[RFC PATCH 02/16] rv: Add runtime reactors interface

[Daniel Bristot de Oliveira]

A runtime monitor can cause a reaction to the detection of an
exception on the model's execution. By default, the monitors have
tracing reactions, printing the monitor output via tracepoints.
But other reactions can be added (on-demand) via this interface.

The user interface resembles the kernel tracing interface and
presents these files:

"available_reactors"
  - Reading shows the available reactors, one per line.

   For example:
   [root@f32 rv]# cat available_reactors
   nop
   panic
   printk

 "reacting_on"
   - It is an on/off general switch for reactors, disabling
   all reactions.

 "monitors/MONITOR/reactors"
   - List available reactors, with the select reaction for the given
   MONITOR inside []. The default one is the nop (no operation)
   reactor.
   - Writing the name of a reactor enables it to the given
   MONITOR.

   For example:
   [root@f32 rv]# cat monitors/wip/reactors
   [nop]
   panic
   printk
   [root@f32 rv]# echo panic > monitors/wip/reactors
   [root@f32 rv]# cat monitors/wip/reactors
   nop
   [panic]
   printk

Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Gabriele Paoloni <gabriele.paoloni@xxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Clark Williams <williams@xxxxxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
---
 include/linux/rv.h            |  10 +
 kernel/trace/rv/Kconfig       |  14 +
 kernel/trace/rv/Makefile      |   1 +
 kernel/trace/rv/rv.c          |  17 +-
 kernel/trace/rv/rv.h          |  19 ++
 kernel/trace/rv/rv_reactors.c | 478 ++++++++++++++++++++++++++++++++++
 6 files changed, 537 insertions(+), 2 deletions(-)
 create mode 100644 kernel/trace/rv/rv_reactors.c

diff --git a/include/linux/rv.h b/include/linux/rv.h
index 04f94919ebb0..1568b48f07a7 100644
--- a/include/linux/rv.h
+++ b/include/linux/rv.h
@@ -6,6 +6,11 @@
  *
  * Copyright (C) 2019-2021 Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
  */
+struct rv_reactor {
+	char			*name;
+	char			*description;
+	void			(*react)(char *);
+};
 
 struct rv_monitor {
 	const char		*name;
@@ -14,8 +19,13 @@ struct rv_monitor {
 	int			(*start)(void);
 	void			(*stop)(void);
 	void			(*reset)(void);
+	void			(*react)(char *);
 };
 
 extern bool monitoring_on;
 int rv_unregister_monitor(struct rv_monitor *monitor);
 int rv_register_monitor(struct rv_monitor *monitor);
+
+extern bool reacting_on;
+int rv_unregister_reactor(struct rv_reactor *reactor);
+int rv_register_reactor(struct rv_reactor *reactor);
diff --git a/kernel/trace/rv/Kconfig b/kernel/trace/rv/Kconfig
index e8e65cfc7959..74eb2f216255 100644
--- a/kernel/trace/rv/Kconfig
+++ b/kernel/trace/rv/Kconfig
@@ -11,3 +11,17 @@ menuconfig RV
 	  theorem proving). RV works by analyzing the trace of the system's
 	  actual execution, comparing it against a formal specification of
 	  the system behavior.
+
+if RV
+
+config RV_REACTORS
+	bool "Runtime verification reactors"
+	default y if RV
+	help
+	  Enables the online runtime verification reactors. A runtime
+	  monitor can cause a reaction to the detection of an exception
+	  on the model's execution. By default, the monitors have
+	  tracing reactions, printing the monitor output via tracepoints,
+	  but other reactions can be added (on-demand) via this interface.
+
+endif # RV
diff --git a/kernel/trace/rv/Makefile b/kernel/trace/rv/Makefile
index fd995379df67..8944274d9b41 100644
--- a/kernel/trace/rv/Makefile
+++ b/kernel/trace/rv/Makefile
@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0
 
 obj-$(CONFIG_RV) += rv.o
+obj-$(CONFIG_RV_REACTORS) += rv_reactors.o
diff --git a/kernel/trace/rv/rv.c b/kernel/trace/rv/rv.c
index e6e1acfc8666..9c7ea300fab6 100644
--- a/kernel/trace/rv/rv.c
+++ b/kernel/trace/rv/rv.c
@@ -312,8 +312,13 @@ static int create_monitor_dir(struct rv_monitor_def *mdef)
 		retval = -ENOMEM;
 		goto out_remove_root;
 	}
+#ifdef CONFIG_RV_REACTORS
+	retval = reactor_create_monitor_files(mdef);
+	if (retval)
+		goto out_remove_root;
+#endif
 
