diff mbox series

[SRU,J,2/2] rcu-tasks: Provide rcu_trace_implies_rcu_gp()

Message ID 20240415205939.141814-3-bethany.jamison@canonical.com
State New
Headers show
Series CVE-2023-52447 | expand

Commit Message

Bethany Jamison April 15, 2024, 8:59 p.m. UTC 
From: "Paul E. McKenney" <paulmck@kernel.org>

As an accident of implementation, an RCU Tasks Trace grace period also
acts as an RCU grace period.  However, this could change at any time.
This commit therefore creates an rcu_trace_implies_rcu_gp() that currently
returns true to codify this accident.  Code relying on this accident
must call this function to verify that this accident is still happening.

Reported-by: Hou Tao <houtao@huaweicloud.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Link: https://lore.kernel.org/r/20221014113946.965131-2-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
(cherry picked from commit e6c86c513f440bec5f1046539c7e3c6c653842da)
CVE-2023-52447
Signed-off-by: Bethany Jamison <bethany.jamison@canonical.com>
---
 include/linux/rcupdate.h | 12 ++++++++++++
 kernel/rcu/tasks.h       |  2 ++
 2 files changed, 14 insertions(+)
diff mbox series

Patch

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 13bddb841ceb1..e3b12de36e924 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -205,6 +205,18 @@  static inline void exit_tasks_rcu_stop(void) { }
 static inline void exit_tasks_rcu_finish(void) { }
 #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
 
+/**
+ * rcu_trace_implies_rcu_gp - does an RCU Tasks Trace grace period imply an RCU grace period?
+ *
+ * As an accident of implementation, an RCU Tasks Trace grace period also
+ * acts as an RCU grace period.  However, this could change at any time.
+ * Code relying on this accident must call this function to verify that
+ * this accident is still happening.
+ *
+ * You have been warned!
+ */
+static inline bool rcu_trace_implies_rcu_gp(void) { return true; }
+
 /**
  * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
  *
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 96722dae824b5..3ebb0bbe8ede3 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1098,6 +1098,8 @@  static void rcu_tasks_trace_postscan(struct list_head *hop)
 
 	// Wait for late-stage exiting tasks to finish exiting.
 	// These might have passed the call to exit_tasks_rcu_finish().
+
+	// If you remove the following line, update rcu_trace_implies_rcu_gp()!!!
 	synchronize_rcu();
 	// Any tasks that exit after this point will set ->trc_reader_checked.
 }