Subject: [PATCH bpf-next] bpf: check that BPF programs run with preemption disabled

From: Alexei Starovoitov <[email-masked]>
Date: Mon, 28 Jan 2019 17:21:52 -0800

From: Peter Zijlstra <[email-masked]>

Introduce cant_sleep() macro for annotation of functions that cannot sleep.

Use it in BPF_PROG_RUN to catch execution of BPF programs
in preemptable context.

Suggested-by: Jann Horn <[email-masked]>
Signed-off-by: Peter Zijlstra (Intel) <[email-masked]>
Signed-off-by: Alexei Starovoitov <[email-masked]>
---
 include/linux/filter.h |  2 +-
 include/linux/kernel.h | 14 ++++++++++++--
 kernel/sched/core.c    | 28 ++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index e4b473f85b46..7e87863617b3 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -533,7 +533,7 @@ struct sk_filter {
 	struct bpf_prog	*prog;
 };
 
-#define BPF_PROG_RUN(filter, ctx)  (*(filter)->bpf_func)(ctx, (filter)->insnsi)
+#define BPF_PROG_RUN(filter, ctx)  ({ cant_sleep(); (*(filter)->bpf_func)(ctx, (filter)->insnsi); })
 
 #define BPF_SKB_CB_LEN QDISC_CB_PRIV_LEN
 
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 8f0e68e250a7..a8868a32098c 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -245,8 +245,10 @@ extern int _cond_resched(void);
 #endif
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
-  void ___might_sleep(const char *file, int line, int preempt_offset);
-  void __might_sleep(const char *file, int line, int preempt_offset);
+extern void ___might_sleep(const char *file, int line, int preempt_offset);
+extern void __might_sleep(const char *file, int line, int preempt_offset);
+extern void __cant_sleep(const char *file, int line, int preempt_offset);
+
 /**
  * might_sleep - annotation for functions that can sleep
  *
@@ -259,6 +261,13 @@ extern int _cond_resched(void);
  */
 # define might_sleep() \
 	do { __might_sleep(__FILE__, __LINE__, 0); might_resched(); } while (0)
+/**
+ * cant_sleep - annotation for functions that cannot sleep
+ *
+ * this macro will print a stack trace if it is executed with preemption enabled
+ */
+# define cant_sleep() \
+	do { __cant_sleep(__FILE__, __LINE__, 0); } while (0)
 # define sched_annotate_sleep()	(current->task_state_change = 0)
 #else
   static inline void ___might_sleep(const char *file, int line,
@@ -266,6 +275,7 @@ extern int _cond_resched(void);
   static inline void __might_sleep(const char *file, int line,
 				   int preempt_offset) { }
 # define might_sleep() do { might_resched(); } while (0)
+# define cant_sleep() do { } while (0)
 # define sched_annotate_sleep() do { } while (0)
 #endif
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a674c7db2f29..1dcbff62f973 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6149,6 +6149,34 @@ void ___might_sleep(const char *file, int line, int preempt_offset)
 	add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
 }
 EXPORT_SYMBOL(___might_sleep);
+
+void __cant_sleep(const char *file, int line, int preempt_offset)
+{
+	static unsigned long prev_jiffy;
+
+	if (irqs_disabled())
+		return;
+
+	if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
+		return;
+
+	if (preempt_count() > preempt_offset)
+		return;
+
+	if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
+		return;
+	prev_jiffy = jiffies;
+
+	printk(KERN_ERR "BUG: assuming atomic context at %s:%d\n", file, line);
+	printk(KERN_ERR "in_atomic(): %d, irqs_disabled(): %d, pid: %d, name: %s\n",
+			in_atomic(), irqs_disabled(),
+			current->pid, current->comm);
+
+	debug_show_held_locks(current);
+	dump_stack();
+	add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
+}
+EXPORT_SYMBOL_GPL(__cant_sleep);
 #endif
 
 #ifdef CONFIG_MAGIC_SYSRQ
-- 
2.20.0