-	return retval;
+	return 0;
 
 out_remove_root:
 	rv_remove(mdef->root_d);
@@ -621,7 +626,11 @@ int rv_register_monitor(struct rv_monitor *monitor)
 
 	r->monitor = monitor;
 
-	create_monitor_dir(r);
+	retval = create_monitor_dir(r);
+	if (retval) {
+		kfree(r);
+		goto out_unlock;
+	}
 
 	list_add_tail(&r->list, &rv_monitors_list);
 
@@ -681,6 +690,10 @@ int __init rv_init_interface(void)
 	rv_create_file("monitoring_on", 0600, rv_root.root_dir, NULL,
 		       &monitoring_on_fops);
 
+#ifdef CONFIG_RV_REACTORS
+	init_rv_reactors(rv_root.root_dir);
+	reacting_on=true;
+#endif
 	monitoring_on=true;
 
 	return 0;
diff --git a/kernel/trace/rv/rv.h b/kernel/trace/rv/rv.h
index 30056469e514..82f64c2b6a50 100644
--- a/kernel/trace/rv/rv.h
+++ b/kernel/trace/rv/rv.h
@@ -14,12 +14,25 @@ struct rv_interface {
 #define rv_remove		tracefs_remove
 
 #define MAX_RV_MONITOR_NAME_SIZE	100
+#define MAX_RV_REACTOR_NAME_SIZE	100
 
 extern struct mutex interface_lock;
 
