 
+
 #define __get_buffer(N) ({					\
 	struct aa_buffers *__cpu_var; \
 	AA_BUG_PREEMPT_ENABLED("__get_buffer without preempt disabled");  \
@@ -72,14 +85,14 @@ DECLARE_PER_CPU(struct aa_buffers, aa_bu
 
 #define get_buffers(X...)	\
 do {				\
-	preempt_disable();	\
+	local_lock(aa_buffers_lock);	\
 	__get_buffers(X);	\
 } while (0)
 
 #define put_buffers(X, Y...)	\
 do {				\
 	__put_buffers(X, Y);	\
-	preempt_enable();	\
+	local_unlock(aa_buffers_lock);	\
 } while (0)
 
 #endif /* __AA_PATH_H */
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -42,7 +42,7 @@
 int apparmor_initialized __initdata;
 
 DEFINE_PER_CPU(struct aa_buffers, aa_buffers);
-
+DEFINE_LOCAL_IRQ_LOCK(aa_buffers_lock);
 
 /*
  * LSM hook functions