From: Miroslav Benes <mbenes@suse.cz>
Date: Wed, 16 Oct 2019 13:33:13 +0200
Subject: ftrace: Introduce PERMANENT ftrace_ops flag
Git-commit: 7162431dcf72032835d369c8d7b51311df407938
Patch-mainline: v5.5-rc1
References: bsc#1120853

Livepatch uses ftrace for redirection to new patched functions. It means
that if ftrace is disabled, all live patched functions are disabled as
well. Toggling global 'ftrace_enabled' sysctl thus affect it directly.
It is not a problem per se, because only administrator can set sysctl
values, but it still may be surprising.

Introduce PERMANENT ftrace_ops flag to amend this. If the
FTRACE_OPS_FL_PERMANENT is set on any ftrace ops, the tracing cannot be
disabled by disabling ftrace_enabled. Equally, a callback with the flag
set cannot be registered if ftrace_enabled is disabled.

Link: http://lkml.kernel.org/r/20191016113316.13415-2-mbenes@suse.cz

Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 Documentation/trace/ftrace.txt |    4 +++-
 include/linux/ftrace.h         |    3 +++
 kernel/livepatch/patch.c       |    3 ++-
 kernel/trace/ftrace.c          |   23 +++++++++++++++++++++--
 4 files changed, 29 insertions(+), 4 deletions(-)

--- a/Documentation/trace/ftrace.txt
+++ b/Documentation/trace/ftrace.txt
@@ -2440,7 +2440,9 @@ Note, the proc sysctl ftrace_enable is a
 function tracer. By default it is enabled (when function tracing is
 enabled in the kernel). If it is disabled, all function tracing is
 disabled. This includes not only the function tracers for ftrace, but
-also for any other uses (perf, kprobes, stack tracing, profiling, etc).
+also for any other uses (perf, kprobes, stack tracing, profiling, etc). It
+cannot be disabled if there is a callback with FTRACE_OPS_FL_PERMANENT set
+registered.
 
 Please disable this with care.
 
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -119,6 +119,8 @@ ftrace_func_t ftrace_ops_get_func(struct
  *            for any of the functions that this ops will be registered for, then
  *            this ops will fail to register or set_filter_ip.
  * PID     - Is affected by set_ftrace_pid (allows filtering on those pids)
+ * PERMANENT - Set when the ops is permanent and should not be affected by
+ *             ftrace_enabled.
  */
 enum {
 	FTRACE_OPS_FL_ENABLED			= 1 << 0,
@@ -137,6 +139,7 @@ enum {
 	FTRACE_OPS_FL_IPMODIFY			= 1 << 13,
 	FTRACE_OPS_FL_PID			= 1 << 14,
 	FTRACE_OPS_FL_RCU			= 1 << 15,
+	FTRACE_OPS_FL_PERMANENT                 = 1 << 16,
 };
 
 #ifdef CONFIG_DYNAMIC_FTRACE
--- a/kernel/livepatch/patch.c
+++ b/kernel/livepatch/patch.c
@@ -208,7 +208,8 @@ static int klp_patch_func(struct klp_fun
 		ops->fops.func = klp_ftrace_handler;
 		ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
 				  FTRACE_OPS_FL_DYNAMIC |
-				  FTRACE_OPS_FL_IPMODIFY;
+				  FTRACE_OPS_FL_IPMODIFY |
+				  FTRACE_OPS_FL_PERMANENT;
 
 		list_add(&ops->node, &klp_ops);
 
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -407,6 +407,8 @@ static int __register_ftrace_function(st
 	if (ops->flags & FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED)
 		ops->flags |= FTRACE_OPS_FL_SAVE_REGS;
 #endif
+	if (!ftrace_enabled && (ops->flags & FTRACE_OPS_FL_PERMANENT))
+		return -EBUSY;
 
 	if (!core_kernel_data((unsigned long)ops))
 		ops->flags |= FTRACE_OPS_FL_DYNAMIC;
@@ -6129,6 +6131,18 @@ int unregister_ftrace_function(struct ft
 }
 EXPORT_SYMBOL_GPL(unregister_ftrace_function);
 
+static bool is_permanent_ops_registered(void)
+{
+	struct ftrace_ops *op;
+
+	do_for_each_ftrace_op(op, ftrace_ops_list) {
+		if (op->flags & FTRACE_OPS_FL_PERMANENT)
+			return true;
+	} while_for_each_ftrace_op(op);
+
+	return false;
+}
+
 int
 ftrace_enable_sysctl(struct ctl_table *table, int write,
 		     void __user *buffer, size_t *lenp,
@@ -6146,8 +6160,6 @@ ftrace_enable_sysctl(struct ctl_table *t
 	if (ret || !write || (last_ftrace_enabled == !!ftrace_enabled))
 		goto out;
 
-	last_ftrace_enabled = !!ftrace_enabled;
-
 	if (ftrace_enabled) {
 
 		/* we are starting ftrace again */
@@ -6157,12 +6169,19 @@ ftrace_enable_sysctl(struct ctl_table *t
 		ftrace_startup_sysctl();
 
 	} else {
+		if (is_permanent_ops_registered()) {
+			ftrace_enabled = true;
+			ret = -EBUSY;
+			goto out;
+		}
+
 		/* stopping ftrace calls (just send to ftrace_stub) */
 		ftrace_trace_function = ftrace_stub;
 
 		ftrace_shutdown_sysctl();
 	}
 
+	last_ftrace_enabled = !!ftrace_enabled;
  out:
 	mutex_unlock(&ftrace_lock);
 	return ret;