+#ifdef CONFIG_RV_REACTORS
+struct rv_reactor_def {
+	struct list_head list;
+	struct rv_reactor *reactor;
+	/* protected by the monitor interface lock */
+	int counter;
+};
+#endif
+
 struct rv_monitor_def {
 	struct list_head list;
 	struct rv_monitor *monitor;
+#ifdef CONFIG_RV_REACTORS
+	struct rv_reactor_def *rdef;
+#endif
 	struct dentry *root_d;
 	bool enabled;
 	bool reacting;
@@ -29,3 +42,9 @@ extern bool monitoring_on;
 struct dentry *get_monitors_root(void);
 void reset_all_monitors(void);
 int init_rv_monitors(struct dentry *root_dir);
+
+#ifdef CONFIG_RV_REACTORS
+extern bool reacting_on;
+int reactor_create_monitor_files(struct rv_monitor_def *mdef);
+int init_rv_reactors(struct dentry *root_dir);
+#endif
diff --git a/kernel/trace/rv/rv_reactors.c b/kernel/trace/rv/rv_reactors.c
new file mode 100644
index 000000000000..042a264851e6
--- /dev/null
+++ b/kernel/trace/rv/rv_reactors.c
@@ -0,0 +1,478 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Runtime reactor interface.
+ *
+ * A runtime monitor can cause a reaction to the detection of an
+ * exception on the model's execution. By default, the monitors have
+ * tracing reactions, printing the monitor output via tracepoints.
+ * But other reactions can be added (on-demand) via this interface.
+ *
+ * == Registering reactors ==
+ *
+ * The struct rv_reactor defines a callback function to be executed
+ * in case of a model exception happens. The callback function
+ * receives a message to be (optionally) printed before executing
+ * the reaction.
+ *
+ * A RV reactor is registered via:
+ *   int rv_register_reactor(struct rv_reactor *reactor)
+ * And unregistered via:
+ *   int rv_unregister_reactor(struct rv_reactor *reactor)
+ *
+ * These functions are exported to modules, enabling reactors to be
+ * dynamically loaded.
+ *
+ * == User interface ==
+ *
+ * The user interface resembles the kernel tracing interface and
+ * presents these files:
+ *
+ *  "available_reactors"
+ *    - List the available reactors, one per line.
+ *
+ *    For example:
+ *    [root@f32 rv]# cat available_reactors
+ *    nop
+ *    panic
+ *    printk
+ *
+ *  "reacting_on"
+ *    - It is an on/off general switch for reactors, disabling
+ *    all reactions.
+ *
+ *  "monitors/MONITOR/reactors"
+ *    - List available reactors, with the select reaction for the given
+ *    MONITOR inside []. The defaul one is the nop (no operation)
+ *    reactor.
+ *    - Writing the name of an reactor enables it to the given
+ *    MONITOR.
+ *
+ *    For example:
+ *    [root@f32 rv]# cat monitors/wip/reactors
+ *    [nop]
+ *    panic
+ *    printk
+ *    [root@f32 rv]# echo panic > monitors/wip/reactors
+ *    [root@f32 rv]# cat monitors/wip/reactors
+ *    nop
+ *    [panic]
+ *    printk
+ *
+ * Copyright (C) 2019-2021 Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
+ */
+
+#include <linux/slab.h>
+
+#include "rv.h"
+
+bool __read_mostly reacting_on = false;
+EXPORT_SYMBOL_GPL(reacting_on);
+
+/*
+ * Interface for the reactor register.
+ */
+LIST_HEAD(rv_reactors_list);
+
+struct rv_reactor_def *get_reactor_rdef_by_name(char *name)
+{
+	struct rv_reactor_def *r;
+	list_for_each_entry(r, &rv_reactors_list, list) {
+		if (strcmp(name, r->reactor->name) == 0)
+			return r;
+	}
+
+	return NULL;
+}
+
+/*
+ * Available reactors seq functions.
+ */
+static int reactors_show(struct seq_file *m, void *p)
+{
+	struct rv_reactor_def *rea_def = p;
+	seq_printf(m, "%s\n", rea_def->reactor->name);
+	return 0;
+}
+
+static void reactors_stop(struct seq_file *m, void *p)
+{
+	mutex_unlock(&interface_lock);
+}
+
+static void *reactors_start(struct seq_file *m, loff_t *pos)
+{
+	mutex_lock(&interface_lock);
+	return seq_list_start(&rv_reactors_list, *pos);
+}
+
+static void *reactors_next(struct seq_file *m, void *p, loff_t *pos)
+{
+	return seq_list_next(p, &rv_reactors_list, pos);
+}
+
+
+/*
+ * available reactors seq definition.
+ */
+static const struct seq_operations available_reactors_seq_ops = {
+	.start	= reactors_start,
+	.next	= reactors_next,
+	.stop	= reactors_stop,
+	.show	= reactors_show
+};
+
+/*
+ * available_reactors interface.
+ */
+static int available_reactors_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &available_reactors_seq_ops);
+};
+
+static struct file_operations available_reactors_ops = {
+	.open    = available_reactors_open,
+	.read    = seq_read,
+	.llseek  = seq_lseek,
+	.release = seq_release
+};
+
+/*
+ * Monitor reactor file.
+ */
+static int monitor_reactor_show(struct seq_file *m, void *p)
+{
+	struct rv_monitor_def *mdef = m->private;
+	struct rv_reactor_def *rdef = p;
+
+	if (mdef->rdef == rdef)
+		seq_printf(m, "[%s]\n", rdef->reactor->name);
+	else
+		seq_printf(m, "%s\n", rdef->reactor->name);
+	return 0;
+}
+
+/*
+ * available reactors seq definition.
+ */
+static const struct seq_operations monitor_reactors_seq_ops = {
+	.start	= reactors_start,
+	.next	= reactors_next,
+	.stop	= reactors_stop,
+	.show	= monitor_reactor_show
+};
+
+static ssize_t
+monitor_reactors_write(struct file *file, const char __user *user_buf,
+		      size_t count, loff_t *ppos)
+{
+	char buff[MAX_RV_REACTOR_NAME_SIZE+1];
+	struct rv_monitor_def *mdef;
+	struct rv_reactor_def *rdef;
+	struct seq_file *seq_f;
+	int retval = -EINVAL;
+	char *ptr = buff;
+	int len;
+
+	if (count < 1 || count > MAX_RV_REACTOR_NAME_SIZE+1)
+		return -EINVAL;
+
+	memset(buff, 0, sizeof(buff));
+
+	retval = simple_write_to_buffer(buff, sizeof(buff)-1, ppos, user_buf,
+					count);
+	if (!retval)
+		return -EFAULT;
+
+	len = strlen(ptr);
+	if (!len)
+		return count;
+	/*
+	 * remove the \n
+	 */
+	ptr[len-1]='\0';
+
+	/*
+	 * See monitor_reactors_open()
+	 */
+	seq_f = file->private_data;
+	mdef = seq_f->private;
+
+	mutex_lock(&interface_lock);
+
+	retval = -EINVAL;
+
+	/*
+	 * nop special case: disable reacting.
+	 */
+	if (strcmp(ptr, "nop") == 0) {
+
+		if (mdef->monitor->enabled)
+			mdef->monitor->stop();
+
+		mdef->rdef = get_reactor_rdef_by_name("nop");
+		mdef->reacting = false;
+		mdef->monitor->react = NULL;
+
+		if (mdef->monitor->enabled)
+			mdef->monitor->start();
+
+		retval = count;
+		goto unlock;
+	}
+
+	list_for_each_entry(rdef, &rv_reactors_list, list) {
+		if (strcmp(ptr, rdef->reactor->name) == 0) {
+			/*
+			 * found!
+			 */
+			if (mdef->monitor->enabled)
+				mdef->monitor->stop();
+
+			mdef->rdef = rdef;
+			mdef->reacting = true;
+			mdef->monitor->react = rdef->reactor->react;
+
+			if (mdef->monitor->enabled)
+				mdef->monitor->start();
+
+			retval=count;
+			break;
+		}
+	}
+
+unlock:
+	mutex_unlock(&interface_lock);
+
+	return retval;
+}
+
+/*
+ * available_reactors interface.
+ */
+static int monitor_reactors_open(struct inode *inode, struct file *file)
+{
+	/*
+	 * create file "private" info is stored in the inode->i_private
+	 */
+	struct rv_monitor_def *mdef = inode->i_private;
+	struct seq_file *seq_f;
+	int ret;
+
+
+	ret = seq_open(file, &monitor_reactors_seq_ops);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * seq_open stores the seq_file on the file->private data.
+	 */
+	seq_f = file->private_data;
+	/*
+	 * Copy the create file "private" data to the seq_file
+	 * private data.
+	 */
+	seq_f->private = mdef;
+
+	return 0;
+};
+
+static struct file_operations monitor_reactors_ops = {
+	.open    = monitor_reactors_open,
+	.read    = seq_read,
+	.llseek  = seq_lseek,
+	.release = seq_release,
+	.write = monitor_reactors_write
+};
+
+static int __rv_register_reactor(struct rv_reactor *reactor)
+{
+	struct rv_reactor_def *r;
+
+	list_for_each_entry(r, &rv_reactors_list, list) {
+		if (strcmp(reactor->name, r->reactor->name) == 0) {
+			pr_info("Reactor %s is already registered\n",
+				reactor->name);
+			return -EINVAL;
+		}
+	}
+
+	r = kzalloc(sizeof(struct rv_reactor_def), GFP_KERNEL);
+	if (!r)
+		return -ENOMEM;
+
+	r->reactor = reactor;
+	r->counter = 0;
+
+	list_add_tail(&r->list, &rv_reactors_list);
+
+	return 0;
+}
+
+/**
+ * rv_register_reactor - register a rv reactor.
+ * @reactor:    The rv_reactor to be registered.
+ *
+ * Returns 0 if successful, error otherwise.
+ */
+int rv_register_reactor(struct rv_reactor *reactor)
+{
+	int retval = 0;
+
+	if (strlen(reactor->name) >= MAX_RV_REACTOR_NAME_SIZE) {
+		pr_info("Reactor %s has a name longer than %d\n",
+			reactor->name, MAX_RV_MONITOR_NAME_SIZE);
+		return -EINVAL;
+	}
+
+	mutex_lock(&interface_lock);
+	retval = __rv_register_reactor(reactor);
+	mutex_unlock(&interface_lock);
+	return retval;
+}
+EXPORT_SYMBOL_GPL(rv_register_reactor);
+
+/**
+ * rv_unregister_reactor - unregister a rv reactor.
+ * @reactor:    The rv_reactor to be unregistered.
+ *
+ * Returns 0 if successful, error otherwise.
+ */
+int rv_unregister_reactor(struct rv_reactor *reactor)
+{
+	struct rv_reactor_def *ptr, *next;
+
+	mutex_lock(&interface_lock);
+
+	list_for_each_entry_safe(ptr, next, &rv_reactors_list, list) {
+		if (strcmp(reactor->name, ptr->reactor->name) == 0) {
+
+			if (!ptr->counter) {
+				list_del(&ptr->list);
+			} else {
+				printk("rv: the rv_reactor %s is in use by %d monitor(s)\n",
+					ptr->reactor->name, ptr->counter);
+				printk("rv: the rv_reactor %s cannot be removed\n",
+					ptr->reactor->name);
+				return -EBUSY;
+			}
+
+		}
+	}
+
+	mutex_unlock(&interface_lock);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(rv_unregister_reactor);
+
+/*
+ * reacting_on interface.
+ */
+static ssize_t reacting_on_read_data(struct file *filp,
+				     char __user *user_buf,
+				     size_t count, loff_t *ppos)
+{
+	char buff[4];
+
+	memset(buff, 0, sizeof(buff));
+
+	mutex_lock(&interface_lock);
+	sprintf(buff, "%d\n", reacting_on);
+	mutex_unlock(&interface_lock);
+
+	return simple_read_from_buffer(user_buf, count, ppos,
+				       buff, strlen(buff)+1);
+}
+
+static void turn_reacting_off(void)
+{
+	reacting_on=false;
+}
+
+static void turn_reacting_on(void)
+{
+	reacting_on=true;
+}
+
+static ssize_t
+reacting_on_write_data(struct file *filp, const char __user *user_buf,
+		       size_t count, loff_t *ppos)
+{
+	int retval;
+	u64 val;
+
+	retval = kstrtoull_from_user(user_buf, count, 10, &val);
+	if (retval)
+		return retval;
+
+        retval = count;
+
+	mutex_lock(&interface_lock);
+
+	switch (val) {
+		case 0:
+			turn_reacting_off();
+			break;
+		case 1:
+			turn_reacting_on();
+			break;
+		default:
+			retval = -EINVAL;
+	}
+
+	mutex_unlock(&interface_lock);
+
+	return retval;
+}
+
+static const struct file_operations reacting_on_fops = {
+	.open   = simple_open,
+	.llseek = no_llseek,
+	.write  = reacting_on_write_data,
+	.read   = reacting_on_read_data,
+};
+
+
+int reactor_create_monitor_files(struct rv_monitor_def *mdef)
+{
+	struct dentry *tmp;
+
+	tmp = rv_create_file("reactors", 0400, mdef->root_d, mdef,
+			     &monitor_reactors_ops);
+	if (!tmp)
+		return -ENOMEM;
+
+	/*
+	 * Configure as the rv_nop reactor.
+	 */
+	mdef->rdef = get_reactor_rdef_by_name("nop");
+	mdef->reacting = false;
+	return 0;
+}
+
+/*
+ * None reactor register
+ */
+static void rv_nop_reaction(char *msg)
+{
+	return;
+}
+
+struct rv_reactor rv_nop = {
+	.name = "nop",
+	.description = "no-operation reactor: do nothing.",
+	.react = rv_nop_reaction
+};
+
+/*
+ * This section collects the rv/ root dir files and folders.
+ */
+int init_rv_reactors(struct dentry *root_dir)
+{
+	rv_create_file("available_reactors", 0400, root_dir, NULL,
+		       &available_reactors_ops);
+	rv_create_file("reacting_on", 0600, root_dir, NULL, &reacting_on_fops);
+
+	__rv_register_reactor(&rv_nop);
+
+	return 0;
+}
-- 
2.26.2